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Wood pellets is an example of biomass used for bioenergy production, usually for heating purposes.

Miscanthus × giganteus, a perennial grass can also be used for bioenergy production.

Biomass (for energy) is matter from recently living (but now dead) organisms which is used for bioenergy production. Examples include wood, wood residues, energy crops, agricultural residues, and organic waste from industry and households.^[1] Wood and wood residues is the largest biomass energy source today. Wood can be used as a fuel directly or processed into pellet fuel or other forms of fuels. Other plants can also be used as fuel, for instance corn, switchgrass, miscanthus and bamboo.^[2] The main waste feedstocks are wood waste, agricultural waste, municipal solid waste, and manufacturing waste. Upgrading raw biomass to higher grade fuels can be achieved by different methods, broadly classified as thermal, chemical, or biochemical.

The climate impact of bioenergy varies considerably depending on where biomass feedstocks come from and how they are grown.^[3] For example, burning wood for energy releases carbon dioxide; those emissions can be significantly offset if the trees that were harvested are replaced by new trees in a well-managed forest, as the new trees will absorb carbon dioxide from the air as they grow.^[4] However, the establishment and cultivation of bioenergy crops can displace natural ecosystems, degrade soils, and consume water resources and synthetic fertilisers.^[5]^[6]

In 2020 biomass produced 58 EJ (exajoules) of energy, compared to 172 EJ from crude oil, 157 EJ from coal, 138 EJ from natural gas, 29 EJ from nuclear, 16 EJ from hydro and 15 EJ from wind, solar and geothermal combined.^[7]^[a] Approximately 86% of modern bioenergy is used for heating applications, with 9% used for transport and 5% for electricity.^[b] Most of the global bioenergy is produced from forest resources.^[c]

The IEA's Net Zero by 2050 scenario^[d] calls for traditional bioenergy to be phased out by 2030, with modern bioenergy's share increasing from 6.6% in 2020 to 13.1% in 2030 and 18.7% in 2050.^[8] The IPCC (Intergovernmental Panel on Climate Change) believes that bioenergy has a significant climate change mitigation potential if implemented correctly.^[e] Most of the IPCC's pathways including substantial contributions from bioenergy in 2050 (average at 200 EJ).^[9]

Terminology

Biomass (in the context of energy generation) is matter from recently living (but now dead) organisms which is used for bioenergy production. There are variations in how such biomass for energy is defined, e.g. only from plants,^[10] or from plants and algae,^[11] or from plants and animals.^[12] The vast majority of biomass used for bioenergy does come from plants. Bioenergy is a type of renewable energy with potential to assist with climate change mitigation.^[13]

Some people use the terms biomass and biofuel interchangeably, but it is now more common to consider biofuel to be a liquid or gaseous fuel used for transportation, as defined by government authorities in the US and EU.^[f]^[g] From that perspective, biofuel is a subset of biomass.

The European Union's Joint Research Centre defines solid biofuel as raw or processed organic matter of biological origin used for energy, such as firewood, wood chips, and wood pellets.^[14]^: 20–21

Types and uses

Different types of biomass are used for different purposes:

Primary biomass sources that are appropriate for heat or electricity generation but not for transport include: wood, wood residues, wood pellets, agricultural residues, organic waste.
Biomass that is processed into transport fuels can come from corn, sugar cane, and soy.

Biomass is categorized either as biomass harvested directly for energy (primary biomass), or as residues and waste: (secondary biomass).^[15]^[16]

Biomass harvested directly for energy

The main biomass types harvested directly for energy is wood, some food crops and all perennial energy crops. One third of the global forest area of 4 billion hectares is used for wood production or other commercial purposes,^[17] and forests provide 85% of all biomass used for energy globally.^[c] In the EU, forests provide 60% of all biomass used for energy,^[18] with wood residues and waste being the largest source.^[19]

Woody biomass used for energy often consists of trees and bushes harvested for traditional cooking and heating purposes, particularly in developing countries, with 25 EJ per year used globally for these purposes.^[20] This practice is highly polluting. The World Health Organization (WHO) estimates that cooking-related pollution causes 3.8 million annual deaths.^[21] The United Nations Sustainable Development Goal 7 aims for the traditional use of biomass for cooking to be phased out by 2030.^[22] Short-rotation coppices^[h] and short-rotation forests^[i] are also harvested directly for energy, providing 4 EJ of energy,^[20] and are considered sustainable. The potential for these crops and perennial energy crops to provide at least 25 EJ annually by 2050 is estimated.^[20]^[j]

Food crops harvested for energy include sugar-producing crops (such as sugarcane), starch-producing crops (such as corn), and oil-producing crops (such as rapeseed).^[23] Sugarcane is a perennial crop, while corn and rapeseed are annual crops. Sugar- and starch-producing crops are used to make bioethanol, and oil-producing crops are used to make biodiesel. The United States is the largest producer of bioethanol, while the European Union is the largest producer of biodiesel.^[24] The global production of bioethanol and biodiesel provides 2.2 and 1.5 EJ of energy per year, respectively.^[25] Biofuel made from food crops harvested for energy is also known as "first-generation" or "traditional" biofuel and has relatively low emission savings.

The IPCC estimates that between 0.32 and 1.4 billion hectares of marginal land are suitable for bioenergy worldwide.^[k]

Biomass in the form of residues and waste

Residues and waste are by-products from biological material harvested mainly for non-energy purposes. The most important by-products are wood residues, agricultural residues and municipal/industrial waste:

Wood residues are by-products from forestry operations or from the wood processing industry. Had the residues not been collected and used for bioenergy, they would have decayed (and therefore produced emissions)^[l] on the forest floor or in landfills, or been burnt (and produced emissions) at the side of the road in forests or outside wood processing facilities.^[26]

The by-products from forestry operations are called logging residues or forest residues, and consist of tree tops, branches, stumps, damaged or dying or dead trees, irregular or bent stem sections, thinnings (small trees that are cleared away in order to help the bigger trees grow large), and trees removed to reduce wildfire risk.^[m] The extraction level of logging residues differ from region to region,^[n]^[o] but there is an increasing interest in using this feedstock,^[p] since the sustainable potential is large (15 EJ annually).^[q] 68% of the total forest biomass in the EU consists of wood stems, and 32% consists of stumps, branches and tops.^[27]

The by-products from the wood processing industry are called wood processing residues and consist of cut offs, shavings, sawdust, bark, and black liquor.^[r] Wood processing residues have a total energy content of 5.5 EJ annually.^[28] Wood pellets are mainly made from wood processing residues,^[s] and have a total energy content of 0.7 EJ.^[t] Wood chips are made from a combination of feedstocks,^[29] and have a total energy content of 0.8 EJ.^[u]

The energy content in agricultural residues used for energy is approximately 2 EJ.^[v] However, agricultural residues has a large untapped potential. The energy content in the global production of agricultural residues has been estimated to 78 EJ annually, with the largest share from straw (51 EJ).^[w] Others have estimated between 18 and 82 EJ.^[x] The use of agricultural residues and waste that is both sustainable and economically feasible^[15]^: 9 is expected to increase to between 37 and 66 EJ in 2030.^[y]

Municipal waste produced 1.4 EJ and industrial waste 1.1 EJ.^[30] Wood waste from cities and industry also produced 1.1 EJ.^[28] The sustainable potential for wood waste has been estimated to 2–10 EJ.^[31] IEA recommends a dramatic increase in waste utilization to 45 EJ annually in 2050.^[8]

Biomass conversion

Raw biomass can be upgraded into better and more practical fuel simply by compacting it (e.g. wood pellets), or by different conversions broadly classified as thermal, chemical, and biochemical.^[32] Biomass conversion reduces the transport costs as it is cheaper to transport high density commodities.^[15]^: 53

Thermal conversion

Thermal upgrading produces solid, liquid or gaseous fuels, with heat as the dominant conversion driver. The basic alternatives are torrefaction, pyrolysis, and gasification, these are separated principally by how far the chemical reactions involved are allowed to proceed. The advancement of the chemical reactions is mainly controlled by how much oxygen is available, and the conversion temperature.

Torrefaction is a mild form of pyrolysis where organic materials are heated to 400–600 °F (200–300 °C) in a no–to–low oxygen environment.^[33]^[34] The heating process removes (via gasification) the parts of the biomass that has the lowest energy content, while the parts with the highest energy content remain. That is, approximately 30% of the biomass is converted to gas during the torrefaction process, while 70% remains, usually in the form of compacted pellets or briquettes. This solid product is water resistant, easy to grind, non-corrosive, and it contains approximately 85% of the original biomass energy.^[35] Basically the mass part has shrunk more than the energy part, and the consequence is that the calorific value of torrefied biomass increases significantly, to the extent that it can compete with coals used for electricity generation (steam/thermal coals). The energy density of the most common steam coals today is 22–26 GJ/t.^[36] There are other less common, more experimental or proprietary thermal processes that may offer benefits, such as hydrothermal upgrading (sometimes called "wet" torrefaction.)^[z] The hydrothermal upgrade path can be used for both low and high moisture content biomass, e.g. aqueous slurries.^[37]

Pyrolysis entails heating organic materials to 800–900 °F (400–500 °C) in the near complete absence of oxygen. Biomass pyrolysis produces fuels such as bio-oil, charcoal, methane, and hydrogen. Hydrotreating is used to process bio-oil (produced by fast pyrolysis) with hydrogen under elevated temperatures and pressures in the presence of a catalyst to produce renewable diesel, renewable gasoline, and renewable jet fuel.^[38]

Gasification entails heating organic materials to 1,400–1700 °F (800–900 °C) with injections of controlled amounts of oxygen and/or steam into the vessel to produce a carbon monoxide and hydrogen rich gas called synthesis gas or syngas. Syngas can be used as a fuel for diesel engines, for heating, and for generating electricity in gas turbines. It can also be treated to separate the hydrogen from the gas, and the hydrogen can be burned or used in fuel cells. The syngas can be further processed to produce liquid fuels using the Fischer-Tropsch synthesis process.^[32]^[39]

Chemical conversion

A range of chemical processes may be used to convert biomass into other forms, such as to produce a fuel that is more practical to store, transport and use, or to exploit some property of the process itself. Many of these processes are based in large part on similar coal-based processes, such as the Fischer-Tropsch synthesis.^[40] A chemical conversion process known as transesterification is used for converting vegetable oils, animal fats, and greases into fatty acid methyl esters (FAME), which are used to produce biodiesel.^[32]

Biochemical conversion

Biochemical processes have developed in nature to break down the molecules of which biomass is composed, and many of these can be harnessed. In most cases, microorganisms are used to perform the conversion. The processes are called anaerobic digestion, fermentation, and composting.^[41]

Fermentation converts biomass into bioethanol, and anaerobic digestion converts biomass into renewable natural gas (biogas). Bioethanol is used as a vehicle fuel. Renewable natural gas—also called biogas or biomethane—is produced in anaerobic digesters at sewage treatment plants and at dairy and livestock operations. It also forms in and may be captured from solid waste landfills. Properly treated renewable natural gas has the same uses as fossil fuel natural gas.^[32]

Climate impacts

Currently there is a lively debate going on about the real carbon intensity of a number of bioenergy pathways, especially from forestry. The critics are especially concerned about short-term or medium-term climate effects. Critics have emerged both among researchers^[aa] and environmental activists.^[ab]^[ac] At the same time, bioenergy supporters in influential research organizations like the IPCC, IEA, and EU's Joint Research Centre argue that bioenergy is climate friendly when implemented correctly and at an appropriate scale.

The climate impact of bioenergy varies considerably depending on where biomass feedstocks come from and how they are grown.^[42] For example, burning wood for energy releases carbon dioxide; those emissions can be significantly offset if the trees that were harvested are replaced by new trees in a well-managed forest, as the new trees will absorb carbon dioxide from the air as they grow.^[43] However, the establishment and cultivation of bioenergy crops can displace natural ecosystems, degrade soils, and consume water resources and synthetic fertilisers.^[5]^[6]

Approximately one-third of all wood used for traditional heating and cooking in tropical areas is harvested unsustainably.^[44] Bioenergy feedstocks typically require significant amounts of energy to harvest, dry, and transport; the energy usage for these processes may emit greenhouse gases. In some cases, the impacts of land-use change, cultivation, and processing can result in higher overall carbon emissions for bioenergy compared to using fossil fuels.^[6]^[45]

Use of farmland for growing biomass can result in less land being available for growing food. In the United States, around 10% of motor gasoline has been replaced by corn-based ethanol, which requires a significant proportion of the harvest.^[46]^[47] In Malaysia and Indonesia, clearing forests to produce palm oil for biodiesel has led to serious social and environmental effects, as these forests are critical carbon sinks and habitats for diverse species.^[48]^[49] Since photosynthesis captures only a small fraction of the energy in sunlight, producing a given amount of bioenergy requires a large amount of land compared to other renewable energy sources.^[50]

Carbon accounting principles

Different carbon accounting methodologies have a significant impact on the calculated results and therefore on the scientific arguments. Generally, the purpose of carbon accounting is to determine the carbon intensity of an energy scenario, i.e. whether it is carbon positive, carbon neutral or carbon negative. Carbon positive scenarios are likely to be net emitters of CO₂, carbon negative projects are net absorbers of CO₂, while carbon neutral projects balance emissions and absorption perfectly.^[ad]

A project or scenario can be assessed solely on its own merits, specifically the time it takes to pay back removed carbon (carbon payback time.) However, it is common to include alternative scenarios (also called "reference scenarios" or "counterfactuals") for comparison.^[ae] When there is more than one scenario, carbon parity times between these scenarios can be calculated. The alternative scenarios range from scenarios with only modest changes compared to the existing project, all the way to radically different ones (i.e. forest protection or "no-bioenergy" counterfactuals.) Generally, the difference between scenarios is seen as the actual carbon mitigation potential of the scenarios.^[af] In other words, quoted emission savings are relative savings; savings relative to some alternative scenario the researcher suggest. This gives the researcher a large amount of influence over the calculated results.

Carbon accounting system boundaries

In addition to the choice of alternative scenario, other choices has to be made as well. The so-called "system boundaries" determine which carbon emissions/absorptions that will be included in the actual calculation, and which that will be excluded. System boundaries include temporal, spatial, efficiency-related and economic boundaries:^[ag]

Temporal system boundaries

The temporal boundaries define when to start and end carbon counting. Sometimes "early" events are included in the calculation, for instance carbon absorption going on in the forest before the initial harvest. Sometimes "late" events are included as well, for instance emissions caused by end-of-life activities for the infrastructure involved, e.g. demolition of factories. Since the emission and absorption of carbon related to a project or scenario changes with time, the net carbon emission can either be presented as time-dependent (for instance a curve which moves along a time axis), or as a static value; this shows average emissions calculated over a defined time period.

The time-dependent net emission curve will typically show high emissions at the beginning (if the counting starts when the biomass is harvested.) Alternatively, the starting point can be moved back to the planting event; in this case the curve can potentially move below zero (into carbon negative territory) if there is no carbon debt from land use change to pay back, and in addition more and more carbon is absorbed by the planted trees. The emission curve then spikes upward at harvest. The harvested carbon is then being distributed into other carbon pools, and the curve moves in tandem with the amount of carbon that is moved into these new pools (Y axis), and the time it takes for the carbon to move out of the pools and return to the forest via the atmosphere (X axis). As described above, the carbon payback time is the time it takes for the harvested carbon to be returned to the forest, and the carbon parity time is the time it takes for the carbon stored in two competing scenarios to reach the same level.^[ah]

The static carbon emission value is produced by calculating the average annual net emission for a specific time period. The specific time period can be the expected lifetime of the infrastructure involved (typical for life cycle assessments; LCA's), policy relevant time horizons inspired by the Paris agreement (for instance remaining time until 2030, 2050 or 2100),^[51] time spans based on different global warming potentials (GWP; typically 20 or 100 years),^[ai] or other time spans. In the EU, a time span of 20 years is used when quantifying the net carbon effects of a land use change.^[aj] Generally in legislation, the static number approach is preferred over the dynamic, time-dependent curve approach. The number is expressed as a so-called "emission factor" (net emission per produced energy unit, for instance kg CO₂e per GJ), or even simpler as an average greenhouse gas savings percentage for specific bioenergy pathways.^[ak] The EU's published greenhouse gas savings percentages for specific bioenergy pathways used in the Renewable Energy Directive (RED) and other legal documents are based on life cycle assessments (LCA's).^[al]^[am]

Spatial system boundaries

The spatial boundaries define "geographical" borders for carbon emission/absorption calculations. The two most common spatial boundaries for CO₂ absorption and emission in forests are 1.) along the edges of a particular forest stand and 2.) along the edges of a whole forest landscape, which include many forest stands of increasing age (the forest stands are harvested and replanted, one after the other, over as many years as there are stands.) A third option is the so-called increasing stand level carbon accounting method. The researcher has to decide whether to focus on the individual stand, an increasing number of stands, or the whole forest landscape. The IPCC recommends landscape-level carbon accounting.

Further, the researcher has to decide whether emissions from direct/indirect land use change should be included in the calculation. Most researchers include emissions from direct land use change, for instance the emissions caused by cutting down a forest in order to start some agricultural project there instead. The inclusion of indirect land use change effects is more controversial, as they are difficult to quantify accurately.^[an]^[ao] Other choices involve defining the likely spatial boundaries of forests in the future.

Efficiency-related system boundaries

The efficiency-related boundaries define a range of fuel substitution efficiencies for different biomass-combustion pathways. Different supply chains emit different amounts of carbon per supplied energy unit, and different combustion facilities convert the chemical energy stored in different fuels to heat or electrical energy with different efficiencies. The researcher has to know about this and choose a realistic efficiency range for the different biomass-combustion paths under consideration. The chosen efficiencies are used to calculate so-called "displacement factors" – single numbers that shows how efficient fossil carbon is substituted by biogenic carbon.^[ap] If for instance 10 tonnes of carbon are combusted with an efficiency half that of a modern coal plant, only 5 tonnes of coal would actually be counted as displaced (displacement factor 0.5).

Generally, fuel burned in inefficient (old or small) combustion facilities gets assigned lower displacement factors than fuel burned in efficient (new or large) facilities, since more fuel has to be burned (and therefore more CO₂ released) in order to produce the same amount of energy.^[aq]

The displacement factor varies with the carbon intensity of both the biomass fuel and the displaced fossil fuel. If or when bioenergy can achieve negative emissions (e.g. from afforestation, energy grass plantations and/or bioenergy with carbon capture and storage (BECCS),^[ar] or if fossil fuel energy sources with higher emissions in the supply chain start to come online (e.g. because of fracking, or increased use of shale gas), the displacement factor will start to rise. On the other hand, if or when new baseload energy sources with lower emissions than fossil fuels start to come online, the displacement factor will start to drop. Whether a displacement factor change is included in the calculation or not, depends on whether or not it is expected to take place within the time period covered by the relevant scenario's temporal system boundaries.^[as]

Economic system boundaries

The economic boundaries define which market effects to include in the calculation, if any. Changed market conditions can lead to small or large changes in carbon emissions and absorptions from supply chains and forests,^[at] for instance changes in forest area as a response to changes in demand. Macroeconomic events/policy changes can have impacts on forest carbon stock.^[au] Like with indirect land use changes, economic changes can be difficult to quantify however, so some researchers prefer to leave them out of the calculation.^[av]

System boundary impacts

The chosen system boundaries are very important for the calculated results.^[aw] Shorter payback/parity times are calculated when fossil carbon intensity, forest growth rate and biomass conversion efficiency increases, or when the initial forest carbon stock and/or harvest level decreases.^[52] Shorter payback/parity times are also calculated when the researcher choose landscape level over stand level carbon accounting (if carbon accounting starts at the harvest rather than at the planting event.) Conversely, longer payback/parity times are calculated when carbon intensity, growth rate and conversion efficiency decreases, or when the initial carbon stock and/or harvest level increases, or the researcher choose stand level over landscape level carbon accounting.^[ax]

Critics argue that unrealistic system boundary choices are made,^[ay] or that narrow system boundaries lead to misleading conclusions.^[az] Others argue that the wide range of results shows that there is too much leeway available and that the calculations therefore are useless for policy development.^[ba] EU's Join Research Center agrees that different methodologies produce different results,^[bb] but also argue that this is to be expected, since different researchers consciously or unconsciously choose different alternative scenarios/methodologies as a result of their ethical ideals regarding man's optimal relationship with nature. The ethical core of the sustainability debate should be made explicit by researchers, rather than hidden away.^[bc]

Climate impacts expressed as varying with time

The use of boreal stemwood harvested exclusively for bioenergy have a positive climate impact only in the long term, while the use of wood residues have a positive climate impact also in the short to medium term.^[bd]

Short carbon payback/parity times are produced when the most realistic no-bioenergy scenario is a traditional forestry scenario where "good" wood stems are harvested for lumber production, and residues are burned or left behind in the forest or in landfills. The collection of such residues provides material which "[...] would have released its carbon (via decay or burning) back to the atmosphere anyway (over time spans defined by the biome's decay rate) [...]."^[53] In other words, payback and parity times depend on the decay speed. The decay speed depends on a.) location (because decay speed is "[...] roughly proportional to temperature and rainfall [...]"^[54]), and b.) the thickness of the residues.^[be] Residues decay faster in warm and wet areas, and thin residues decay faster than thick residues. Thin residues in warm and wet temperate forests therefore have the fastest decay, while thick residues in cold and dry boreal forests have the slowest decay. If the residues instead are burned in the no-bioenergy scenario, e.g. outside the factories or at roadside in the forests, emissions are instant. In this case, parity times approach zero.^[bf]

Like other scientists, the JRC staff note the high variability in carbon accounting results, and attribute this to different methodologies.^[bg] In the studies examined, the JRC found carbon parity times of 0 to 400 years for stemwood harvested exclusively for bioenergy, depending on different characteristics and assumptions for both the forest/bioenergy system and the alternative fossil system, with the emission intensity of the displaced fossil fuels seen as the most important factor, followed by conversion efficiency and biomass growth rate/rotation time. Other factors relevant for the carbon parity time are the initial carbon stock and the existing harvest level; both higher initial carbon stock and higher harvest level means longer parity times.^[55] Liquid biofuels have high parity times because about half of the energy content of the biomass is lost in the processing.^[bh]

Climate impacts expressed as static numbers

EU's Joint Research Centre has examined a number of bioenergy emission estimates found in literature, and calculated greenhouse gas savings percentages for bioenergy pathways in heat production, transportation fuel production and electricity production, based on those studies. The calculations are based on the attributional LCA accounting principle. It includes all supply chain emissions, from raw material extraction, through energy and material production and manufacturing, to end-of-life treatment and final disposal. It also includes emissions related to the production of the fossil fuels used in the supply chain. It excludes emission/absorption effects that takes place outside its system boundaries, for instance market related, biogeophysical (e.g. albedo), and time-dependent effects. The authors conclude that "[m]ost bio-based commodities release less GHG than fossil products along their supply chain; but the magnitude of GHG emissions vary greatly with logistics, type of feedstocks, land and ecosystem management, resource efficiency, and technology."^[56]

Because of the varied climate mitigation potential for different biofuel pathways, governments and organizations set up different certification schemes to ensure that biomass use is sustainable, for instance the RED (Renewable Energy Directive) in the EU and the ISO standard 13065 by the International Organization for Standardization.^[57] In the US, the RFS (Renewables Fuel Standard) limit the use of traditional biofuels and defines the minimum life-cycle GHG emissions that are acceptable. Biofuels are considered traditional if they achieve up to 20% GHG emission reduction compared to the petrochemical equivalent, advanced if they save at least 50%, and cellulosic if the save more than 60%.^[bj]

The EU's Renewable Energy Directive (RED) states that the typical greenhouse gas emissions savings when replacing fossil fuels with wood pellets from forest residues for heat production varies between 69% and 77%, depending on transport distance: When the distance is between 0 and 2500 km, emission savings is 77%. Emission savings drop to 75% when the distance is between 2500 and 10 000 km, and to 69% when the distance is above 10 000 km. When stemwood is used, emission savings varies between 70% and 77%, depending on transport distance. When wood industry residues are used, savings varies between 79% and 87%.^[bk]

Since the long payback and parity times calculated for some forestry projects is seen as a non-issue for energy crops (except in the cases mentioned above), researchers instead calculate static climate mitigation potentials for these crops, using LCA-based carbon accounting methods. A particular energy crop-based bioenergy project is considered carbon positive, carbon neutral or carbon negative based on the total amount of CO₂ equivalent emissions and absorptions accumulated throughout its entire lifetime: If emissions during agriculture, processing, transport and combustion are higher than what is absorbed (and stored) by the plants, both above and below ground, during the project's lifetime, the project is carbon positive. Likewise, if total absorption is higher than total emissions, the project is carbon negative. In other words, carbon negativity is possible when net carbon accumulation more than compensates for net lifecycle greenhouse gas emissions.

Typically, perennial crops sequester more carbon than annual crops because the root buildup is allowed to continue undisturbed over many years. Also, perennial crops avoid the yearly tillage procedures (plowing, digging) associated with growing annual crops. Tilling helps the soil microbe populations to decompose the available carbon, producing CO₂.^[bl]^[bm]

There is now (2018) consensus in the scientific community that "[...] the GHG [greenhouse gas] balance of perennial bioenergy crop cultivation will often be favourable [...]", also when considering the implicit direct and indirect land use changes.^[bn]

Albedo and evapotranspiration

Forests generally have a low albedo because the majority of the ultraviolet and visible spectrum is absorbed through photosynthesis. For this reason, the greater heat absorption by trees could offset some of the carbon benefits of afforestation (or offset the negative climate impacts of deforestation). In other words: The climate change mitigation effect of carbon sequestration by forests is partially counterbalanced in that reforestation can decrease the reflection of sunlight (albedo).^[58]

Comparisons of GHG emissions at the point of combustion

GHG emissions per produced energy unit at the point of combustion depend on moisture content in the fuel, chemical differences between fuels and conversion efficiencies. Many biomass-only combustion facilities are relatively small and inefficient, compared to the typically much larger coal plants. Further, raw biomass (for instance wood chips) can have higher moisture content than coal (especially if the coal has been dried). When this is the case, more of the wood's inherent energy must be spent solely on evaporating moisture, compared to the drier coal, which means that the amount of CO₂ emitted per unit produced heat will be higher. This moisture problem can be mitigated by modern combustion facilities.^[bo]

Forest biomass on average produces 10-16% more CO₂ than coal and the IPCC estimates 16%.^[59]^[bp] However, focusing on gross emissions misses the point, what counts is the net climate effect from emissions and absorption, taken together.^[bq]^[br] IEA Bioenergy concludes that the additional CO₂ from biomass "[...] is irrelevant if the biomass is derived from sustainably managed forests."^[59]

Sustainable forestry and forest protection

IPCC states that there is disagreement about whether the global forest is shrinking or not, and quote research indicating that tree cover has increased 7.1% between 1982 and 2016.^[bs] The IPCC writes: "While above-ground biomass carbon stocks are estimated to be declining in the tropics, they are increasing globally due to increasing stocks in temperate and boreal forests [...]."^[61]

Old trees have a very high carbon absorption rate, and felling old trees means that this large potential for future carbon absorption is lost.^[62] There is also a loss of soil carbon due to the harvest operations.^[62]

Old trees absorb more CO₂ than young trees, because of the larger leaf area in full grown trees.^[63] However, the old forest (as a whole) will eventually stop absorbing CO₂ because CO₂ emissions from dead trees cancel out the remaining living trees' CO₂ absorption.^[bt] The old forest (or forest stands) are also vulnerable for natural disturbances that produces CO₂. The IPCC found that "[...] landscapes with older forests have accumulated more carbon but their sink strength is diminishing, while landscapes with younger forests contain less carbon but they are removing CO₂ from the atmosphere at a much higher rate [...]."^[64]

The IPCC states that the net climate effect from conversion of unmanaged to managed forest can be positive or negative, depending on circumstances. The carbon stock is reduced, but since managed forests grow faster than unmanaged forests, more carbon is absorbed. Positive climate effects are produced if the harvested biomass is used efficiently.^[bu] There is a tradeoff between the benefits of having a maximized forest carbon stock, not absorbing any more carbon, and the benefits of having a portion of that carbon stock "unlocked", and instead working as a renewable fossil fuel replacement tool, for instance in sectors which are difficult or expensive to decarbonize.^[bv]^[bw]

IEA Bioenergy writes: "forests managed for producing sawn timber, bioenergy and other wood products can make a greater contribution to climate change mitigation than forests managed for conservation alone." Three reasons are given:^[65]

reducing ability to act as a carbon sink when the forest matures.
Wood products can replace other materials that emitted more GHGs during production.
"Carbon in forests is vulnerable to loss through natural events such as insect infestations or wildfires"

Data from FAO show that most wood pellets are produced in regions dominated by sustainably managed forests, such as Europe and North America. Europe (including Russia) produced 54% of the world's wood pellets in 2019, and the forest carbon stock in this area increased from 158.7 to 172.4 Gt between 1990 and 2020. In the EU, above-ground forest biomass increases with 1.3% per year on average, however the increase is slowing down because the forests are maturing.^[66]

Short-term vs long-term climate benefits

Some research groups state that even if the European and North American forest carbon stock is increasing, it simply takes too long for harvested trees to grow back. Bioenergy from sources with high payback and parity times take a long time to have an impact on climate change mitigation. They therefore suggest that the EU should adjust its sustainability criteria so that only renewable energy with carbon payback times of less than 10 years is defined as sustainable,^[bx] for instance wind, solar, biomass from wood residues and tree thinnings that would otherwise be burnt or decompose relatively fast, and biomass from short rotation coppicing (SRC).^[68]

The IPCC states: "While individual stands in a forest may be either sources or sinks, the forest carbon balance is determined by the sum of the net balance of all stands."^[69] IPCC also state that the only universally applicable approach to carbon accounting is the one that accounts for both carbon emissions and carbon removals (absorption) for managed lands (e.g. forest landscapes.)^[by] When the total is calculated, natural disturbances like fires and insect infestations are subtracted, and what remains is the human influence.^[bz]

Forest carbon emission avoidance strategies give a short-term mitigation benefit, but the long-term benefits from sustainable forestry activities are more important:

Relative to a baseline, the largest short-term gains are always achieved through mitigation activities aimed at emission avoidance [...]. But once an emission has been avoided, carbon stocks on that forest will merely be maintained or increased slightly. [...] In the long term, sustainable forest management strategy aimed at maintaining or increasing forest carbon stocks, while producing an annual yield of timber, fibre, or energy from the forest, will generate the largest sustained mitigation benefit.^[69]

Similarly, addressing the issue of climate consequences for modern bioenergy in general, the IPCC states: "Life-cycle GHG emissions of modern bioenergy alternatives are usually lower than those for fossil fuels [...]."^[70] Consequently, most of IPCC's GHG mitigation pathways include substantial deployment of bioenergy technologies.^[9] Limited or no bioenergy pathways leads to increased climate change or shifting bioenergy's mitigation load to other sectors.^[e] In addition, mitigation cost increases.^[ca]

IEA Bioenergy state that an exclusive focus on the short-term make it harder to achieve efficient carbon mitigation in the long term, and compare investments in new bioenergy technologies with investments in other renewable energy technologies that only provide emission reductions after 2030, for instance the scaling-up of battery manufacturing or the development of rail infrastructure.^[cb]

Environmental impacts

The environmental impacts of biomass production need to be taken into account. For instance in 2022, IEA stated that "bioenergy is an important pillar of decarbonisation in the energy transition as a near zero-emission fuel", and that "more efforts are needed to accelerate modern bioenergy deployment to get on track with the Net Zero Scenario [....] while simultaneously ensuring that bioenergy production does not incur negative social and environmental consequences."^[71]

Surface power production densities

The environmental impact caused by biomass or other renewable energy production depends for example on its land use requirements. This parameter is expressed as "surface power production densities" (e.g. power production per square metre). The average lifecycle surface power densities for modern biofuels, wind, hydro and solar power production are 0.3 W/m², 1 W/m², 3 W/m² and 5 W/m², respectively (power in the form of heat for biofuels, and electricity for wind, hydro and solar).^[72] Lifecycle surface power density includes land used by all supporting infrastructure, manufacturing, mining/harvesting and decommissioning. Another estimate is 0.08 W/m² for biofuel, 0.14 W/m² for hydro, 1.84 W/m² for wind, and 6.63 W/m² for solar (median values, with none of the renewable sources exceeding 10 W/m²). Fossil gas has the highest surface density at 482 W/m² while nuclear power at 240 W/m² is the only high-density and low-carbon energy source.^[73]

The reason for the low power density for some of the biofuels is a combination of low yields and only partial utilization of the plant (for instance, ethanol is typically made from sugarcane's sugar content or corn's starch content, while biodiesel is often made from the oil content in rapeseed or soybean).

Biodiversity

Biomass production for bioenergy can have negative impacts on biodiversity.^[75] Oil palm and sugar cane are examples of crops that have been linked to reduced biodiversity.^[76]

Win-win scenarios (good for climate, good for biodiversity) include:^[cd]

Increased use of whole trees from coppice forests, increased use of thin forest residues from boreal forests with slow decay rates, and increased use of all kinds of residues from temperate forests with faster decay rates;
Multi-functional bioenergy landscapes, instead of expansion of monoculture plantations; ^[77]
Afforestation of former agricultural land with mixed or naturally regenerating forests.

Win-lose scenarios (good for the climate, bad for biodiversity) include afforestation on ancient, biodiversity-rich grassland ecosystems which were never forests, and afforestation of former agricultural land with monoculture plantations.^[ce]

Lose-win scenarios (bad for the climate, good for biodiversity) include natural forest expansion on former agricultural land.^[cf]

Lose-lose scenarios include increased use of thick forest residues like stumps from some boreal forests with slow decay rates, and conversion of natural forests into forest plantations.^[cg]

Pollution

Other problems are pollution of soil and water from fertiliser/pesticide use,^[78] and emission of ambient air pollutants, mainly from open field burning of residues.^[79]

The traditional use of wood in cook stoves and open fires produces pollutants, which can lead to severe health and environmental consequences. However, a shift to modern bioenergy contribute to improved livelihoods and can reduce land degradation and impacts on ecosystem services.^[ch] According to the IPCC, there is strong evidence that modern bioenergy have "large positive impacts" on air quality.^[80] Traditional bioenergy is inefficient and the phasing out of this energy source has both large health benefits and large economic benefits.^[ci] When combusted in industrial facilities, most of the pollutants originating from woody biomass reduce by 97-99%, compared to open burning.^[81]

References

Quotes and comments

^ In 2020, the world produced a total of 24.6 EJ of electrical energy from all renewables except bioenergy. The individual contributions consists of 15.5 EJ from hydro, 5.8 EJ from wind, 3 EJ from solar and 0.3 EJ from geothermal (all values converted from TWh with IEA's unit converter.)
^ In 2020, 9.5 EJ of heat energy for industrial applications was consumed, and 5 EJ of heat for buildings. 3.7 EJ of liquid fuels for transportation was produced (ethanol 2.2 EJ, biodiesel 1.5 EJ), and 2.2 EJ in the form of electricity.
^ ^a ^b "The forestry sector is the largest contributor to the bioenergy mix globally. Forestry products including charcoal, fuelwood, pellets and wood chips account for more than 85% of all the biomass used for energy purposes. One of the primary products from forests that are used for bioenergy production is woodfuel. Most of the woodfuel is used for traditional cooking and heating in developing countries in Asia and Africa. Globally, 1.9 billion m³ of woodfuel was used for energy purposes." WBA 2019, p. 3. In the EU, 60% of all renewable energy comes from biomass. 75% of all biomass is used in the heating and cooling sector. See JRC 2019, p. 1.
^ "The International Energy Agency (IEA, 2012) defines traditional use of biomass as: '…the use of wood, charcoal, agricultural residues and animal dung for cooking and heating in the residential sector' and notes that 'it tends to have very low conversion efficiency (10% to 20%) and often relies on unsustainable biomass supply.'" IRENA 2014, p. 7.
^ ^a ^b "For example, limiting deployment of a mitigation response option will either result in increased climate change or additional mitigation in other sectors. A number of studies have examined limiting bioenergy and BECCS. Some such studies show increased emissions (Reilly et al. 2012). Other studies meet the same climate goal, but reduce emissions elsewhere via reduced energy demand (Grubler et al. 2018; Van Vuuren et al. 2018), increased fossil carbon capture and storage (CCS), nuclear energy, energy efficiency and/or renewable energy (Van Vuuren et al. 2018; Rose et al. 2014; Calvin et al. 2014; Van Vuuren et al. 2017b), dietary change (Van Vuuren et al. 2018), reduced non-CO₂ emissions (Van Vuuren et al. 2018), or lower population (Van Vuuren et al. 2018)." IPCC 2019e, p. 637.
^ "Biofuels are transportation fuels such as ethanol and biodiesel that are made from biomass materials." EIA 2021b.
^ In EU legislation, biofuel is defined as: "Liquid or gaseous fuel for transport produced from biomass." See European Commission 2018a.
^ "Some fast growing tree species can be cut down to a low stump (or stool) when they are dormant in winter and go on to produce many new stems in the following growing season. This practice is well established in the UK and Europe, having been a traditional method of woodland management over several hundred years for a variety of purposes including charcoal, fencing and shipbuilding." Forest Research 2022c.
^ "While short rotation coppicing (SRC) cuts the tree back to a stool to promote the growth of multiple stems, on a regular cycle of roughly 2-4 years, it is also possible to practice something more closely akin to conventional forestry, though on a shorter timescale. Short rotation forestry (SRF) consists of planting a site and then felling the trees when they have reached a size of typically 10-20 cm diameter at breast height. Depending on tree species this usually takes between 8 and 20 years, and is therefore intermediate in timescale between SRC and conventional forestry. This has the effect of retaining the high productivity of a young plantation, but increasing the wood to bark ratio." Forest Research 2022a.
^ "Woody energy crops: Short‐rotation plantings of woody biomass for bioenergy production, such as coppiced willow and miscanthus." IEA 2021b, p. 212.
^ "Estimates of marginal/degraded lands currently considered available for bioenergy range from 3.2–14.0 Mkm2, depending on the adopted sustainability criteria, land class definitions, soil conditions, land mapping method and environmental and economic considerations (Campbell et al. 2008; Cai et al. 2011; Lewis and Kelly 2014)." IPCC 2019c, p. 193.
^ "Plants convert CO₂ from the atmosphere into biomass. Carbon stored in biomass is called biogenic carbon. Some of this carbon stays above ground and some in the ground. When plants die, decomposition starts. As plant material decays, the stored carbon is released as CO₂ back into the atmosphere." IRENA 2014, p. 45.
^ "Wood from thinnings may, to some extent, be assimilated to harvest residues (especially pre-commercial thinnings). If not collected for bioenergy it would be left in the forest to decay, or combusted at roadside. On the other hand, depending on the wood quality, the use of thinnings wood for bioenergy may compete with other uses, such as pulp and paper or engineered wood. Salvage loggings can also be assimilated to harvest residues. Damaged, dying or dead trees affected by injurious agents, such as wind or ice storms or the spread of invasive epidemic forest pathogens, insects and diseases would remain in the forest and decay or combusted at roadside. Wood removed for prescribed fire hazard control as well can be considered residual wood." JRC 2014, pp. 42–43, table 3.
^ "This study estimated quantities of logging residues that can physically be recovered from harvest sites and utilized for electricity production in the US South. [...] Although almost all physically available logging residues could be recovered with a relatively short hauling distance, a mail survey indicated that only 4 percent of mills utilized this feedstock." Pokharel et al. 2019, p. 543.
^ "Currently, logging residue extraction, i.e., the harvest of tops and branches left during final felling, occurs on less than 20% of the harvested area in northern Sweden, and about 60% in southern Sweden. Stump harvest occurs to a limited extent today, but is expected to increase to about 5%–10% of the annual clear-felled area in the coming years. Similarly, logging residues constitute the main primary source of woody biofuels in most countries, but in the near future stumps and roundwood may play a more prominent role. Biofuel harvest from early thinnings in dense young forests are currently done to insignificant levels, but will increase, as for stumps, if prize levels rise. Therefore, there is considerable potential for increased extraction rates of primary woody biofuels, especially in northern Sweden, where current extraction rates are relatively low due to longer transport distances and lower harvestable volume per hectare compared to southern Sweden. The situation is similar in other European countries, with large un-used potentials for woody biomass for energy use." Eggers et al. 2020, p. 2.
^ "Logging residues are increasingly being extracted for bioenergy purposes." Dahlberg et al. 2011, p. 1220
^ van den Born et al. distinguish between logging residues in general and dead wood, with the logging residues potential at 14 EJ, and the dead wood potential at 1 EJ annually. For the logging residues potential, see van den Born et al. 2014, p. 20, table 4.2. Regarding the dead wood potential, the authors write: "A biomass pool is dead wood that remains in the forest, either standing or lying, and is transferred to the soil. It is often too costly to harvest dead wood. Besides, it is useful in increasing biodiversity (the proportion of dead wood is a sustainability criteria, (EEA, 2012). The global quantity of dead wood is estimated roughly at 67 Gt of biomass, which is about 11% of the total biomass (FAO, 2010), and about 20 times the annual wood harvest. [...] Dead wood: the global stock of dead wood is estimated at about 1200 EJ of biomass (FAO, 2010). This large pool has built up over a long period of time and in the entire forest area. Assuming an average rotation of 50 to 100 years, this implies a biomass pool of 10 to 20 EJ yr-1 [EJ per year]. When primary forests are excluded because they have not been used (based on FAO, 2010), about 7 to 14 EJ yr-1 of dead biomass remains. Forests with large quantities of dead wood are located in Russia and in parts of Africa. A limitation to the use of salvaged wood is the high costs of access and transport (Niquidet et al., 2012). A conservative estimate of accessible planted forests reduces the pool of available dead wood to about 2 EJ yr-1 biomass (Table 4.2). When an additional assumption is made that half of the dead wood needs to remain in forests to maintain biodiversity (Verkerk et al, 2012), the estimate is about 1 EJ yr-1 biomass available annually for energy production." (p. 15, 19-20)
^ "Biomass for bioenergy is usually a by-product of sawlog and pulpwood production for material applications (Dale et al., 2017; Ghaffariyan et al., 2017; Spinelli et al., 2019; Figure 1). Logs that meet quality requirements are used to produce high-value products such as sawnwood and engineered wood products such as cross laminated timber, which can substitute for more carbon-intensive building materials such as concrete, steel and aluminium (Leskinen et al., 2018). Residues from forestry operations (tops, branches, irregular and damaged stem sections, thinnings) and wood processing residues (e.g. sawdust, bark, black liquor) are used for bioenergy (Kittler et al., 2020), including to provide process heat in the forest industry (Hassan et al., 2019). These biomass sources have high likelihood of reducing net GHG emissions when substituting fossil fuels (Hanssen et al., 2017; Matthews et al., 2018), and their use for bioenergy enhances the climate change mitigation value of forests managed for wood production (Cintas, Berndes, Hansson, et al., 2017; Gustavsson et al., 2015, 2021; Schulze et al., 2020; Ximenes et al., 2012). Part of the forest biomass used for bioenergy consists roundwood (also referred to as stemwood), such as small stems from forest thinning. For example, roundwood was estimated to contribute around 20% of the feedstock used for densified wood pellets in the United States in 2018 (US EIA, 2019)." Cowie et al. 2021, pp. 1215–1216.
^ "The most crucial feedstock for the wood pellet sector is currently sawmill residues (85% of the mix), roundwood (13%), and recovered wood (2%). This mix is likely to change in the coming years with the forecasted expansion of the wood pellet industry. [...] Experience from North America shows that it is possible to use more forest residues as fiber furnish. Although it yields pellets with higher ash content, it is often a lower-cost raw material than, for example, roundwood and wood chips. This practice is increasingly common in both the US South (mainly for pellets exported to Europe) and Canada (mainly exported to Europe and Asia). In Western Canada, the sawmill residue share of the total feedstock has fallen from 97% in 2010 to 72% in 2020, with the balance being forest residues and roundwood." Wood Resources International 2022.
^ Recalculated from a total production of 43678925 tonnes wood pellets (FAO 2020), with 17 GJ/t energy content.
^ Recalculated from a total production of 265212933 m³ wood chips (FAO 2020), with 3.1 GJ/m³ energy content.
^ "In 2017, 55.6 EJ of biomass was utilized for energy purposes [...]. One of the most promising sectors for growth in bioenergy production is in the form of residues from agriculture sector. Currently, the sector contributes less than 3% to the total bioenergy production." WBA 2019, p. 3.
^ The Netherlands Environmental Assessment Agency estimated in 2014 that the total amount of agricultural residues amounts to 78 EJ, with 51 EJ from straw alone (pp. 12-13, table 3.4). "The large production of rice and the relatively low residue flow to the soil makes rice residues the residue with the highest potential for bioenergy, followed by residues from oilcrops, cereals, corn and sugarcane."(p. 19) Because a certain amount should be left in the fields for soil quality purposes, the total amount of agricultural residues that can be sustainably harvested amounts to 24 EJ. van den Born et al. 2014, pp. 2–21.
^ "One of the most promising sectors for growth in bioenergy production is in the form of residues from agriculture sector. Currently, the sector contributes less than 3% to the total bioenergy production. Data shows that utilizing the residues from all major crops for energy can generate approx. 4.3 billion tonnes (low estimate) to 9.4 billion tonnes (high estimate) annually around the world. Utilizing standard energy conversion factors, the theoretical energy potential from residues can be in the range of 17.8 EJ to 82.3 EJ. The major contribution would be from cereals – mainly maize, rice and wheat." WBA 2019, p. 3.
^ "At present, traditional methods of space heating and cooking, such as burning firewood, account for 35 EJ, or two-thirds of total biomass use. By 2030, this would give way to modern biomass consumption, including substantially larger shares for power and transport applications. Power and district heating would reach 36 EJ (one-third of total biomass use in 2030) and transport 31EJ (almost 29%), while heat for industry and buildings would reach up to 41 EJ, of which only 6 EJ would be from less sustainable traditional uses. While global biomass potential is sufficient to meet growing demand, different types of biomass resources are distributed unevenly. Global biomass supply potential in 2030 is estimated to range from 97 EJ to 147 EJ per year. Approximately 40% of this total would originate from agricultural residues and waste (37-66 EJ). The remaining supply potential is shared between energy crops (33-39 EJ) and forest products, including forest residues (24-43 EJ). In geographic terms, the largest supply potential — estimated at 43-77 EJ per year — exists in Asia and Europe. North and South America together account for another 45-55 EJ per year." IRENA 2021.
^ "Recent studies by Reza et al. and Smith et al. have reported of the fate of inorganics and heteroatoms during HTC [hydrothermal carbonisation] of Miscanthus and indicate significant removal of the alkali metals, potassium and sodium, along with chlorine. [...] Analysis of ash melting behaviour in Smith et al., showed a significant reduction in the slagging propensity of the resulting fuel, along with the fouling and corrosion risk combined. [...] Consequently HTC offers the potential to upgrade Miscanthus from a reasonably low value fuel into a high grade fuel, with a high calorific value, improved handling properties and favourable ash chemistry. [...] HTC at 250 °C can overcome slagging issues and increase the ash deformation temperature from 1040 °C to 1320 °C for early harvested Miscanthus. The chemistry also suggests a reduction in fouling and corrosion propensity for both 250 °C treated fuels." Smith et al. 2018, pp. 547, 556.
^ "A critical factor in the use of forest biomass in energy provision is the ‘payback time', during which atmospheric concentrations of carbon dioxide (CO₂) will be increased as a result of using biomass. EASAC concludes that the European Commission should consider the extent to which large-scale forest biomass energy use is compatible with UNFCCC targets (of limiting warming to 1.5 °C above pre-industrial levels), and whether a maximum allowable payback period should be set in its sustainability criteria." EASAC 2017, p. 2.
^ "The UK's plan to burn more trees to generate “renewable” electricity has come under fire from green groups and sustainable investment campaigners over the controversial claim that biomass energy is carbon-neutral. A letter to the government signed by more than a dozen green groups including Greenpeace and Friends of the Earth warns ministers against relying too heavily on plans to capture carbon emissions to help tackle the climate crisis. The plans are being pioneered by Drax Group, which claims that burning wood pellets is carbon-neutral because trees absorb as much carbon dioxide when they grow as they emit when they are burnt. Capturing the carbon emissions from biomass power plants would then effectively create “negative carbon emissions”, according to Drax. The green groups have disputed these claims and warned that the plans “will be costly” and “will not deliver negative emissions” after accounting for the full carbon footprint of biomass in the power sector." Ambrose 2021.
^ "By definition, clear-cutting trees and combusting their carbon emits greenhouse gases that heat up the earth. But policymakers in the U.S. Congress and governments around the world have declared that no, burning wood for power isn't a climate threat—it's actually a green climate solution. [...] [T]he [...] basic argument is that the carbon released while trees are burning shouldn't count because it's eventually offset by the carbon absorbed while other trees are growing. That is also currently the official position of the U.S. government, along with many other governments around the world. In documentaries, lawsuits and the teenage activist Greta Thunberg's spirited Twitter feed, critics of the industry have suggested an alternative climate strategy: Let trees grow and absorb carbon, then don't burn them. [...] Cutting down a tree and burning it clearly releases more carbon than leaving the tree alone; replanting the tree can only pay back the carbon debt in the long run, and an even longer run if the replanted tree is eventually reharvested. But biomass defenders say that focusing on one tree or even one clear-cut is far too narrow a way to think about forest carbon, because as long as the carbon absorbed by forests equals the carbon released from forests, the climate doesn't care. [...] The industry's position is that wood pellets actually help expand forests, by making it more lucrative for the private landowners who control most U.S. forest land to stay in the forestry business. The opponents argue that what wood pellets make more lucrative is deforestation. [...] “We can't say, ‘Oh, we can sacrifice forest over here, because it's growing over there. We need to stop sacrificing forest.” Grunwald 2021.
^ The IEA defines carbon neutrality and carbon negativity like so: "Carbon neutrality, or 'net zero,' means that any CO₂ released into the atmosphere from human activity is balanced by an equivalent amount being removed. Becoming carbon negative requires a company, sector or country to remove more CO₂ from the atmosphere than it emits."IEA 2020.
^ EU's Joint Research Centre defines "counterfactual" like so: "The impacts of each bioenergy pathway are evaluated against a counterfactual, i.e. a reference use of the biomass or of the land (thus the results should be interpreted as conditional to the chosen reference)." Camia et al. 2021, p. 83.
^ "It is important to notice that the definition of the reference system (both the energy system and the counterfactual biomass use) is as important as the definition of the bioenergy systems since the stated goal of the study is to assess the mitigation potential of the new systems as compared to the reference one." Camia et al. 2018, p. 100.
^ ^a ^b "Critical methodology decisions include the definition of spatial and temporal system boundaries [...] and reference (counterfactual) scenarios [...]. Focus on stack emissions (Option 1) neglects the key differences between fossil and biogenic carbon [...]. Focus on the forest only (Option 2) captures the effects of biomass harvest on forest carbon stocks [...] but omits the climate benefits of displacing fossil fuels. Option 3, the biomass supply chain, overlooks the interactions between biomass and other forest products [...]. Option 4 covers the whole bioeconomy, that is, the forest, the biomass supply chain and all bio-based products from managed forests, and thus provides a more complete assessment of the climate effects of forest bioenergy. In order to quantify the net climate effect of forest bioenergy, assessments should take a whole systems perspective. While this increases the complexity and uncertainty of the assessments, it provides a sound basis for robust decision-making. Biomass for bioenergy should be considered as one component of the bioeconomy (Option 4 [...]). Studies should therefore assess the effects of increasing biomass demand for bioenergy on carbon stocks of the whole forest, and also include the broader indirect impacts on emissions (potentially positive or negative) due to policy- and market-driven influences on land use, use of wood products and GHG-intensive construction materials, and fossil fuel use, outside the bioenergy supply chain. The bioenergy system should be compared with a realistic counterfactual(s) that includes the reference land use and energy systems [...]. This approach is consistent with consequential LCA [...]. The temporal boundary should recognize: forest carbon dynamics, for example, modelling over several rotations; the trajectory for energy system transition; and short- and long-term climate objectives. Matthews et al. (2018) suggest criteria that could be used to identify woody biomass with greater climate benefits when assessed from a full life cycle, whole system perspective." Cowie et al. 2021, pp. 1213, 1219–1220.
^ A simplified curve, complete with carbon payback and parity times, is available here: EASAC 2017, p. 23.
^ "The GWP is a measure of the effect of the pulse emission of a unit (mass) of a certain gas over its lifetime on the radiative properties of the atmosphere for a certain period of time. In the methodology designed by the IPCC [IPCC 2006], the GWP of CO₂- is taken as the reference value and assigned the value of 1. The reasoning of the authors is that biogenic CO₂- has indeed the same radiative effect of fossil CO₂ on the atmosphere but, while fossil CO₂- can only be reabsorbed by oceans and biosphere (according to the formulation using Bern CC equation, as given by [IPCC 2006]), biogenic-CO₂- has an additional factor which is the reabsorption of the CO₂- via re-growth of vegetation on the same piece of land. By this mathematical formulation, they have been able to assign various values of a so-called GWP_bio- over the typical time horizons of 20, 100 and 500 years and depending on the timing of biomass re-growth. Technically, this factor can then be simply used in a classical LCA and applied as correction factor to the amount of the biogenic-CO₂ emitted by the combustion of biomass." JRC 2014, p. 45.
^ "Annualised emissions from carbon stock changes caused by land-use change, e_l, shall be calculated by dividing total emissions equally over 20 years." European Parliament, Council of the European Union 2018, p. Annex VI.
^ See for instance the European Union's official emission savings percentages for different fuels here: European Parliament, Council of the European Union 2018, p. ANNEX VI. Note that these estimates do not include the average net emissions which results from an eventual land use change prior to planting.
^ "The Renewable Energy Directive (RED), as well as the Fuel Quality Directive (FQD) and the proposal for a RED-Recast (EP 2009, EP 2009b and EC 2016) apply a simplified attributional LCA methodology to assess GHG emissions savings for a series of liquid biofuels pathways used in the transport sector. A similar methodology is also extended to biomass used for power, heat and cooling generation (EC 2016). The RED evaluates the supply-chains GHG emissions of various bioenergy pathways and compares them to each other on a common basis (GHG emission savings with respect to a fossil fuel comparator) to promote the pathways that perform best on this relative scale and to exclude the pathways with the worst technologies and GHG performances." Camia et al. 2018, p. 89.
^ "Two main modelling principles are in use in LCA practice: Attributional (A-LCA) and Consequential (C-LCA) modelling, with the former being more widely used for historical and practical reasons. [...] Attributional modelling makes use of historical, fact-based, average, measureable data of known (or at least knowable) uncertainty, and includes all the processes that are identified to relevantly contribute to the system being studied. In attributional modelling, the system is hence modelled “as it is” or “as it was” (or as it is forecasted to be) (EC, 2010). Attributional modelling is also referred to as “accounting”, “book-keeping”, “retrospective”, or “descriptive”. [...] [P]urely attributional LCA studies of bioenergy systems are unable to capture properly all of the complexities linking bioenergy, climate, bioenergy and ecosystem services (e.g. market-mediated effects, biogeophysical, time-dependent effects). [...] The results of these types of assessment are static in time and do not account for biogenic-C flows. It has become established practice in A-LCA to assume that any emission of biogenic CO₂ (release to the atmosphere of the carbon contained in biological resources) is compensated by photosynthesis during the re-growth of the biomass feedstock. This assumption originates from an interpretation of the rules for reporting national GHG inventories to the United Nations Framework Convention on Climate Change (UNFCCC). Biogenic-C flow are accounted for in the land use, land-use change, and forestry (LULUCF) chapter at the time the biomass commodity is harvested and are therefore not accounted for in the energy sector at the time the biomass is burnt (JRC, 2013). It remains valid for system-level analysis, when the changes in biomass carbon stocks are accounted in the land-use sector rather than in the energy sector (EC, 2016c)." Camia et al. 2018, pp. 89–91.
^ "Bioenergy from dedicated crops are in some cases held responsible for GHG emissions resulting from indirect land use change (iLUC), that is the bioenergy activity may lead to displacement of agricultural or forest activities into other locations, driven by market-mediated effects. Other mitigation options may also cause iLUC. At a global level of analysis, indirect effects are not relevant because all land-use emissions are direct. iLUC emissions are potentially more significant for crop-based feedstocks such as corn, wheat and soybean, than for advanced biofuels from lignocellulosic materials (Chum et al. 2011; Wicke et al. 2012; Valin et al. 2015; Ahlgren and Di Lucia 2014). Estimates of emissions from iLUC are inherently uncertain, widely debated in the scientific community and are highly dependent on modelling assumptions, such as supply/demand elasticities, productivity estimates, incorporation or exclusion of emission credits for coproducts and scale of biofuel deployment (Rajagopal and Plevin 2013; Finkbeiner 2014; Kim et al. 2014; Zilberman 2017). In some cases, iLUC effects are estimated to result in emission reductions. For example, market-mediated effects of bioenergy in North America showed potential for increased carbon stocks by inducing conversion of pasture or marginal land to forestland (Cintas et al. 2017; Duden et al. 2017; Dale et al. 2017; Baker et al. 2019). There is a wide range of variability in iLUC values for different types of biofuels, from –75–55 gCO₂ MJ–1 (Ahlgren and Di Lucia 2014; Valin et al. 2015; Plevin et al. 2015; Taheripour and Tyner 2013; Bento and Klotz 2014). There is low confidence in attribution of emissions from iLUC to bioenergy." IPCC 2019i, p. 194.
^ One often cited example of indirect land use change is the land use change from forest to agriculture that happened in Brazil after the US started to use some of its harvested corn for ethanol production rather than animal feed. The resulting lower supply of animal feed on the global market was seen as an opportunity by Brazilian farmers, who subsequently cut down forests in order to plant soya beans destined for the animal feed market. See Bird et al. 2010, p. 5, and also Searchinger et al. 2008, pp. 1238–1240 for the original research article.
^ According to Nabuurs et al., displacement factors takes into consideration the difference in CO₂ emissions per unit of primary energy produced, differences in efficiency of energy conversion (e.g. conversion from primary energy to electricity) and in some cases also the emission differences in the supply chains. See Nabuurs, Arets & Schelhaas 2017, p. 4. See also Cowie et al. 2021, p. 1214.
^ "Wood and coal have similar CO₂ emission factors, as the ratio of heating values between the two fuels is similar to the ratio of carbon content [...]. Where biomass is co-fired with coal in large power plants, the conversion efficiency may decrease a few percent, although there is usually no significant efficiency penalty when the co-firing ratio is below 10% [...]. Conversion efficiencies depend on fuel properties including moisture content and grindability in addition to heating value [...]. For low rank coal, biomass co-firing (especially torrefied biomass) can increase the boiler efficiency and net power plant efficiency [...]. Smaller biomass-fired plants can have lower electric conversion efficiency than large coal-fired plants, but as they are typically combined heat and power plants, they also displace heat production from other sources, that could otherwise have generated fossil fuel emissions [...]. Large dedicated biomass units (converted from coal) can operate with roughly the same level of thermal efficiency as delivered historically from coal [...]. Cowie et al. 2021, p. 1214.
^ "Bioenergy with carbon capture and storage (BECCS) plays a critical role in the NZE Scenario by offsetting emissions from sectors where full decarbonisation is extremely difficult to achieve. In 2050, around 10% of total bioenergy is used in facilities equipped with carbon capture, utilisation and storage, and around 1.3 billion tonnes of CO₂ is captured using BECCS. Around 45% of this CO₂ is captured in biofuels production, 40% in the electricity sector, and the rest in heavy industry, notably cement production." IEA 2021a.
^ "In case that there is no raw material displacement from other sectors such as food, feed, fibers or changes in land carbon stocks due to direct or indirect land use change, the assumption of carbon neutrality can still be considered valid for annual crops, agriresidues, short-rotation coppices and energy grasses with short rotation cycles. This can also be valid for analysis with time horizons much longer than the feedstock growth cycles. [...] The timeframe of the comparison too plays a relevant role in the performances of the reference system. If the timeframe chosen is short, the current emissions from the reference system can be considered appropriate and constant. In the case of a long-term analysis, though, also the changes in the fossil reference system have to be accounted for. For instance, practically in all of the studies analyzed the reference system (coal or NG) is kept constant and unchanged for the whole duration of the analysis (even centuries), while, according to EU policies, by 2050 the EU should be decarbonized, implying that future savings might be much smaller than current ones. In this case [...] it may happen that the payback time is never reached. [...] On the other hand, if the reference fossil system gets ‘dirtier', as in the case of most of the unconventional fossil energy (shale gas, bituminous coal etc.) the fossil fuel parity may be reached sooner than with a constant reference fossil fuel." JRC 2014, pp. 23, 51–52. Note that the JRC use the term "payback time" in the sense of "parity time" as defined in Carbon accounting principles above. See JRC 2014, p. 16.
^ "Studies of real forest landscapes show that the net GHG effects of bioenergy incentives are more variable than suggested by studies that do not consider economic factors and varying conditions in the forest and wood products sector." Cowie et al. 2021, p. 1218.
^ EU's Joint Research Centre describes how the economic boundaries can expand to reach macro-economic size: "Large scale techno-economic modeling: This type of analysis includes a macroeconomic model that estimates the developments of the wood market in terms of imports, quantity of wood used for wood products and for bioenergy etc. as response to a given decision. The market model is coupled with a forest model that can model changes in carbon stocks in all the pools of forests (including living and dead wood, soil-C etc.) and eventually the carbon stocked in wood products. These two models can then be combined with several scenarios for the substitution of wood products in which a typical LCA (biogenic-CO₂ emissions are set to zero) is applied to calculate the GHG savings due to the use of biomass compared to the alternative materials / feedstocks. The combination of these calculations would provide a clear and quantitative forecast of possible carbon savings or emissions due to different policy scenarios and over different time horizons." JRC 2014, p. 69.
^ See for instance Camia et al. 2021, pp. 86, 100.
^ "Wide variation in published estimates of payback time for forest bioenergy systems reflects both inherent differences between these systems and different methodology choices [...]. Critical methodology decisions include the definition of spatial and temporal system boundaries [...] and reference (counterfactual) scenarios [...]. Misleading conclusions on the climate effects of forest bioenergy can be produced by studies that focus on emissions at the point of combustion, or consider only carbon balances of individual forest stands, or emphasize short-term mitigation contributions over long-term benefits, or disregard system-level interactions that influence the climate effects of forest bioenergy." Cowie et al. 2021, pp. 1213, 1221.
^ Jonker et al. examined the carbon intensity for southeastern forests in the US, and concluded that due to the large number of possible methodological choices and reference systems, the calculations produce a wide range of payback and parity times, from below 1 year payback time with landscape level carbon accounting to 27 years with stand level accounting, and parity times of 2 –106 years depending on system boundaries and the choice of alternative scenarios. The authors consider landscape-level carbon accounting more appropriate for the examined situation. Under this precondition, the issue of carbon payback time is basically nonexistent. If comparison against a protection scenario is deemed realistic and policy relevant, and assuming that wood pellets directly replace coal in an average coal power plant, the carbon parity time is 12–46 years; i.e. one or two rotations. Switching to intensively managed plantations yields the most drastic reduction in parity time (below 18 years in 9 of 12 cases). The authors conclude that the choice of carbon accounting method has a significant impact on the carbon payback and parity times. Jonker, Junginger & Faaij 2013, pp. 371–387.
^ "Studies reporting long carbon debt payback times in general assume that the biomass is utilized for electricity production with low conversion efficiencies and that the woody biomass originates from the dedicated harvest of trees for energy from long rotation forestry. Looking at the current use of bioenergy in the EU, there is little evidence that such supply chains dominate." Madsen & Bentsen 2018, p. 1.
^ "Misleading conclusions on the climate effects of forest bioenergy can be produced by studies that focus on emissions at the point of combustion, or consider only carbon balances of individual forest stands, or emphasize short-term mitigation contributions over long-term benefits, or disregard system-level interactions that influence the climate effects of forest bioenergy. Payback time calculations are influenced by subjective methodology choices and do not reflect the contribution of bioenergy within a portfolio of mitigation measures, so it is neither possible nor appropriate to declare a generic value for the maximum acceptable payback time for specific forest bioenergy options. To answer the key question ‘what are the climate implications of policies that promote bioenergy?' assessment should be made at the landscape level, and use a full life cycle approach that includes supply chain emissions, changes in land carbon stocks and other variables influenced by the policies studied. Effects on land cover, land management and the wood products and energy sectors need to be considered, including indirect impacts at international level. The bioenergy system should be compared with reference scenarios (counterfactuals) that describe the most likely alternative land use(s) and energy sources that would be displaced by the bioenergy system, and the probable alternative fates for the biomass being utilized. A no-harvest counterfactual is not realistic in most current circumstances, but markets that pay for carbon sequestration and other ecosystem services could change incentives for harvest in the future."Cowie et al. 2021, pp. 1221–1222.
^ Bentsen examined 245 individual studies and found that the carbon payback time of apparently comparable forest bioenergy supply scenarios vary by up to 200 years, which provides ample room for confusion and dispute about the climate benefits of forest bioenergy. He concludes that the outcome of carbon debt studies lie in the assumptions, and that methodological rather than ecosystem and management related assumptions determine the findings. The findings are therefore seen as inadequate for informing and guiding policy development. Bentsen 2017, p. 1211.
^ "There is a large variability in the literature results for fossil fuel parity times. This is due to differences in the characteristics of the forest system considered (growth rate, management), in the carbon pools included, in the system boundaries definition and in the reference baseline used in the analysis." JRC 2014, p. 75.
^ EU's Joint Research Centre recommend that "[...] policymakers and scientists alike recognize that diverging values, worldviews, and ethical perceptions of natural resources and their management are a core part of the debate. These will not be solved by more scientific research, because science is a social endeavour where value-choices and judgements are inevitable. Transparency is key and cooperation with policymakers and co-creation of useful results should be welcomed." Camia et al. 2021, p. 93. In a presentation of this report for IEA Bioenergy, the JRC staff expand on this conclusion. They write that the question “Does forest bioenergy mitigate climate change?” really has no answer, as it is depends on "modelling approaches and the assumptions about hypothetical futures", and that researchers "come to equally valid, but opposite answers depending on assumptions chosen." They also write that "the assumptions chosen will align (consciously or unconsciously) with the worldviews and ethical values of the authors." According to the JRC, supporters of bioenergy usually have a more anthropocentric view of the human-nature relationship, while opposers of bioenergy are more aligned with nature conservation values. These norms lead to different concerns and definitions of what sustainability really is. See Mubareka, Giuntoli & Grassi 2021, pp. 8–9.
^ "Most of the forest feedstocks used for bioenergy, as of today, are industrial residues, waste wood, residual wood (thinnings, harvest residues, salvage loggings, landscape care wood etc.) for which, in the short to medium term, GHG savings may be achieved. On the other hand, in the case of stemwood harvested for bioenergy purposes only, if all the carbon pools and their development with time are considered in both the bioenergy and the reference fossil scenario, there is an actual increase in CO₂ emissions compared to fossil fuels in the short-term (few decades). In the longer term (centuries) also stemwood may reach the fossil fuel parity points and then generate GHG savings if the productivity of the forest is not reduced because of bioenergy production. [...] The results attained are strongly correlated with the following parameters: the fossil fuel replaced, efficiency of the biomass utilization, the future growth rate of the forest, the frequency and intensity of biomass harvests and the initial landscape carbon stock." JRC 2014, p. 75.
^ "Increased removal of FWD [fine woody debris], low stumps, CWD (course woody debris): It depends strongly on the decay rates considered. For instance, (Giuntoli et al., 2015) and (Giuntoli et al., 2016) found that residues with decay rates of 11.5%/year would mitigate climate change compared to natural gas heating and natural gas electricity after about 20 years, but residues with decay rate lower than 2.7%/year would take more than 86 years to payback compared to natural gas heating, or more than a century compared to the current EU power mix. FWD are thus likely to achieve carbon mitigation in a short term. However, decay rates for low stumps have been reported to range between 0.7%/year up to even 11%/year (Persson and Egnell, 2018), depending on climatic conditions and species. Considering a representative decay rate for temperate/boreal forests of between 3 and 6%/year would mean stumps would be unlikely to achieve climate mitigation before 50 years. This is substantiated also by the work of (Laganière et al., 2017). However, we indicate a range of uncertainty across other climate change levels. CWD are very likely to exhibit low decay rates and to have very long payback times." Camia et al. 2021, p. 143. See also JRC 2014, pp. 16–17, 43–44.
^ Lamers & Junginger examined a number of studies and argue that parity times for residues "[...] mostly vary depending on the respective fossil fuel used in the reference scenario [...]." However, the second most important influencing factor "[...] is the size/diameter of the residue and the forest biome, i.e. conditions affecting the decay rate." The shortest parity times were found for forest residues which would otherwise be burned at the factory or roadside. This immediate carbon release in the alternative scenario causes an immediate carbon benefit and a net zero parity time for the bioenergy scenario. The longest parity times were for stump harvest in the cold boreal forests of northern Finland, when compared to a natural decay scenario for the stumps, and instead production of electricity from natural gas. For stemwood, parity times vary to some degree by forest biome with significantly shorter periods for highly productive regions, such as the temperate moist forests of the South-Eastern USA. In the boreal or sub-boreal forests, parity times against a forest protection scenario are about twice as large, but there are variations between studies. Under specific conditions, for instance where insect infestation has killed a large amount of merchantable timber stock, "[...] bioenergy harvest can reach parity times as low a zero." The high share of fast decaying tree biomass in the protection scenario shortens parity times. Parity times against regular timber harvest (business as usual) vary greatly with the fossil fuel alternative scenario, the shortest being coal and oil compared to natural gas. Afforestation on the other hand has a parity time of zero years if the land area in question would not be sequestering large amounts of carbon otherwise. Lamers & Junginger 2013, p. 379.
^ "There is a large variability in the results of forest bioenergy fossil fuel parity times calculations. This large variability depends on the many different characteristics of the systems compared and non-consistent modeling assumptions and approaches. The first, most important assumption is on the fossil fuel displaced. Then, concerning both the bioenergy system and the reference fossil system the following characteristics heavily impact the results: efficiency in the final use, future growth rate of the forest, the frequency and intensity of biomass harvests, the initial forest carbon stock, the forest management practices assumed." JRC 2014, p. 17.
^ "The reviewed studies show payback times ranging from 0 to almost 500 years. This large variability depends on the many different characteristics and assumptions on both the forest/bioenergy system and the reference fossil system. The most straight forward relation is with the fossil fuel used as a reference in the fossil scenario. Obviously, the more carbon intensive the fossil fuel replaced is, the shorter is the payback time. [...] A further correlation exists with the efficiency of the biomass utilization. The less efficient the bioenergy system is, the longer are the payback times. In case of electricity production, in biomass only plants, the electrical efficiency of biomass conversion is lower than the fossil, while thermal conversion energetic efficiency is similar for biomass and fossil fuels. In co-firing plants, biomass generally achieves the same efficiency as coal. An intensive processing, such as for liquid biofuel substitution via lignocellulosic ethanol, causes much longer payback times because of the loss of energy in the biofuels production (about half of the energy content of the biomass is lost in the processing [...]. The slower the forest growth rate is, the longer is the payback time. The forest growth rate depends on the latitude (boreal, temperate, tropical), but also on specific characteristics of the trees species, the microclimate and the soil fertility." JRC 2014, p. 34. Note that the JRC use the term "payback time" in the sense of "parity time" as defined in Carbon accounting principles above. See JRC 2014, p. 16.
^ See Hanssen et al. 2017: Figure S3 at page 3 in the Supporting Information document, link to document available at the bottom of the article.)
^ "In addition to the EU, the US has also amended its Renewables Fuel Standard 1 (RFS1) to include minimum life-cycle GHG emissions in the RFS2. RFS2 distinguishes between the production of conventional and advanced biofuels, which are defined based on their GHG abatement potential. All biofuels which can save up to 20% GHG in their life cycle compared to the petroleumbased equivalents are categorised as conventional. Conventional biofuel production is limited to 15 billion gallons to 2022. Advanced biofuels production accounts for the remainder 21 billion gallons. A biofuel can be considered advanced if it saves at least 50% GHG. Cellulosic biofuels require a 60% GHG emission reduction compared to the petrochemical equivalent (EPA, 2012). These emissions include ILUC GHG emissions." IRENA 2014, p. 47.
^ The estimates are for the "medium case" considered (case 2a); a pellet mill that uses wood for processing heat, but sources electricity from the grid. Estimates (for forest residue based pellets) reduce to 50–58% when fossil fuels is used for processing heat (case 1), but increase to 84-92% when electricity is sourced from a CHP biomass power plant (case 3a). See European Parliament, Council of the European Union 2018, p. Annex VI.
^ "Any soil disturbance, such as ploughing and cultivation, is likely to result in short-term respiration losses of soil organic carbon, decomposed by stimulated soil microbe populations (Cheng, 2009; Kuzyakov, 2010). Annual disturbance under arable cropping repeats this year after year resulting in reduced SOC levels. Perennial agricultural systems, such as grassland, have time to replace their infrequent disturbance losses which can result in higher steady-state soil carbon contents (Gelfand et al., 2011; Zenone et al., 2013)." McCalmont et al. 2017, p. 493.
^ "Tillage breaks apart soil aggregates which, among other functions, are thought to inhibit soil bacteria, fungi and other microbes from consuming and decomposing SOM (Grandy and Neff 2008). Aggregates reduce microbial access to organic matter by restricting physical access to mineral-stabilised organic compounds as well as reducing oxygen availability (Cotrufo et al. 2015; Lehmann and Kleber 2015). When soil aggregates are broken open with tillage in the conversion of native ecosystems to agriculture, microbial consumption of SOC and subsequent respiration of CO₂ increase dramatically, reducing soil carbon stocks (Grandy and Robertson 2006; Grandy and Neff 2008)." IPCC 2019a, p. 393.
^ "In 2015, a workshop was convened with researchers, policymakers and industry/business representatives from the UK, EU and internationally. Outcomes from global research on bioenergy land‐use change were compared to identify areas of consensus, key uncertainties, and research priorities. [...] Our analysis suggests that the direct impacts of dedicated perennial bioenergy crops on soil carbon and nitrous oxide are increasingly well understood and are often consistent with significant life cycle GHG mitigation from bioenergy relative to conventional energy sources. We conclude that the GHG balance of perennial bioenergy crop cultivation will often be favourable, with maximum GHG savings achieved where crops are grown on soils with low carbon stocks and conservative nutrient application, accruing additional environmental benefits such as improved water quality. The analysis reported here demonstrates there is a mature and increasingly comprehensive evidence base on the environmental benefits and risks of bioenergy cultivation which can support the development of a sustainable bioenergy industry." Whitaker et al. 2018, p. 150.
^ Hektor et al. argue that flue gas condensation devices combined with natural drying of biomass makes it possible to achieve similar or better combustion efficiency than coal: "When burning moist biomass, energy is 'lost' in the evaporation of water. However, modern technology makes it possible to recover a large portion of that energy by flue gas condensation devices." The author also recommends "[...] simpler measures, such as natural drying [...]", and argue that "[...] state-of-the art technologies are nowadays generally included in new applications of biomass energy [...]" and that "[...] taking these factors into consideration, biomass would have about the same gross CO₂ emissions per generated amount of energy as coal [...]." Hektor, Backéus & Andersson 2016, p. 4. See also OECD/IEA 2004, p. 20.
^ The individual emission rates are: Wood 112 000 kg CO₂eq per TJ, anthracite 98 300, coking coal 94 600, other bituminous 94 600, sub-bituminous 96 100, lignite 101 000. IPCC 2006a, pp. 2.16–2.17.
^ "Estimating gross emissions only, creates a distorted representation of human impacts on the land sector carbon cycle. While forest harvest for timber and fuelwood and land-use change (deforestation) contribute to gross emissions, to quantify impacts on the atmosphere, it is necessary to estimate net emissions, that is, the balance of gross emissions and gross removals of carbon from the atmosphere through forest regrowth [...]." IPCC 2019a, p. 368.
^ "It is incorrect to determine the climate change effect of using biomass for energy by comparing GHG emissions at the point of combustion [...] the misplaced focus on emissions at the point of combustion blurs the distinction between fossil and biogenic carbon, and it prevents proper evaluation of how displacement of fossil fuels with biomass affects the development of atmospheric GHG concentrations." IEA Bioenergy 2019, pp. 3–4.
^ "The trends of productivity shown by several remote-sensing studies (see previous section) are largely consistent with mapping of forest cover and change using a 34-year time series of coarse resolution satellite data (NOAA AVHRR) (Song et al. 2018). This study, based on a thematic classification of satellite data, suggests that (i) global tree canopy cover increased by 2.24 million km² between 1982 and 2016 (corresponding to +7.1%) but with regional differences that contribute a net loss in the tropics and a net gain at higher latitudes, and (ii) the fraction of bare ground decreased by 1.16 million km² (corresponding to –3.1%), mainly in agricultural regions of Asia (Song et al. 2018), see Figure 4.5. Other tree or land cover datasets show opposite global net trends (Li et al. 2018b), but high agreement in terms of net losses in the tropics and large net gains in the temperate and boreal zones (Li et al. 2018b; Song et al. 2018; Hansen et al. 2013)." IPCC 2019a, p. 367.
^ "Second, our findings are similarly compatible with the well-known age-related decline in productivity at the scale of even-aged forest stands. [...] We highlight the fact that increasing individual tree growth rate does not automatically result in increasing stand productivity because tree mortality can drive orders-of-magnitude reductions in population density. That is, even though the large trees in older, even-aged stands may be growing more rapidly, such stands have fewer trees. Tree population dynamics, especially mortality, can thus be a significant contributor to declining productivity at the scale of the forest stand." Stephenson et al. 2014, p. 3.
^ "SFM [sustainable forest management] applied at the landscape scale to existing unmanaged forests can first reduce average forest carbon stocks and subsequently increase the rate at which CO₂ is removed from the atmosphere, because net ecosystem production of forest stands is highest in intermediate stand ages (Kurz et al. 2013; Volkova et al. 2018; Tang et al. 2014). The net impact on the atmosphere depends on the magnitude of the reduction in carbon stocks, the fate of the harvested biomass (i.e. use in short – or long-lived products and for bioenergy, and therefore displacement of emissions associated with GHG-intensive building materials and fossil fuels), and the rate of regrowth. Thus, the impacts of SFM on one indicator (e.g., past reduction in carbon stocks in the forested landscape) can be negative, while those on another indicator (e.g., current forest productivity and rate of CO₂ removal from the atmosphere, avoided fossil fuel emissions) can be positive. Sustainably managed forest landscapes can have a lower biomass carbon density than unmanaged forest, but the younger forests can have a higher growth rate, and therefore contribute stronger carbon sinks than older forests (Trofymow et al. 2008; Volkova et al. 2018; Poorter et al. 2016)." IPCC 2019a, p. 351.
^ "Bioenergy provides only 5% of total electricity generation in 2050, but it is an important source of low-emissions flexibility to complement variable generation from solar PV and wind. In the industry sector, where solid bioenergy demand reaches 20 EJ in 2050, it is used to meet high temperature heat needs that cannot be easily electrified such as paper and cement production. In 2050, bioenergy meets 60% of energy demand in the paper sector and 30% of energy demand for cement production." IEA 2021a.
^ The IEA estimates that replacing short rotation coppice forests with hydrogen production (for heat processing purposes) would cost 4.5 trillion USD: "The additional wind, solar, battery and electrolyser capacity, together with the electricity networks and storage needed to support this higher level of deployment would cost more than USD 5 trillion by 2050. This is USD 4.5 trillion more than would be needed if the use of bioenergy were to be expanded as envisaged in the NZE [Net Zero Emissions scenario], and would increase the total investment needed in the NZE by 3%. While it might therefore be possible still to achieve net‐zero emissions in 2050 without expanding land use for bioenergy, this would make the energy transition significantly more expensive. " IEA 2021b, p. 94.
^ "The potentially very long payback periods for forest biomass raise important issues given the UNFCCC's aspiration of limiting warming to 1.5 °C above preindustrial levels to ‘significantly reduce the risks and impacts of climate change'. On current trends, this may be exceeded in around a decade. Relying on forest biomass for the EU's renewable energy, with its associated initial increase in atmospheric carbon dioxide levels, increases the risk of overshooting the 1.5°C target if payback periods are longer than this. The European Commission should consider the extent to which large-scale forest biomass energy use is compatible with UNFCCC targets and whether a maximum allowable payback period should be set in its sustainability criteria." EASAC 2017, p. 34.
^ The forest landscape works as a proxy for calculating specifically human GHG emissions: "In the AFOLU [Agriculture, Forestry and Other Land Use] sector, the management of land is used as the best approximation of human influence and thus, estimates of emissions and removals on managed land are used as a proxy for anthropogenic emissions and removals on the basis that the preponderance of anthropogenic effects occurs on managed lands (see Vol. 4 Chapter 1). This allows for consistency, comparability, and transparency in estimation. Referred to as the Managed Land Proxy (MLP), this approach is currently recognised by the IPCC as the only universally applicable approach to estimating anthropogenic emissions and removals in the AFOLU sector (IPCC 2006, IPCC 2010)." IPCC 2019j, p. 2.67.
^ "The natural disturbance component is subtracted from the total estimate of [...] emissions and removals, yielding an estimate of the emissions and removals associated with human activity on managed land." See IPCC 2019j, p. 2.72. "The 2006 IPCC Guidelines are designed to assist in estimating and reporting national inventories of anthropogenic greenhouse gas emissions and removals. For the AFOLU Sector, anthropogenic greenhouse gas emissions and removals by sinks are defined as all those occurring on ‘managed land'. Managed land is land where human interventions and practices have been applied to perform production, ecological or social functions. [...] This approach, i.e., the use of managed land as a proxy for anthropogenic effects, was adopted in the GPG–LULUCF and that use is maintained in the present guidelines. The key rationale for this approach is that the preponderance of anthropogenic effects occurs on managed lands. By definition, all direct human-induced effects on greenhouse gas emissions and removals occur on managed lands only. While it is recognized that no area of the Earth's surface is entirely free of human influence (e.g., CO₂ fertilization), many indirect human influences on greenhouse gases (e.g., increased N deposition, accidental fire) will be manifested predominately on managed lands, where human activities are concentrated. Finally, while local and short-term variability in emissions and removals due to natural causes can be substantial (e.g., emissions from fire, see footnote 1), the natural ‘background' of greenhouse gas emissions and removals by sinks tends to average out over time and space. This leaves the greenhouse gas emissions and removals from managed lands as the dominant result of human activity. Guidance and methods for estimating greenhouse gas emissions and removals for the AFOLU Sector now include: • CO₂ emissions and removals resulting from C stock changes in biomass, dead organic matter and mineral soils, for all managed lands; • CO₂ and non-CO₂ emissions from fire on all managed land; • N₂O emissions from all managed soils; • CO₂ emissions associated with liming and urea application to managed soils; • CH4 emissions from rice cultivation; • CO₂ and N₂O emissions from cultivated organic soils; • CO₂ and N₂O emissions from managed wetlands (with a basis for methodological development for CH4 emissions from flooded land in an Appendix 3); • CH4 emission from livestock (enteric fermentation); • CH4 and N₂O emissions from manure management systems; and • C stock change associated with harvested wood products." See IPCC 2006b, p. 1.5.
^ "Limitations on bioenergy and BECCS can result in increases in the cost of mitigation (Kriegler et al. 2014; Edmonds et al. 2013). Studies have also examined limiting CDR, including reforestation, afforestation, and bioenergy and BECCS (Kriegler et al. 2018a,b). These studies find that limiting CDR can increase mitigation costs, increase food prices, and even preclude limiting warming to less than 1.5°C above pre-industrial levels (Kriegler et al. 2018a,b; Muratori et al. 2016)." IPCC 2019e, p. 638.
^ "Concern about near-term emissions is not a strong argument for stopping investments that contribute to net emissions reduction beyond 2030, be it the scaling-up of battery manufacturing to support electrification of car fleets, the development of rail infrastructure, or the development of biomass supply systems and innovation to provide biobased products displacing fossil fuels, cement and other GHG-intensive products. We assert that it is critical to focus on the global emissions trajectory required to achieve climate stabilization, acknowledging possible trade-offs between short- and long-term emissions reduction objectives. A strong focus on short-term carbon balances may result in decisions that make long-term climate objectives more difficult to meet."IEA Bioenergy 2019, p. 4.
^ "Pathways in the first and fourth quadrants are relatively clear situations in which trade-offs are not evident, and should thus clearly be a target for governance measures; in the sense that pathways in quadrant 1 should be incentivised, while pathways in quadrant 4 should be discouraged. Forest bioenergy pathways which fit within the first quadrant are the ones that are very likely to contribute to climate change mitigation in a short-medium term, and at the same time are likely to improve the condition of local ecosystems and biodiversity (or at least do not affect paths of ecosystem restoration). Pathways in the fourth quadrant are the ones that are unlikely to contribute to climate change mitigation in the short-medium term and at the same time are likely to further degrade ecosystems' condition. Conversely, pathways in quadrants 2 and 3 are the ones for which trade-offs between climate mitigation and biodiversity can be identified or assumed. Pathways in quadrant 2 are the ones that even though they are likely to mitigate climate change, they are also likely to negatively impact local biodiversity. For these pathways, safeguards or mitigation strategies should be investigated, and if available, should be considered mandated as contingent to the promotion of bioenergy. This case is also the only case in which the trade-off mentioned above (global climate change mitigation vs. local degradation) could influence the final evaluation of the pathway. Pathways in the third quadrant are likely to improve local ecosystem condition, but might not mitigate climate change in the short term. In these cases, bioenergy production might be seen as a by-product of restoration operations. In both cases in quadrants 2 & 3, trade-offs that cannot be resolved will need to be weighted and discussed during the decision-making process." Camia et al. 2021, p. 107.
^ "Win-win management practices that benefit climate change mitigation and have either a neutral or positive effect on biodiversity include removal of slash (fine, woody debris) below thresholds defined according to local conditions, and afforestation of former arable land with mixed forest or naturally regenerating forests. [...] [C]oppice forests are particularly important in Mediterranean countries, they provide many ecosystem services, have relevant socio-economic functions in many rural areas and are mainly utilised for bioenergy. However, in large areas coppices are no longer managed or completely abandoned, resulting in old or overgrown declining stands. In these cases, it is suggested to encourage active forest management, that would enhance the capacity of these ecosystems to store carbon and supply services. Depending on local considerations the preferred option could be active conversion to high forest, or coppice restoration (see Section 5.9.2). [...] [W]e find that collecting slash within the limits of locally recommended thresholds could generate energy without damaging forest ecosystems and at the same time likely contributing to reducing GHG emissions. Similarly, afforesting former agricultural land with mixed species plantations or with naturally regenerating forests would enhance the terrestrial sink even before producing biomass for energy and thus would contribute to climate change mitigation, while at the same time improving ecosystems' conditions. [...] Collecting slash within the limits of locally recommended thresholds could be used to generate energy without damaging forest ecosystems while likely contributing to reducing GHG emissions. Afforesting former agricultural land with mixed species plantations or with naturally regenerating forests would enhance the terrestrial sink even before producing biomass for material and energy uses and thus would contribute to climate change mitigation, while at the same time improving ecosystems' conditions. [...] [C]ollection and use of low stumps within locally established thresholds in climate areas with high decay rates could potentially provide carbon emissions mitigation without damaging local biodiversity; local conditions should be evaluated in these cases." Camia et al. 2021, pp. 8–149.
^ "Although not extensively captured in the case studies, there is clear consensus in the literature that afforestation of primary, ancient grassland ecosystems which were never forests, may have very detrimental effects on local biodiversity; some authors compare these effects to the destructive effects of deforestation (Abreu et al., 2017; Bond, 2016; Bond et al., 2019; Feurdean et al., 2018; Veldman et al., 2015a, 2015b). Semi-natural grasslands and anthropogenic heathlands are ecosystems where closed canopy forest did not historically develop because of natural processes such as fire or mega fauna, or because of extensive management by local people. Local biodiversity adapted to open spaces has evolved in those ecosystems, and afforestation or tree planting of closed canopy forests is considered as a significant threat for local biodiversity, as highlighted by IPBES (2018a, b). Bubová et al. (2015) reviewed how abandonment of traditional grassland management followed by natural forest succession or active afforestation, is the main driver for the decline of butterfly diversity in Europe.[...] [P]athways in quadrant 2 may provide a significant contribution to climate change that would benefit global ecosystems and biodiversity even if local ecosystems are damaged in the process. However, this is a very uncertain trade-off and would be contrary to the precautionary principle, as explained in section 5.7. In this quadrant, for instance, we can find afforestation of former agricultural land with monoculture plantations: this intervention is likely to lead to carbon benefits in the short-term, but the impacts on local ecosystem should be evaluated carefully, for instance in the framework of landscape mosaic management and climate change resilience. Afforestation of natural grasslands or anthropogenic heathlands could also produce carbon benefits in the medium term, but the cost for local biodiversity, especially for species adapted to open spaces, could be devastating. Indeed, these practices are already discouraged within the Pan-European Guidelines for Afforestation and Reforestation, but they are still popular around the world (Veldman et al., 2015b, 2015a). Further in this quadrant, operations which should be already discouraged by sustainable management guidelines are classified: removing slash in very high quantities could be detrimental for local biodiversity." Camia et al. 2021, pp. 125–147.
^ "The overall carbon impact of afforestation operations needs to be properly calculated including changes in biogenic C-stocks and sinks, the substitution benefits of the newly produced wood, and eventual market-mediated indirect land use change effects. Generally, the overall carbon impact of afforestation is found to be positive, albeit the time scale required might be long (Agostini et al., 2014; Giuntoli et al., 2020b). Nonetheless, not always newly planted forests show a higher C-stock [carbon stock] than existing ecosystems, especially when considering the carbon in soil organic matter. Several studies in our review have tried to provide insights. Bárcena et al. (2014) found increased SOC [soil organic carbon] with afforestation on former cropland and heathland in Northern Europe, however afforestation on former grassland actually decreased SOC levels even for mature forests (>30 years). Laganière et al. (2010) found very similar results from their global meta-analysis, with afforestation on former cropland leading to a significant increase in SOC, but no significant changes in SOC for former pastures and natural grasslands. Furthermore, they also found that the tree species (and thus plantation features) influence the final result, with broadleaves forests generating the highest SOC increase and coniferous forests having the same SOC as the former land use. Li et al. (2012), similarly, found increased SOC for new forests on former cropland and pastureland, but a stable or slightly decreased SOC in former grassland. [...] Pathways in quadrant 3 are probably unlikely to be driven by bioenergy demand, however, they might be definitely valuable for conservation interventions and produce biomass for bioenergy." Camia et al. 2021, pp. 125–147.
^ "Lose-lose pathways include removal of coarse woody debris, removal of low stumps, and conversion of primary or natural forests into plantations. [...] Bubová et al. (2015) reviewed how abandonment of traditional grassland management followed by natural forest succession or active afforestation, is the main driver for the decline of butterfly diversity in Europe. [...] Generally, the overall carbon impact of afforestation is found to be positive, albeit the time scale required might be long (Agostini et al., 2014; Giuntoli et al., 2020b). Nonetheless, not always newly planted forests show a higher C-stock than existing ecosystems, especially when considering the carbon in soil organic matter. Several studies in our review have tried to provide insights. Bárcena et al. (2014) found increased SOC with afforestation on former cropland and heathland in Northern Europe, however afforestation on former grassland actually decreased SOC [soil organic carbon] levels even for mature forests (>30 years). Laganière et al. (2010) found very similar results from their global meta-analysis, with afforestation on former cropland leading to a significant increase in SOC, but no significant changes in SOC for former pastures and natural grasslands. Furthermore, they also found that the tree species (and thus plantation features) influence the final result, with broadleaves forests generating the highest SOC increase and coniferous forests having the same SOC as the former land use. Li et al. (2012), similarly, found increased SOC for new forests on former cropland and pastureland, but a stable or slightly decreased SOC in former grassland. [...] [S]everal pathways are categorized in the lose-lose quadrant and should be discouraged. For instance, the removal of CWD [course woody debris] and low stumps can be detrimental to forest ecosystems while at the same time likely not contributing to reducing carbon emissions in the short or even medium term compared to fossil sources. [...] Further, as expected, the conversion of natural and old growth forests to plantations aiming to provide wood for bioenergy would be extremely negative for local biodiversity, and at the same time it would provide no carbon mitigation in the short-medium term and should be thus discouraged. Similar considerations are valid also for the conversion of naturally regenerating forests to high-intensity management plantations: the impact on local biodiversity is highly negative while, even though wood production might increase, the benefits in terms of carbon mitigation are only accrued in the medium to long term. [...] Depending on local conditions, determining the decay rates on the forest floor, the removal of Coarse Woody Debris and low stumps can be detrimental to forest ecosystems while at the same time likely not contribute to reducing carbon emissions in the short or even medium term compared to fossil sources." Camia et al. 2021, pp. 8–147.
^ "Traditional biomass (fuelwood, charcoal, agricultural residues, animal dung) used for cooking and heating by some 2.8 billion people (38% of global population) in non-OECD countries accounts for more than half of all bioenergy used worldwide (IEA 2017; REN21 2018) (Cross-Chapter Box 7 in Chapter 6). Cooking with traditional biomass has multiple negative impacts on human health, particularly for women, children and youth (Machisa et al. 2013; Sinha and Ray 2015; Price 2017; Mendum and Njenga 2018; Adefuye et al. 2007) and on household productivity, including high workloads for women and youth (Mendum and Njenga 2018; Brunner et al. 2018; Hou et al. 2018; Njenga et al. 2019). Traditional biomass is land-intensive due to reliance on open fires, inefficient stoves and overharvesting of woodfuel, contributing to land degradation, losses in biodiversity and reduced ecosystem services (IEA 2017; Bailis et al. 2015; Masera et al. 2015; Specht et al. 2015; Fritsche et al. 2017; Fuso Nerini et al. 2017). Traditional woodfuels account for 1.9–2.3% of global GHG emissions, particularly in ‘hotspots' of land degradation and fuelwood depletion in eastern Africa and South Asia, such that one-third of traditional woodfuels globally are harvested unsustainably (Bailis et al. 2015). Scenarios to significantly reduce reliance on traditional biomass in developing countries present multiple co-benefits (high evidence, high agreement), including reduced emissions of black carbon, a short-lived climate forcer that also causes respiratory disease (Shindell et al. 2012). A shift from traditional to modern bioenergy, especially in the African context, contributes to improved livelihoods and can reduce land degradation and impacts on ecosystem services (Smeets et al. 2012; Gasparatos et al. 2018; Mudombi et al. 2018)." IPCC 2019a, p. 375.
^ "In the NZE Scenario, bioenergy rapidly shifts to 100% sustainable sources of supply, and sustainable use. There is a complete phase-out of the traditional use of solid biomass for cooking, which is inefficient, often linked to deforestation, and whose pollution was responsible for 2.5 million premature deaths in 2020. The traditional use of solid biomass – estimated at around 40% of total bioenergy supply, or around 25 EJ, today – falls to zero by 2030 in the NZE Scenario, in line with achieving UN Sustainable Development Goal 7 on universal access to affordable, reliable, sustainable and modern energy for all. [...] Sustainable use of bioenergy in the NZE Scenario not only avoids negative impacts such as increased deforestation and competition with food production – it also delivers benefits beyond the energy sector. Shifting from traditional use of biomass to modern bioenergy can avoid undue burdens on women often tasked with collecting wood for fuel, bring health benefits from reduced air pollution and proper waste management, and reduce methane emissions from inefficient combustion and waste decomposition. More generally, sustainable bioenergy can provide a valuable source of employment and income for rural communities in emerging economies." IEA 2021a.

Shortened footnotes

^ EIA 2021a.
^ Darby, Thomas. "What Is Biomass Renewable Energy". Real World Energy. Archived from the original on 2014-06-08. Retrieved 12 June 2014.
^ Correa, Diego F.; Beyer, Hawthorne L.; Fargione, Joseph E.; Hill, Jason D.; et al. (2019). "Towards the implementation of sustainable biofuel production systems". Renewable and Sustainable Energy Reviews. 107: 250–263. doi:10.1016/j.rser.2019.03.005. ISSN 1364-0321. S2CID 117472901. Archived from the original on 17 July 2021. Retrieved 7 February 2021.
^ Daley, Jason (24 April 2018). "The EPA Declared That Burning Wood Is Carbon Neutral. It's Actually a Lot More Complicated". Smithsonian Magazine. Archived from the original on 30 June 2021. Retrieved 2021-09-14.
^ ^a ^b Tester 2012, p. 512.
^ ^a ^b ^c Smil 2017a, p. 162.
^ "Energy Statistics Data Browser – Data Tools". IEA. Retrieved 2022-12-27.
^ ^a ^b IEA 2021a.
^ ^a ^b IPCC 2019b, p. B 7.4.
^ "Bioenergy – Analysis". IEA. Retrieved 2023-01-13.
^ "Bioenergy Basics". Energy.gov. Retrieved 2023-01-13.
^ "Biomass explained - U.S. Energy Information Administration (EIA)". www.eia.gov. Retrieved 2023-01-13.
^ "Renewable Energy Sources and Climate Change Mitigation. Special Report of the Intergovernmental Panel on Climate Change" (PDF). IPCC. Archived (PDF) from the original on 2019-04-12.
^ European Commission. Joint Research Centre. (2021). The use of woody biomass for energy production in the EU. LU: Publications Office. doi:10.2760/831621.
^ ^a ^b ^c IRENA (2014). "Global bioenergy supply and demand projections – a working paper for REmap 2030" International Renewable Energy Agency.
^ Eggers, Jeannette; Melin, Ylva; Lundström, Johanna; Bergström, Dan; Öhman, Karin (2020-05-16). "Management Strategies for Wood Fuel Harvesting—Trade-Offs with Biodiversity and Forest Ecosystem Services". Sustainability. 12 (10): 4089. doi:10.3390/su12104089. ISSN 2071-1050.{{cite journal}}: CS1 maint: unflagged free DOI (link)
^ WBA 2016, p. 4.
^ JRC 2019, p. 3.
^ ^a ^b JRC 2014, p. 75.
^ ^a ^b ^c IEA 2021d.
^ "Household air pollution and health: fact sheet". WHO. 8 May 2018. Retrieved 2020-11-21.
^ "Goal 7: Ensure access to affordable, reliable, sustainable and modern energy for all". SDG Tracker. Archived from the original on 2 February 2021. Retrieved 12 March 2021.
^ ETIP Bioenergy 2022.
^ IRENA 2014, p. 20-21.
^ IEA 2021c.
^ Camia et al. 2021, p. 7.
^ Camia et al. 2018, p. 6.
^ ^a ^b van den Born et al. 2014, p. 20, table 4.2.
^ ETIP Bioenergy 2020.
^ IEA 2019.
^ van den Born et al. 2014, p. 2, 21.
^ ^a ^b ^c ^d EIA 2022.
^ Basu et al. 2013, pp. 171–176.
^ Koukoulas 2016, p. 12.
^ Wild 2015, p. 72.
^ Smil 2015, p. 13.
^ Renewable Energy 2021, pp. 473–483.
^ EIA 2021.
^ Akhtar, Krepl & Ivanova 2018.
^ Liu et al. 2011.
^ "Biochemical Conversion of Biomass". BioEnergy Consult. 2014-05-29. Retrieved 2016-10-18.
^ Correa, Diego F.; Beyer, Hawthorne L.; Fargione, Joseph E.; Hill, Jason D.; et al. (2019). "Towards the implementation of sustainable biofuel production systems". Renewable and Sustainable Energy Reviews. 107: 250–263. doi:10.1016/j.rser.2019.03.005. ISSN 1364-0321. S2CID 117472901. Archived from the original on 17 July 2021. Retrieved 7 February 2021.
^ Daley, Jason (24 April 2018). "The EPA Declared That Burning Wood Is Carbon Neutral. It's Actually a Lot More Complicated". Smithsonian Magazine. Archived from the original on 30 June 2021. Retrieved 14 September 2021.
^ World Health Organization 2016, p. 73.
^ IPCC 2014, p. 616.
^ "Biofuels explained: Ethanol". US Energy Information Administration. 18 June 2020. Archived from the original on 14 May 2021. Retrieved 16 May 2021.
^ Foley, Jonathan (5 March 2013). "It's Time to Rethink America's Corn System". Scientific American. Archived from the original on 3 January 2020. Retrieved 16 May 2021.
^ Ayompe, Lacour M.; Schaafsma, M.; Egoh, Benis N. (1 January 2021). "Towards sustainable palm oil production: The positive and negative impacts on ecosystem services and human wellbeing". Journal of Cleaner Production. 278: 123914. doi:10.1016/j.jclepro.2020.123914. ISSN 0959-6526. S2CID 224853908.
^ Lustgarten, Abrahm (20 November 2018). "Palm Oil Was Supposed to Help Save the Planet. Instead It Unleashed a Catastrophe". The New York Times. ISSN 0362-4331. Archived from the original on 17 May 2019. Retrieved 15 May 2019.
^ Smil 2017a, p. 161.
^ C2ES 2021.
^ JRC 2014, p. 41, table 2.
^ Lamers & Junginger 2013, p. 380.
^ Bird et al. 2010, p. 26.
^ JRC 2014, p. 41.
^ Camia et al. 2018, p. 105.
^ IRENA 2014, pp. 57–58.
^ Zhao, Kaiguang; Jackson, Robert B (2014). "Biophysical forcings of land-use changes from potential forestry activities in North America" (PDF). Ecological Monographs. 84 (2): 329–353. Bibcode:2014EcoM...84..329Z. doi:10.1890/12-1705.1. S2CID 56059160.
^ ^a ^b IEA Bioenergy 2019, p. 3.
^ Camia et al. 2021, pp. 32–33.
^ IPCC 2019a, p. 385.
^ ^a ^b Chatham House 2017, p. 3.
^ Stephenson et al. 2014, pp. 2–3.
^ IPCC 2019a, p. 386.
^ IEA Bioenergy 2019, p. 4–5.
^ Camia et al. 2018, p. 29, 32, 34, 45.
^ IRENA 2019, p. 21.
^ EASAC 2017, p. 23, 26, 35.
^ ^a ^b IPCC 2007, p. 549.
^ IPCC 2019g, p. 194.
^ "Bioenergy – Energy system overview". September 2022.
^ Smil 2015, p. 211, box 7.1.
^ van Zalk & Behrens 2018, pp. 83–91.
^ Camia et al. 2021, p. 146.
^ Gasparatos et al. 2017.
^ Gasparatos et al. 2017, p. 166.
^ Gasparatos et al. 2017, p. 168.
^ Gasparatos et al. 2017, p. 172.
^ Gasparatos et al. 2017, p. 167.
^ IPCC 2019h, p. 628.
^ Springsteen et al. 2011.

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Pokharel, Raju; Grala, Robert K; Latta, Gregory S; Grebner, Donald L; Grado, Stephen C; Poudel, Jagdish (2019-08-30). "Availability of Logging Residues and Likelihood of Their Utilization for Electricity Production in the US South". Journal of Forestry. 117 (6): 543–559. doi:10.1093/jofore/fvz047. ISSN 0022-1201. Retrieved 2022-02-09.
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External links

[IEAdata2020-a-8] In 2020, the world produced a total of 24.6 EJ of electrical energy from all renewables except bioenergy. The individual contributions consists of 15.5 EJ from hydro, 5.8 EJ from wind, 3 EJ from solar and 0.3 EJ from geothermal (all values converted from TWh with IEA's unit converter.)

[IEAdata2020-b-9] In 2020, 9.5 EJ of heat energy for industrial applications was consumed, and 5 EJ of heat for buildings. 3.7 EJ of liquid fuels for transportation was produced (ethanol 2.2 EJ, biodiesel 1.5 EJ), and 2.2 EJ in the form of electricity.

[bioenergy-statistics-2019-3-a-10] "The forestry sector is the largest contributor to the bioenergy mix globally. Forestry products including charcoal, fuelwood, pellets and wood chips account for more than 85% of all the biomass used for energy purposes. One of the primary products from forests that are used for bioenergy production is woodfuel. Most of the woodfuel is used for traditional cooking and heating in developing countries in Asia and Africa. Globally, 1.9 billion m³ of woodfuel was used for energy purposes." WBA 2019, p. 3. In the EU, 60% of all renewable energy comes from biomass. 75% of all biomass is used in the heating and cooling sector. See JRC 2019, p. 1.

[IRENAprojections-b-11] "The International Energy Agency (IEA, 2012) defines traditional use of biomass as: '…the use of wood, charcoal, agricultural residues and animal dung for cooking and heating in the residential sector' and notes that 'it tends to have very low conversion efficiency (10% to 20%) and often relies on unsustainable biomass supply.'" IRENA 2014, p. 7.

[IPCC-2019-637-a-13] "For example, limiting deployment of a mitigation response option will either result in increased climate change or additional mitigation in other sectors. A number of studies have examined limiting bioenergy and BECCS. Some such studies show increased emissions (Reilly et al. 2012). Other studies meet the same climate goal, but reduce emissions elsewhere via reduced energy demand (Grubler et al. 2018; Van Vuuren et al. 2018), increased fossil carbon capture and storage (CCS), nuclear energy, energy efficiency and/or renewable energy (Van Vuuren et al. 2018; Rose et al. 2014; Calvin et al. 2014; Van Vuuren et al. 2017b), dietary change (Van Vuuren et al. 2018), reduced non-CO₂ emissions (Van Vuuren et al. 2018), or lower population (Van Vuuren et al. 2018)." IPCC 2019e, p. 637.

[EIA-2021b-19] "Biofuels are transportation fuels such as ethanol and biodiesel that are made from biomass materials." EIA 2021b.

[EuropeanCommissionGlossary-2018-1-a-20] In EU legislation, biofuel is defined as: "Liquid or gaseous fuel for transport produced from biomass." See European Commission 2018a.

[shortrotationcoppices-30] "Some fast growing tree species can be cut down to a low stump (or stool) when they are dormant in winter and go on to produce many new stems in the following growing season. This practice is well established in the UK and Europe, having been a traditional method of woodland management over several hundred years for a variety of purposes including charcoal, fencing and shipbuilding." Forest Research 2022c.

[shortrotationforests-31] "While short rotation coppicing (SRC) cuts the tree back to a stool to promote the growth of multiple stems, on a regular cycle of roughly 2-4 years, it is also possible to practice something more closely akin to conventional forestry, though on a shorter timescale. Short rotation forestry (SRF) consists of planting a site and then felling the trees when they have reached a size of typically 10-20 cm diameter at breast height. Depending on tree species this usually takes between 8 and 20 years, and is therefore intermediate in timescale between SRC and conventional forestry. This has the effect of retaining the high productivity of a young plantation, but increasing the wood to bark ratio." Forest Research 2022a.

[iea-2021b-212-a-32] "Woody energy crops: Short‐rotation plantings of woody biomass for bioenergy production, such as coppiced willow and miscanthus." IEA 2021b, p. 212.

[IPCC2019cp193-36] "Estimates of marginal/degraded lands currently considered available for bioenergy range from 3.2–14.0 Mkm2, depending on the adopted sustainability criteria, land class definitions, soil conditions, land mapping method and environmental and economic considerations (Campbell et al. 2008; Cai et al. 2011; Lewis and Kelly 2014)." IPCC 2019c, p. 193.

[IRENAprojections-f-37] "Plants convert CO₂ from the atmosphere into biomass. Carbon stored in biomass is called biogenic carbon. Some of this carbon stays above ground and some in the ground. When plants die, decomposition starts. As plant material decays, the stored carbon is released as CO₂ back into the atmosphere." IRENA 2014, p. 45.

[JRC-2014-42-c-39] "Wood from thinnings may, to some extent, be assimilated to harvest residues (especially pre-commercial thinnings). If not collected for bioenergy it would be left in the forest to decay, or combusted at roadside. On the other hand, depending on the wood quality, the use of thinnings wood for bioenergy may compete with other uses, such as pulp and paper or engineered wood. Salvage loggings can also be assimilated to harvest residues. Damaged, dying or dead trees affected by injurious agents, such as wind or ice storms or the spread of invasive epidemic forest pathogens, insects and diseases would remain in the forest and decay or combusted at roadside. Wood removed for prescribed fire hazard control as well can be considered residual wood." JRC 2014, pp. 42–43, table 3.

[pokharel-543-a-40] "This study estimated quantities of logging residues that can physically be recovered from harvest sites and utilized for electricity production in the US South. [...] Although almost all physically available logging residues could be recovered with a relatively short hauling distance, a mail survey indicated that only 4 percent of mills utilized this feedstock." Pokharel et al. 2019, p. 543.

[eggers-2020-2-a-41] "Currently, logging residue extraction, i.e., the harvest of tops and branches left during final felling, occurs on less than 20% of the harvested area in northern Sweden, and about 60% in southern Sweden. Stump harvest occurs to a limited extent today, but is expected to increase to about 5%–10% of the annual clear-felled area in the coming years. Similarly, logging residues constitute the main primary source of woody biofuels in most countries, but in the near future stumps and roundwood may play a more prominent role. Biofuel harvest from early thinnings in dense young forests are currently done to insignificant levels, but will increase, as for stumps, if prize levels rise. Therefore, there is considerable potential for increased extraction rates of primary woody biofuels, especially in northern Sweden, where current extraction rates are relatively low due to longer transport distances and lower harvestable volume per hectare compared to southern Sweden. The situation is similar in other European countries, with large un-used potentials for woody biomass for energy use." Eggers et al. 2020, p. 2.

[dahlberg-2011-a-42] "Logging residues are increasingly being extracted for bioenergy purposes." Dahlberg et al. 2011, p. 1220

[vandenBorn-2014-20-a-43] van den Born et al. distinguish between logging residues in general and dead wood, with the logging residues potential at 14 EJ, and the dead wood potential at 1 EJ annually. For the logging residues potential, see van den Born et al. 2014, p. 20, table 4.2. Regarding the dead wood potential, the authors write: "A biomass pool is dead wood that remains in the forest, either standing or lying, and is transferred to the soil. It is often too costly to harvest dead wood. Besides, it is useful in increasing biodiversity (the proportion of dead wood is a sustainability criteria, (EEA, 2012). The global quantity of dead wood is estimated roughly at 67 Gt of biomass, which is about 11% of the total biomass (FAO, 2010), and about 20 times the annual wood harvest. [...] Dead wood: the global stock of dead wood is estimated at about 1200 EJ of biomass (FAO, 2010). This large pool has built up over a long period of time and in the entire forest area. Assuming an average rotation of 50 to 100 years, this implies a biomass pool of 10 to 20 EJ yr-1 [EJ per year]. When primary forests are excluded because they have not been used (based on FAO, 2010), about 7 to 14 EJ yr-1 of dead biomass remains. Forests with large quantities of dead wood are located in Russia and in parts of Africa. A limitation to the use of salvaged wood is the high costs of access and transport (Niquidet et al., 2012). A conservative estimate of accessible planted forests reduces the pool of available dead wood to about 2 EJ yr-1 biomass (Table 4.2). When an additional assumption is made that half of the dead wood needs to remain in forests to maintain biodiversity (Verkerk et al, 2012), the estimate is about 1 EJ yr-1 biomass available annually for energy production." (p. 15, 19-20)

[Cowie-2021-1215-1216-b-45] "Biomass for bioenergy is usually a by-product of sawlog and pulpwood production for material applications (Dale et al., 2017; Ghaffariyan et al., 2017; Spinelli et al., 2019; Figure 1). Logs that meet quality requirements are used to produce high-value products such as sawnwood and engineered wood products such as cross laminated timber, which can substitute for more carbon-intensive building materials such as concrete, steel and aluminium (Leskinen et al., 2018). Residues from forestry operations (tops, branches, irregular and damaged stem sections, thinnings) and wood processing residues (e.g. sawdust, bark, black liquor) are used for bioenergy (Kittler et al., 2020), including to provide process heat in the forest industry (Hassan et al., 2019). These biomass sources have high likelihood of reducing net GHG emissions when substituting fossil fuels (Hanssen et al., 2017; Matthews et al., 2018), and their use for bioenergy enhances the climate change mitigation value of forests managed for wood production (Cintas, Berndes, Hansson, et al., 2017; Gustavsson et al., 2015, 2021; Schulze et al., 2020; Ximenes et al., 2012). Part of the forest biomass used for bioenergy consists roundwood (also referred to as stemwood), such as small stems from forest thinning. For example, roundwood was estimated to contribute around 20% of the feedstock used for densified wood pellets in the United States in 2018 (US EIA, 2019)." Cowie et al. 2021, pp. 1215–1216.

[internationalforests-47] "The most crucial feedstock for the wood pellet sector is currently sawmill residues (85% of the mix), roundwood (13%), and recovered wood (2%). This mix is likely to change in the coming years with the forecasted expansion of the wood pellet industry. [...] Experience from North America shows that it is possible to use more forest residues as fiber furnish. Although it yields pellets with higher ash content, it is often a lower-cost raw material than, for example, roundwood and wood chips. This practice is increasingly common in both the US South (mainly for pellets exported to Europe) and Canada (mainly exported to Europe and Asia). In Western Canada, the sawmill residue share of the total feedstock has fallen from 97% in 2010 to 72% in 2020, with the balance being forest residues and roundwood." Wood Resources International 2022.

[woodpellets-48] Recalculated from a total production of 43678925 tonnes wood pellets (FAO 2020), with 17 GJ/t energy content.

[woodchips-50] Recalculated from a total production of 265212933 m³ wood chips (FAO 2020), with 3.1 GJ/m³ energy content.

[WBA-2019-3-a-51] "In 2017, 55.6 EJ of biomass was utilized for energy purposes [...]. One of the most promising sectors for growth in bioenergy production is in the form of residues from agriculture sector. Currently, the sector contributes less than 3% to the total bioenergy production." WBA 2019, p. 3.

[vandenBorn-2014-2-21-b-52] The Netherlands Environmental Assessment Agency estimated in 2014 that the total amount of agricultural residues amounts to 78 EJ, with 51 EJ from straw alone (pp. 12-13, table 3.4). "The large production of rice and the relatively low residue flow to the soil makes rice residues the residue with the highest potential for bioenergy, followed by residues from oilcrops, cereals, corn and sugarcane."(p. 19) Because a certain amount should be left in the fields for soil quality purposes, the total amount of agricultural residues that can be sustainably harvested amounts to 24 EJ. van den Born et al. 2014, pp. 2–21.

[bioenergy-statistics-2019-3-b-53] "One of the most promising sectors for growth in bioenergy production is in the form of residues from agriculture sector. Currently, the sector contributes less than 3% to the total bioenergy production. Data shows that utilizing the residues from all major crops for energy can generate approx. 4.3 billion tonnes (low estimate) to 9.4 billion tonnes (high estimate) annually around the world. Utilizing standard energy conversion factors, the theoretical energy potential from residues can be in the range of 17.8 EJ to 82.3 EJ. The major contribution would be from cereals – mainly maize, rice and wheat." WBA 2019, p. 3.

[irena2021-54] "At present, traditional methods of space heating and cooking, such as burning firewood, account for 35 EJ, or two-thirds of total biomass use. By 2030, this would give way to modern biomass consumption, including substantially larger shares for power and transport applications. Power and district heating would reach 36 EJ (one-third of total biomass use in 2030) and transport 31EJ (almost 29%), while heat for industry and buildings would reach up to 41 EJ, of which only 6 EJ would be from less sustainable traditional uses. While global biomass potential is sufficient to meet growing demand, different types of biomass resources are distributed unevenly. Global biomass supply potential in 2030 is estimated to range from 97 EJ to 147 EJ per year. Approximately 40% of this total would originate from agricultural residues and waste (37-66 EJ). The remaining supply potential is shared between energy crops (33-39 EJ) and forest products, including forest residues (24-43 EJ). In geographic terms, the largest supply potential — estimated at 43-77 EJ per year — exists in Asia and Europe. North and South America together account for another 45-55 EJ per year." IRENA 2021.

[Sm2018p547a-62] "Recent studies by Reza et al. and Smith et al. have reported of the fate of inorganics and heteroatoms during HTC [hydrothermal carbonisation] of Miscanthus and indicate significant removal of the alkali metals, potassium and sodium, along with chlorine. [...] Analysis of ash melting behaviour in Smith et al., showed a significant reduction in the slagging propensity of the resulting fuel, along with the fouling and corrosion risk combined. [...] Consequently HTC offers the potential to upgrade Miscanthus from a reasonably low value fuel into a high grade fuel, with a high calorific value, improved handling properties and favourable ash chemistry. [...] HTC at 250 °C can overcome slagging issues and increase the ash deformation temperature from 1040 °C to 1320 °C for early harvested Miscanthus. The chemistry also suggests a reduction in fouling and corrosion propensity for both 250 °C treated fuels." Smith et al. 2018, pp. 547, 556.

[EASAC-2017-2-a-68] "A critical factor in the use of forest biomass in energy provision is the ‘payback time', during which atmospheric concentrations of carbon dioxide (CO₂) will be increased as a result of using biomass. EASAC concludes that the European Commission should consider the extent to which large-scale forest biomass energy use is compatible with UNFCCC targets (of limiting warming to 1.5 °C above pre-industrial levels), and whether a maximum allowable payback period should be set in its sustainability criteria." EASAC 2017, p. 2.

[Ambrose-2021-69] "The UK's plan to burn more trees to generate “renewable” electricity has come under fire from green groups and sustainable investment campaigners over the controversial claim that biomass energy is carbon-neutral. A letter to the government signed by more than a dozen green groups including Greenpeace and Friends of the Earth warns ministers against relying too heavily on plans to capture carbon emissions to help tackle the climate crisis. The plans are being pioneered by Drax Group, which claims that burning wood pellets is carbon-neutral because trees absorb as much carbon dioxide when they grow as they emit when they are burnt. Capturing the carbon emissions from biomass power plants would then effectively create “negative carbon emissions”, according to Drax. The green groups have disputed these claims and warned that the plans “will be costly” and “will not deliver negative emissions” after accounting for the full carbon footprint of biomass in the power sector." Ambrose 2021.

[Grunwald-2021-70] "By definition, clear-cutting trees and combusting their carbon emits greenhouse gases that heat up the earth. But policymakers in the U.S. Congress and governments around the world have declared that no, burning wood for power isn't a climate threat—it's actually a green climate solution. [...] [T]he [...] basic argument is that the carbon released while trees are burning shouldn't count because it's eventually offset by the carbon absorbed while other trees are growing. That is also currently the official position of the U.S. government, along with many other governments around the world. In documentaries, lawsuits and the teenage activist Greta Thunberg's spirited Twitter feed, critics of the industry have suggested an alternative climate strategy: Let trees grow and absorb carbon, then don't burn them. [...] Cutting down a tree and burning it clearly releases more carbon than leaving the tree alone; replanting the tree can only pay back the carbon debt in the long run, and an even longer run if the replanted tree is eventually reharvested. But biomass defenders say that focusing on one tree or even one clear-cut is far too narrow a way to think about forest carbon, because as long as the carbon absorbed by forests equals the carbon released from forests, the climate doesn't care. [...] The industry's position is that wood pellets actually help expand forests, by making it more lucrative for the private landowners who control most U.S. forest land to stay in the forestry business. The opponents argue that what wood pellets make more lucrative is deforestation. [...] “We can't say, ‘Oh, we can sacrifice forest over here, because it's growing over there. We need to stop sacrificing forest.” Grunwald 2021.

[iea-2020-80] The IEA defines carbon neutrality and carbon negativity like so: "Carbon neutrality, or 'net zero,' means that any CO₂ released into the atmosphere from human activity is balanced by an equivalent amount being removed. Becoming carbon negative requires a company, sector or country to remove more CO₂ from the atmosphere than it emits."IEA 2020.

[Camia-2021-83-a-81] EU's Joint Research Centre defines "counterfactual" like so: "The impacts of each bioenergy pathway are evaluated against a counterfactual, i.e. a reference use of the biomass or of the land (thus the results should be interpreted as conditional to the chosen reference)." Camia et al. 2021, p. 83.

[Camia-2018-100-a-82] "It is important to notice that the definition of the reference system (both the energy system and the counterfactual biomass use) is as important as the definition of the bioenergy systems since the stated goal of the study is to assess the mitigation potential of the new systems as compared to the reference one." Camia et al. 2018, p. 100.

[Cowie-2021-1213-1219-1220-a-83] "Critical methodology decisions include the definition of spatial and temporal system boundaries [...] and reference (counterfactual) scenarios [...]. Focus on stack emissions (Option 1) neglects the key differences between fossil and biogenic carbon [...]. Focus on the forest only (Option 2) captures the effects of biomass harvest on forest carbon stocks [...] but omits the climate benefits of displacing fossil fuels. Option 3, the biomass supply chain, overlooks the interactions between biomass and other forest products [...]. Option 4 covers the whole bioeconomy, that is, the forest, the biomass supply chain and all bio-based products from managed forests, and thus provides a more complete assessment of the climate effects of forest bioenergy. In order to quantify the net climate effect of forest bioenergy, assessments should take a whole systems perspective. While this increases the complexity and uncertainty of the assessments, it provides a sound basis for robust decision-making. Biomass for bioenergy should be considered as one component of the bioeconomy (Option 4 [...]). Studies should therefore assess the effects of increasing biomass demand for bioenergy on carbon stocks of the whole forest, and also include the broader indirect impacts on emissions (potentially positive or negative) due to policy- and market-driven influences on land use, use of wood products and GHG-intensive construction materials, and fossil fuel use, outside the bioenergy supply chain. The bioenergy system should be compared with a realistic counterfactual(s) that includes the reference land use and energy systems [...]. This approach is consistent with consequential LCA [...]. The temporal boundary should recognize: forest carbon dynamics, for example, modelling over several rotations; the trajectory for energy system transition; and short- and long-term climate objectives. Matthews et al. (2018) suggest criteria that could be used to identify woody biomass with greater climate benefits when assessed from a full life cycle, whole system perspective." Cowie et al. 2021, pp. 1213, 1219–1220.

[EASAC-2017-23-b-84] A simplified curve, complete with carbon payback and parity times, is available here: EASAC 2017, p. 23.

[JRC-2014-45-a-86] "The GWP is a measure of the effect of the pulse emission of a unit (mass) of a certain gas over its lifetime on the radiative properties of the atmosphere for a certain period of time. In the methodology designed by the IPCC [IPCC 2006], the GWP of CO₂- is taken as the reference value and assigned the value of 1. The reasoning of the authors is that biogenic CO₂- has indeed the same radiative effect of fossil CO₂ on the atmosphere but, while fossil CO₂- can only be reabsorbed by oceans and biosphere (according to the formulation using Bern CC equation, as given by [IPCC 2006]), biogenic-CO₂- has an additional factor which is the reabsorption of the CO₂- via re-growth of vegetation on the same piece of land. By this mathematical formulation, they have been able to assign various values of a so-called GWP_bio- over the typical time horizons of 20, 100 and 500 years and depending on the timing of biomass re-growth. Technically, this factor can then be simply used in a classical LCA and applied as correction factor to the amount of the biogenic-CO₂ emitted by the combustion of biomass." JRC 2014, p. 45.

[EUR-Lex-2018-AnnexVI-b-87] "Annualised emissions from carbon stock changes caused by land-use change, e_l, shall be calculated by dividing total emissions equally over 20 years." European Parliament, Council of the European Union 2018, p. Annex VI.

[EUR-Lex-2018-AnnexVI-c-88] See for instance the European Union's official emission savings percentages for different fuels here: European Parliament, Council of the European Union 2018, p. ANNEX VI. Note that these estimates do not include the average net emissions which results from an eventual land use change prior to planting.

[Camia-2018-89-a-89] "The Renewable Energy Directive (RED), as well as the Fuel Quality Directive (FQD) and the proposal for a RED-Recast (EP 2009, EP 2009b and EC 2016) apply a simplified attributional LCA methodology to assess GHG emissions savings for a series of liquid biofuels pathways used in the transport sector. A similar methodology is also extended to biomass used for power, heat and cooling generation (EC 2016). The RED evaluates the supply-chains GHG emissions of various bioenergy pathways and compares them to each other on a common basis (GHG emission savings with respect to a fossil fuel comparator) to promote the pathways that perform best on this relative scale and to exclude the pathways with the worst technologies and GHG performances." Camia et al. 2018, p. 89.

[Camia-2018-89-91-a-90] "Two main modelling principles are in use in LCA practice: Attributional (A-LCA) and Consequential (C-LCA) modelling, with the former being more widely used for historical and practical reasons. [...] Attributional modelling makes use of historical, fact-based, average, measureable data of known (or at least knowable) uncertainty, and includes all the processes that are identified to relevantly contribute to the system being studied. In attributional modelling, the system is hence modelled “as it is” or “as it was” (or as it is forecasted to be) (EC, 2010). Attributional modelling is also referred to as “accounting”, “book-keeping”, “retrospective”, or “descriptive”. [...] [P]urely attributional LCA studies of bioenergy systems are unable to capture properly all of the complexities linking bioenergy, climate, bioenergy and ecosystem services (e.g. market-mediated effects, biogeophysical, time-dependent effects). [...] The results of these types of assessment are static in time and do not account for biogenic-C flows. It has become established practice in A-LCA to assume that any emission of biogenic CO₂ (release to the atmosphere of the carbon contained in biological resources) is compensated by photosynthesis during the re-growth of the biomass feedstock. This assumption originates from an interpretation of the rules for reporting national GHG inventories to the United Nations Framework Convention on Climate Change (UNFCCC). Biogenic-C flow are accounted for in the land use, land-use change, and forestry (LULUCF) chapter at the time the biomass commodity is harvested and are therefore not accounted for in the energy sector at the time the biomass is burnt (JRC, 2013). It remains valid for system-level analysis, when the changes in biomass carbon stocks are accounted in the land-use sector rather than in the energy sector (EC, 2016c)." Camia et al. 2018, pp. 89–91.

[IPCC2019cp194-91] "Bioenergy from dedicated crops are in some cases held responsible for GHG emissions resulting from indirect land use change (iLUC), that is the bioenergy activity may lead to displacement of agricultural or forest activities into other locations, driven by market-mediated effects. Other mitigation options may also cause iLUC. At a global level of analysis, indirect effects are not relevant because all land-use emissions are direct. iLUC emissions are potentially more significant for crop-based feedstocks such as corn, wheat and soybean, than for advanced biofuels from lignocellulosic materials (Chum et al. 2011; Wicke et al. 2012; Valin et al. 2015; Ahlgren and Di Lucia 2014). Estimates of emissions from iLUC are inherently uncertain, widely debated in the scientific community and are highly dependent on modelling assumptions, such as supply/demand elasticities, productivity estimates, incorporation or exclusion of emission credits for coproducts and scale of biofuel deployment (Rajagopal and Plevin 2013; Finkbeiner 2014; Kim et al. 2014; Zilberman 2017). In some cases, iLUC effects are estimated to result in emission reductions. For example, market-mediated effects of bioenergy in North America showed potential for increased carbon stocks by inducing conversion of pasture or marginal land to forestland (Cintas et al. 2017; Duden et al. 2017; Dale et al. 2017; Baker et al. 2019). There is a wide range of variability in iLUC values for different types of biofuels, from –75–55 gCO₂ MJ–1 (Ahlgren and Di Lucia 2014; Valin et al. 2015; Plevin et al. 2015; Taheripour and Tyner 2013; Bento and Klotz 2014). There is low confidence in attribution of emissions from iLUC to bioenergy." IPCC 2019i, p. 194.

[Bird-2010-5-a-92] One often cited example of indirect land use change is the land use change from forest to agriculture that happened in Brazil after the US started to use some of its harvested corn for ethanol production rather than animal feed. The resulting lower supply of animal feed on the global market was seen as an opportunity by Brazilian farmers, who subsequently cut down forests in order to plant soya beans destined for the animal feed market. See Bird et al. 2010, p. 5, and also Searchinger et al. 2008, pp. 1238–1240 for the original research article.

[Nabuurs-2017-4-a-93] According to Nabuurs et al., displacement factors takes into consideration the difference in CO₂ emissions per unit of primary energy produced, differences in efficiency of energy conversion (e.g. conversion from primary energy to electricity) and in some cases also the emission differences in the supply chains. See Nabuurs, Arets & Schelhaas 2017, p. 4. See also Cowie et al. 2021, p. 1214.

[Cowie-2021-1214-a-94] "Wood and coal have similar CO₂ emission factors, as the ratio of heating values between the two fuels is similar to the ratio of carbon content [...]. Where biomass is co-fired with coal in large power plants, the conversion efficiency may decrease a few percent, although there is usually no significant efficiency penalty when the co-firing ratio is below 10% [...]. Conversion efficiencies depend on fuel properties including moisture content and grindability in addition to heating value [...]. For low rank coal, biomass co-firing (especially torrefied biomass) can increase the boiler efficiency and net power plant efficiency [...]. Smaller biomass-fired plants can have lower electric conversion efficiency than large coal-fired plants, but as they are typically combined heat and power plants, they also displace heat production from other sources, that could otherwise have generated fossil fuel emissions [...]. Large dedicated biomass units (converted from coal) can operate with roughly the same level of thermal efficiency as delivered historically from coal [...]. Cowie et al. 2021, p. 1214.

[IEA-net-zero-2050-d-95] "Bioenergy with carbon capture and storage (BECCS) plays a critical role in the NZE Scenario by offsetting emissions from sectors where full decarbonisation is extremely difficult to achieve. In 2050, around 10% of total bioenergy is used in facilities equipped with carbon capture, utilisation and storage, and around 1.3 billion tonnes of CO₂ is captured using BECCS. Around 45% of this CO₂ is captured in biofuels production, 40% in the electricity sector, and the rest in heavy industry, notably cement production." IEA 2021a.

[JRC-2014-23-51-52-a-96] "In case that there is no raw material displacement from other sectors such as food, feed, fibers or changes in land carbon stocks due to direct or indirect land use change, the assumption of carbon neutrality can still be considered valid for annual crops, agriresidues, short-rotation coppices and energy grasses with short rotation cycles. This can also be valid for analysis with time horizons much longer than the feedstock growth cycles. [...] The timeframe of the comparison too plays a relevant role in the performances of the reference system. If the timeframe chosen is short, the current emissions from the reference system can be considered appropriate and constant. In the case of a long-term analysis, though, also the changes in the fossil reference system have to be accounted for. For instance, practically in all of the studies analyzed the reference system (coal or NG) is kept constant and unchanged for the whole duration of the analysis (even centuries), while, according to EU policies, by 2050 the EU should be decarbonized, implying that future savings might be much smaller than current ones. In this case [...] it may happen that the payback time is never reached. [...] On the other hand, if the reference fossil system gets ‘dirtier', as in the case of most of the unconventional fossil energy (shale gas, bituminous coal etc.) the fossil fuel parity may be reached sooner than with a constant reference fossil fuel." JRC 2014, pp. 23, 51–52. Note that the JRC use the term "payback time" in the sense of "parity time" as defined in Carbon accounting principles above. See JRC 2014, p. 16.

[Cowie-2021-1218-b-97] "Studies of real forest landscapes show that the net GHG effects of bioenergy incentives are more variable than suggested by studies that do not consider economic factors and varying conditions in the forest and wood products sector." Cowie et al. 2021, p. 1218.

[JRC-2014-69-a-98] EU's Joint Research Centre describes how the economic boundaries can expand to reach macro-economic size: "Large scale techno-economic modeling: This type of analysis includes a macroeconomic model that estimates the developments of the wood market in terms of imports, quantity of wood used for wood products and for bioenergy etc. as response to a given decision. The market model is coupled with a forest model that can model changes in carbon stocks in all the pools of forests (including living and dead wood, soil-C etc.) and eventually the carbon stocked in wood products. These two models can then be combined with several scenarios for the substitution of wood products in which a typical LCA (biogenic-CO₂ emissions are set to zero) is applied to calculate the GHG savings due to the use of biomass compared to the alternative materials / feedstocks. The combination of these calculations would provide a clear and quantitative forecast of possible carbon savings or emissions due to different policy scenarios and over different time horizons." JRC 2014, p. 69.

[Camia-2021-86-a-99] See for instance Camia et al. 2021, pp. 86, 100.

[Cowie-2021-1213-1221-a-100] "Wide variation in published estimates of payback time for forest bioenergy systems reflects both inherent differences between these systems and different methodology choices [...]. Critical methodology decisions include the definition of spatial and temporal system boundaries [...] and reference (counterfactual) scenarios [...]. Misleading conclusions on the climate effects of forest bioenergy can be produced by studies that focus on emissions at the point of combustion, or consider only carbon balances of individual forest stands, or emphasize short-term mitigation contributions over long-term benefits, or disregard system-level interactions that influence the climate effects of forest bioenergy." Cowie et al. 2021, pp. 1213, 1221.

[Jonker-2013-371-387-a-102] Jonker et al. examined the carbon intensity for southeastern forests in the US, and concluded that due to the large number of possible methodological choices and reference systems, the calculations produce a wide range of payback and parity times, from below 1 year payback time with landscape level carbon accounting to 27 years with stand level accounting, and parity times of 2 –106 years depending on system boundaries and the choice of alternative scenarios. The authors consider landscape-level carbon accounting more appropriate for the examined situation. Under this precondition, the issue of carbon payback time is basically nonexistent. If comparison against a protection scenario is deemed realistic and policy relevant, and assuming that wood pellets directly replace coal in an average coal power plant, the carbon parity time is 12–46 years; i.e. one or two rotations. Switching to intensively managed plantations yields the most drastic reduction in parity time (below 18 years in 9 of 12 cases). The authors conclude that the choice of carbon accounting method has a significant impact on the carbon payback and parity times. Jonker, Junginger & Faaij 2013, pp. 371–387.

[Madsen-2018-1-a-103] "Studies reporting long carbon debt payback times in general assume that the biomass is utilized for electricity production with low conversion efficiencies and that the woody biomass originates from the dedicated harvest of trees for energy from long rotation forestry. Looking at the current use of bioenergy in the EU, there is little evidence that such supply chains dominate." Madsen & Bentsen 2018, p. 1.

[Cowie-2021-1221-1222-a-104] "Misleading conclusions on the climate effects of forest bioenergy can be produced by studies that focus on emissions at the point of combustion, or consider only carbon balances of individual forest stands, or emphasize short-term mitigation contributions over long-term benefits, or disregard system-level interactions that influence the climate effects of forest bioenergy. Payback time calculations are influenced by subjective methodology choices and do not reflect the contribution of bioenergy within a portfolio of mitigation measures, so it is neither possible nor appropriate to declare a generic value for the maximum acceptable payback time for specific forest bioenergy options. To answer the key question ‘what are the climate implications of policies that promote bioenergy?' assessment should be made at the landscape level, and use a full life cycle approach that includes supply chain emissions, changes in land carbon stocks and other variables influenced by the policies studied. Effects on land cover, land management and the wood products and energy sectors need to be considered, including indirect impacts at international level. The bioenergy system should be compared with reference scenarios (counterfactuals) that describe the most likely alternative land use(s) and energy sources that would be displaced by the bioenergy system, and the probable alternative fates for the biomass being utilized. A no-harvest counterfactual is not realistic in most current circumstances, but markets that pay for carbon sequestration and other ecosystem services could change incentives for harvest in the future."Cowie et al. 2021, pp. 1221–1222.

[Bentsen-2017-1211-a-105] Bentsen examined 245 individual studies and found that the carbon payback time of apparently comparable forest bioenergy supply scenarios vary by up to 200 years, which provides ample room for confusion and dispute about the climate benefits of forest bioenergy. He concludes that the outcome of carbon debt studies lie in the assumptions, and that methodological rather than ecosystem and management related assumptions determine the findings. The findings are therefore seen as inadequate for informing and guiding policy development. Bentsen 2017, p. 1211.

[JRC-2014-75-a-106] "There is a large variability in the literature results for fossil fuel parity times. This is due to differences in the characteristics of the forest system considered (growth rate, management), in the carbon pools included, in the system boundaries definition and in the reference baseline used in the analysis." JRC 2014, p. 75.

[Camia-2021-93-a-107] EU's Joint Research Centre recommend that "[...] policymakers and scientists alike recognize that diverging values, worldviews, and ethical perceptions of natural resources and their management are a core part of the debate. These will not be solved by more scientific research, because science is a social endeavour where value-choices and judgements are inevitable. Transparency is key and cooperation with policymakers and co-creation of useful results should be welcomed." Camia et al. 2021, p. 93. In a presentation of this report for IEA Bioenergy, the JRC staff expand on this conclusion. They write that the question “Does forest bioenergy mitigate climate change?” really has no answer, as it is depends on "modelling approaches and the assumptions about hypothetical futures", and that researchers "come to equally valid, but opposite answers depending on assumptions chosen." They also write that "the assumptions chosen will align (consciously or unconsciously) with the worldviews and ethical values of the authors." According to the JRC, supporters of bioenergy usually have a more anthropocentric view of the human-nature relationship, while opposers of bioenergy are more aligned with nature conservation values. These norms lead to different concerns and definitions of what sustainability really is. See Mubareka, Giuntoli & Grassi 2021, pp. 8–9.

[jrc-2014-75-b-108] "Most of the forest feedstocks used for bioenergy, as of today, are industrial residues, waste wood, residual wood (thinnings, harvest residues, salvage loggings, landscape care wood etc.) for which, in the short to medium term, GHG savings may be achieved. On the other hand, in the case of stemwood harvested for bioenergy purposes only, if all the carbon pools and their development with time are considered in both the bioenergy and the reference fossil scenario, there is an actual increase in CO₂ emissions compared to fossil fuels in the short-term (few decades). In the longer term (centuries) also stemwood may reach the fossil fuel parity points and then generate GHG savings if the productivity of the forest is not reduced because of bioenergy production. [...] The results attained are strongly correlated with the following parameters: the fossil fuel replaced, efficiency of the biomass utilization, the future growth rate of the forest, the frequency and intensity of biomass harvests and the initial landscape carbon stock." JRC 2014, p. 75.

[Camia-2021-143-a-111] "Increased removal of FWD [fine woody debris], low stumps, CWD (course woody debris): It depends strongly on the decay rates considered. For instance, (Giuntoli et al., 2015) and (Giuntoli et al., 2016) found that residues with decay rates of 11.5%/year would mitigate climate change compared to natural gas heating and natural gas electricity after about 20 years, but residues with decay rate lower than 2.7%/year would take more than 86 years to payback compared to natural gas heating, or more than a century compared to the current EU power mix. FWD are thus likely to achieve carbon mitigation in a short term. However, decay rates for low stumps have been reported to range between 0.7%/year up to even 11%/year (Persson and Egnell, 2018), depending on climatic conditions and species. Considering a representative decay rate for temperate/boreal forests of between 3 and 6%/year would mean stumps would be unlikely to achieve climate mitigation before 50 years. This is substantiated also by the work of (Laganière et al., 2017). However, we indicate a range of uncertainty across other climate change levels. CWD are very likely to exhibit low decay rates and to have very long payback times." Camia et al. 2021, p. 143. See also JRC 2014, pp. 16–17, 43–44.

[Lamers-2013-379-a-112] Lamers & Junginger examined a number of studies and argue that parity times for residues "[...] mostly vary depending on the respective fossil fuel used in the reference scenario [...]." However, the second most important influencing factor "[...] is the size/diameter of the residue and the forest biome, i.e. conditions affecting the decay rate." The shortest parity times were found for forest residues which would otherwise be burned at the factory or roadside. This immediate carbon release in the alternative scenario causes an immediate carbon benefit and a net zero parity time for the bioenergy scenario. The longest parity times were for stump harvest in the cold boreal forests of northern Finland, when compared to a natural decay scenario for the stumps, and instead production of electricity from natural gas. For stemwood, parity times vary to some degree by forest biome with significantly shorter periods for highly productive regions, such as the temperate moist forests of the South-Eastern USA. In the boreal or sub-boreal forests, parity times against a forest protection scenario are about twice as large, but there are variations between studies. Under specific conditions, for instance where insect infestation has killed a large amount of merchantable timber stock, "[...] bioenergy harvest can reach parity times as low a zero." The high share of fast decaying tree biomass in the protection scenario shortens parity times. Parity times against regular timber harvest (business as usual) vary greatly with the fossil fuel alternative scenario, the shortest being coal and oil compared to natural gas. Afforestation on the other hand has a parity time of zero years if the land area in question would not be sequestering large amounts of carbon otherwise. Lamers & Junginger 2013, p. 379.

[JRC-2014-17-a-113] "There is a large variability in the results of forest bioenergy fossil fuel parity times calculations. This large variability depends on the many different characteristics of the systems compared and non-consistent modeling assumptions and approaches. The first, most important assumption is on the fossil fuel displaced. Then, concerning both the bioenergy system and the reference fossil system the following characteristics heavily impact the results: efficiency in the final use, future growth rate of the forest, the frequency and intensity of biomass harvests, the initial forest carbon stock, the forest management practices assumed." JRC 2014, p. 17.

[JRC-2014-34-a-115] "The reviewed studies show payback times ranging from 0 to almost 500 years. This large variability depends on the many different characteristics and assumptions on both the forest/bioenergy system and the reference fossil system. The most straight forward relation is with the fossil fuel used as a reference in the fossil scenario. Obviously, the more carbon intensive the fossil fuel replaced is, the shorter is the payback time. [...] A further correlation exists with the efficiency of the biomass utilization. The less efficient the bioenergy system is, the longer are the payback times. In case of electricity production, in biomass only plants, the electrical efficiency of biomass conversion is lower than the fossil, while thermal conversion energetic efficiency is similar for biomass and fossil fuels. In co-firing plants, biomass generally achieves the same efficiency as coal. An intensive processing, such as for liquid biofuel substitution via lignocellulosic ethanol, causes much longer payback times because of the loss of energy in the biofuels production (about half of the energy content of the biomass is lost in the processing [...]. The slower the forest growth rate is, the longer is the payback time. The forest growth rate depends on the latitude (boreal, temperate, tropical), but also on specific characteristics of the trees species, the microclimate and the soil fertility." JRC 2014, p. 34. Note that the JRC use the term "payback time" in the sense of "parity time" as defined in Carbon accounting principles above. See JRC 2014, p. 16.

[hanssen-2017-3-a-116] See Hanssen et al. 2017: Figure S3 at page 3 in the Supporting Information document, link to document available at the bottom of the article.)

[IRENAprojections-i-119] "In addition to the EU, the US has also amended its Renewables Fuel Standard 1 (RFS1) to include minimum life-cycle GHG emissions in the RFS2. RFS2 distinguishes between the production of conventional and advanced biofuels, which are defined based on their GHG abatement potential. All biofuels which can save up to 20% GHG in their life cycle compared to the petroleumbased equivalents are categorised as conventional. Conventional biofuel production is limited to 15 billion gallons to 2022. Advanced biofuels production accounts for the remainder 21 billion gallons. A biofuel can be considered advanced if it saves at least 50% GHG. Cellulosic biofuels require a 60% GHG emission reduction compared to the petrochemical equivalent (EPA, 2012). These emissions include ILUC GHG emissions." IRENA 2014, p. 47.

[Eur-Lex-2018-AnnexVI-a-120] The estimates are for the "medium case" considered (case 2a); a pellet mill that uses wood for processing heat, but sources electricity from the grid. Estimates (for forest residue based pellets) reduce to 50–58% when fossil fuels is used for processing heat (case 1), but increase to 84-92% when electricity is sourced from a CHP biomass power plant (case 3a). See European Parliament, Council of the European Union 2018, p. Annex VI.

[Mc2017p493b-121] "Any soil disturbance, such as ploughing and cultivation, is likely to result in short-term respiration losses of soil organic carbon, decomposed by stimulated soil microbe populations (Cheng, 2009; Kuzyakov, 2010). Annual disturbance under arable cropping repeats this year after year resulting in reduced SOC levels. Perennial agricultural systems, such as grassland, have time to replace their infrequent disturbance losses which can result in higher steady-state soil carbon contents (Gelfand et al., 2011; Zenone et al., 2013)." McCalmont et al. 2017, p. 493.

[IPCC2019a-122] "Tillage breaks apart soil aggregates which, among other functions, are thought to inhibit soil bacteria, fungi and other microbes from consuming and decomposing SOM (Grandy and Neff 2008). Aggregates reduce microbial access to organic matter by restricting physical access to mineral-stabilised organic compounds as well as reducing oxygen availability (Cotrufo et al. 2015; Lehmann and Kleber 2015). When soil aggregates are broken open with tillage in the conversion of native ecosystems to agriculture, microbial consumption of SOC and subsequent respiration of CO₂ increase dramatically, reducing soil carbon stocks (Grandy and Robertson 2006; Grandy and Neff 2008)." IPCC 2019a, p. 393.

[Wh2018p150a-123] "In 2015, a workshop was convened with researchers, policymakers and industry/business representatives from the UK, EU and internationally. Outcomes from global research on bioenergy land‐use change were compared to identify areas of consensus, key uncertainties, and research priorities. [...] Our analysis suggests that the direct impacts of dedicated perennial bioenergy crops on soil carbon and nitrous oxide are increasingly well understood and are often consistent with significant life cycle GHG mitigation from bioenergy relative to conventional energy sources. We conclude that the GHG balance of perennial bioenergy crop cultivation will often be favourable, with maximum GHG savings achieved where crops are grown on soils with low carbon stocks and conservative nutrient application, accruing additional environmental benefits such as improved water quality. The analysis reported here demonstrates there is a mature and increasingly comprehensive evidence base on the environmental benefits and risks of bioenergy cultivation which can support the development of a sustainable bioenergy industry." Whitaker et al. 2018, p. 150.

[Hektor-2016-4-b-125] Hektor et al. argue that flue gas condensation devices combined with natural drying of biomass makes it possible to achieve similar or better combustion efficiency than coal: "When burning moist biomass, energy is 'lost' in the evaporation of water. However, modern technology makes it possible to recover a large portion of that energy by flue gas condensation devices." The author also recommends "[...] simpler measures, such as natural drying [...]", and argue that "[...] state-of-the art technologies are nowadays generally included in new applications of biomass energy [...]" and that "[...] taking these factors into consideration, biomass would have about the same gross CO₂ emissions per generated amount of energy as coal [...]." Hektor, Backéus & Andersson 2016, p. 4. See also OECD/IEA 2004, p. 20.

[IPCC-2006-2.16-2.17-a-127] The individual emission rates are: Wood 112 000 kg CO₂eq per TJ, anthracite 98 300, coking coal 94 600, other bituminous 94 600, sub-bituminous 96 100, lignite 101 000. IPCC 2006a, pp. 2.16–2.17.

[ipcc-2019-a-368-a-128] "Estimating gross emissions only, creates a distorted representation of human impacts on the land sector carbon cycle. While forest harvest for timber and fuelwood and land-use change (deforestation) contribute to gross emissions, to quantify impacts on the atmosphere, it is necessary to estimate net emissions, that is, the balance of gross emissions and gross removals of carbon from the atmosphere through forest regrowth [...]." IPCC 2019a, p. 368.

[ieabioenergy-2019-3-4-a-129] "It is incorrect to determine the climate change effect of using biomass for energy by comparing GHG emissions at the point of combustion [...] the misplaced focus on emissions at the point of combustion blurs the distinction between fossil and biogenic carbon, and it prevents proper evaluation of how displacement of fossil fuels with biomass affects the development of atmospheric GHG concentrations." IEA Bioenergy 2019, pp. 3–4.

[IPCC-2019-367-a-131] "The trends of productivity shown by several remote-sensing studies (see previous section) are largely consistent with mapping of forest cover and change using a 34-year time series of coarse resolution satellite data (NOAA AVHRR) (Song et al. 2018). This study, based on a thematic classification of satellite data, suggests that (i) global tree canopy cover increased by 2.24 million km² between 1982 and 2016 (corresponding to +7.1%) but with regional differences that contribute a net loss in the tropics and a net gain at higher latitudes, and (ii) the fraction of bare ground decreased by 1.16 million km² (corresponding to –3.1%), mainly in agricultural regions of Asia (Song et al. 2018), see Figure 4.5. Other tree or land cover datasets show opposite global net trends (Li et al. 2018b), but high agreement in terms of net losses in the tropics and large net gains in the temperate and boreal zones (Li et al. 2018b; Song et al. 2018; Hansen et al. 2013)." IPCC 2019a, p. 367.

[Stephenson-2014-3-a-135] "Second, our findings are similarly compatible with the well-known age-related decline in productivity at the scale of even-aged forest stands. [...] We highlight the fact that increasing individual tree growth rate does not automatically result in increasing stand productivity because tree mortality can drive orders-of-magnitude reductions in population density. That is, even though the large trees in older, even-aged stands may be growing more rapidly, such stands have fewer trees. Tree population dynamics, especially mortality, can thus be a significant contributor to declining productivity at the scale of the forest stand." Stephenson et al. 2014, p. 3.

[ipcc-2019-a-351-a-137] "SFM [sustainable forest management] applied at the landscape scale to existing unmanaged forests can first reduce average forest carbon stocks and subsequently increase the rate at which CO₂ is removed from the atmosphere, because net ecosystem production of forest stands is highest in intermediate stand ages (Kurz et al. 2013; Volkova et al. 2018; Tang et al. 2014). The net impact on the atmosphere depends on the magnitude of the reduction in carbon stocks, the fate of the harvested biomass (i.e. use in short – or long-lived products and for bioenergy, and therefore displacement of emissions associated with GHG-intensive building materials and fossil fuels), and the rate of regrowth. Thus, the impacts of SFM on one indicator (e.g., past reduction in carbon stocks in the forested landscape) can be negative, while those on another indicator (e.g., current forest productivity and rate of CO₂ removal from the atmosphere, avoided fossil fuel emissions) can be positive. Sustainably managed forest landscapes can have a lower biomass carbon density than unmanaged forest, but the younger forests can have a higher growth rate, and therefore contribute stronger carbon sinks than older forests (Trofymow et al. 2008; Volkova et al. 2018; Poorter et al. 2016)." IPCC 2019a, p. 351.

[IEA-net-zero-2050-c-138] "Bioenergy provides only 5% of total electricity generation in 2050, but it is an important source of low-emissions flexibility to complement variable generation from solar PV and wind. In the industry sector, where solid bioenergy demand reaches 20 EJ in 2050, it is used to meet high temperature heat needs that cannot be easily electrified such as paper and cement production. In 2050, bioenergy meets 60% of energy demand in the paper sector and 30% of energy demand for cement production." IEA 2021a.

[IEA-net-zero-by-2050-0-94-139] The IEA estimates that replacing short rotation coppice forests with hydrogen production (for heat processing purposes) would cost 4.5 trillion USD: "The additional wind, solar, battery and electrolyser capacity, together with the electricity networks and storage needed to support this higher level of deployment would cost more than USD 5 trillion by 2050. This is USD 4.5 trillion more than would be needed if the use of bioenergy were to be expanded as envisaged in the NZE [Net Zero Emissions scenario], and would increase the total investment needed in the NZE by 3%. While it might therefore be possible still to achieve net‐zero emissions in 2050 without expanding land use for bioenergy, this would make the energy transition significantly more expensive. " IEA 2021b, p. 94.

[EASAC-2017-34-a-143] "The potentially very long payback periods for forest biomass raise important issues given the UNFCCC's aspiration of limiting warming to 1.5 °C above preindustrial levels to ‘significantly reduce the risks and impacts of climate change'. On current trends, this may be exceeded in around a decade. Relying on forest biomass for the EU's renewable energy, with its associated initial increase in atmospheric carbon dioxide levels, increases the risk of overshooting the 1.5°C target if payback periods are longer than this. The European Commission should consider the extent to which large-scale forest biomass energy use is compatible with UNFCCC targets and whether a maximum allowable payback period should be set in its sustainability criteria." EASAC 2017, p. 34.

[ipcc-2019j-2.67-a-146] The forest landscape works as a proxy for calculating specifically human GHG emissions: "In the AFOLU [Agriculture, Forestry and Other Land Use] sector, the management of land is used as the best approximation of human influence and thus, estimates of emissions and removals on managed land are used as a proxy for anthropogenic emissions and removals on the basis that the preponderance of anthropogenic effects occurs on managed lands (see Vol. 4 Chapter 1). This allows for consistency, comparability, and transparency in estimation. Referred to as the Managed Land Proxy (MLP), this approach is currently recognised by the IPCC as the only universally applicable approach to estimating anthropogenic emissions and removals in the AFOLU sector (IPCC 2006, IPCC 2010)." IPCC 2019j, p. 2.67.

[IPCC-2019-2.72-a-147] "The natural disturbance component is subtracted from the total estimate of [...] emissions and removals, yielding an estimate of the emissions and removals associated with human activity on managed land." See IPCC 2019j, p. 2.72. "The 2006 IPCC Guidelines are designed to assist in estimating and reporting national inventories of anthropogenic greenhouse gas emissions and removals. For the AFOLU Sector, anthropogenic greenhouse gas emissions and removals by sinks are defined as all those occurring on ‘managed land'. Managed land is land where human interventions and practices have been applied to perform production, ecological or social functions. [...] This approach, i.e., the use of managed land as a proxy for anthropogenic effects, was adopted in the GPG–LULUCF and that use is maintained in the present guidelines. The key rationale for this approach is that the preponderance of anthropogenic effects occurs on managed lands. By definition, all direct human-induced effects on greenhouse gas emissions and removals occur on managed lands only. While it is recognized that no area of the Earth's surface is entirely free of human influence (e.g., CO₂ fertilization), many indirect human influences on greenhouse gases (e.g., increased N deposition, accidental fire) will be manifested predominately on managed lands, where human activities are concentrated. Finally, while local and short-term variability in emissions and removals due to natural causes can be substantial (e.g., emissions from fire, see footnote 1), the natural ‘background' of greenhouse gas emissions and removals by sinks tends to average out over time and space. This leaves the greenhouse gas emissions and removals from managed lands as the dominant result of human activity. Guidance and methods for estimating greenhouse gas emissions and removals for the AFOLU Sector now include: • CO₂ emissions and removals resulting from C stock changes in biomass, dead organic matter and mineral soils, for all managed lands; • CO₂ and non-CO₂ emissions from fire on all managed land; • N₂O emissions from all managed soils; • CO₂ emissions associated with liming and urea application to managed soils; • CH4 emissions from rice cultivation; • CO₂ and N₂O emissions from cultivated organic soils; • CO₂ and N₂O emissions from managed wetlands (with a basis for methodological development for CH4 emissions from flooded land in an Appendix 3); • CH4 emission from livestock (enteric fermentation); • CH4 and N₂O emissions from manure management systems; and • C stock change associated with harvested wood products." See IPCC 2006b, p. 1.5.

[IPCC-2019-638-a-149] "Limitations on bioenergy and BECCS can result in increases in the cost of mitigation (Kriegler et al. 2014; Edmonds et al. 2013). Studies have also examined limiting CDR, including reforestation, afforestation, and bioenergy and BECCS (Kriegler et al. 2018a,b). These studies find that limiting CDR can increase mitigation costs, increase food prices, and even preclude limiting warming to less than 1.5°C above pre-industrial levels (Kriegler et al. 2018a,b; Muratori et al. 2016)." IPCC 2019e, p. 638.

[iea-bioenergy-2019-4-a-150] "Concern about near-term emissions is not a strong argument for stopping investments that contribute to net emissions reduction beyond 2030, be it the scaling-up of battery manufacturing to support electrification of car fleets, the development of rail infrastructure, or the development of biomass supply systems and innovation to provide biobased products displacing fossil fuels, cement and other GHG-intensive products. We assert that it is critical to focus on the global emissions trajectory required to achieve climate stabilization, acknowledging possible trade-offs between short- and long-term emissions reduction objectives. A strong focus on short-term carbon balances may result in decisions that make long-term climate objectives more difficult to meet."IEA Bioenergy 2019, p. 4.

[Camia-2021-107-a-154] "Pathways in the first and fourth quadrants are relatively clear situations in which trade-offs are not evident, and should thus clearly be a target for governance measures; in the sense that pathways in quadrant 1 should be incentivised, while pathways in quadrant 4 should be discouraged. Forest bioenergy pathways which fit within the first quadrant are the ones that are very likely to contribute to climate change mitigation in a short-medium term, and at the same time are likely to improve the condition of local ecosystems and biodiversity (or at least do not affect paths of ecosystem restoration). Pathways in the fourth quadrant are the ones that are unlikely to contribute to climate change mitigation in the short-medium term and at the same time are likely to further degrade ecosystems' condition. Conversely, pathways in quadrants 2 and 3 are the ones for which trade-offs between climate mitigation and biodiversity can be identified or assumed. Pathways in quadrant 2 are the ones that even though they are likely to mitigate climate change, they are also likely to negatively impact local biodiversity. For these pathways, safeguards or mitigation strategies should be investigated, and if available, should be considered mandated as contingent to the promotion of bioenergy. This case is also the only case in which the trade-off mentioned above (global climate change mitigation vs. local degradation) could influence the final evaluation of the pathway. Pathways in the third quadrant are likely to improve local ecosystem condition, but might not mitigate climate change in the short term. In these cases, bioenergy production might be seen as a by-product of restoration operations. In both cases in quadrants 2 & 3, trade-offs that cannot be resolved will need to be weighted and discussed during the decision-making process." Camia et al. 2021, p. 107.

[Camia-2021-8-149-a-158] "Win-win management practices that benefit climate change mitigation and have either a neutral or positive effect on biodiversity include removal of slash (fine, woody debris) below thresholds defined according to local conditions, and afforestation of former arable land with mixed forest or naturally regenerating forests. [...] [C]oppice forests are particularly important in Mediterranean countries, they provide many ecosystem services, have relevant socio-economic functions in many rural areas and are mainly utilised for bioenergy. However, in large areas coppices are no longer managed or completely abandoned, resulting in old or overgrown declining stands. In these cases, it is suggested to encourage active forest management, that would enhance the capacity of these ecosystems to store carbon and supply services. Depending on local considerations the preferred option could be active conversion to high forest, or coppice restoration (see Section 5.9.2). [...] [W]e find that collecting slash within the limits of locally recommended thresholds could generate energy without damaging forest ecosystems and at the same time likely contributing to reducing GHG emissions. Similarly, afforesting former agricultural land with mixed species plantations or with naturally regenerating forests would enhance the terrestrial sink even before producing biomass for energy and thus would contribute to climate change mitigation, while at the same time improving ecosystems' conditions. [...] Collecting slash within the limits of locally recommended thresholds could be used to generate energy without damaging forest ecosystems while likely contributing to reducing GHG emissions. Afforesting former agricultural land with mixed species plantations or with naturally regenerating forests would enhance the terrestrial sink even before producing biomass for material and energy uses and thus would contribute to climate change mitigation, while at the same time improving ecosystems' conditions. [...] [C]ollection and use of low stumps within locally established thresholds in climate areas with high decay rates could potentially provide carbon emissions mitigation without damaging local biodiversity; local conditions should be evaluated in these cases." Camia et al. 2021, pp. 8–149.

[Camia-2021-125-147-a-160] "Although not extensively captured in the case studies, there is clear consensus in the literature that afforestation of primary, ancient grassland ecosystems which were never forests, may have very detrimental effects on local biodiversity; some authors compare these effects to the destructive effects of deforestation (Abreu et al., 2017; Bond, 2016; Bond et al., 2019; Feurdean et al., 2018; Veldman et al., 2015a, 2015b). Semi-natural grasslands and anthropogenic heathlands are ecosystems where closed canopy forest did not historically develop because of natural processes such as fire or mega fauna, or because of extensive management by local people. Local biodiversity adapted to open spaces has evolved in those ecosystems, and afforestation or tree planting of closed canopy forests is considered as a significant threat for local biodiversity, as highlighted by IPBES (2018a, b). Bubová et al. (2015) reviewed how abandonment of traditional grassland management followed by natural forest succession or active afforestation, is the main driver for the decline of butterfly diversity in Europe.[...] [P]athways in quadrant 2 may provide a significant contribution to climate change that would benefit global ecosystems and biodiversity even if local ecosystems are damaged in the process. However, this is a very uncertain trade-off and would be contrary to the precautionary principle, as explained in section 5.7. In this quadrant, for instance, we can find afforestation of former agricultural land with monoculture plantations: this intervention is likely to lead to carbon benefits in the short-term, but the impacts on local ecosystem should be evaluated carefully, for instance in the framework of landscape mosaic management and climate change resilience. Afforestation of natural grasslands or anthropogenic heathlands could also produce carbon benefits in the medium term, but the cost for local biodiversity, especially for species adapted to open spaces, could be devastating. Indeed, these practices are already discouraged within the Pan-European Guidelines for Afforestation and Reforestation, but they are still popular around the world (Veldman et al., 2015b, 2015a). Further in this quadrant, operations which should be already discouraged by sustainable management guidelines are classified: removing slash in very high quantities could be detrimental for local biodiversity." Camia et al. 2021, pp. 125–147.

[Camia-2021-125-147-b-161] "The overall carbon impact of afforestation operations needs to be properly calculated including changes in biogenic C-stocks and sinks, the substitution benefits of the newly produced wood, and eventual market-mediated indirect land use change effects. Generally, the overall carbon impact of afforestation is found to be positive, albeit the time scale required might be long (Agostini et al., 2014; Giuntoli et al., 2020b). Nonetheless, not always newly planted forests show a higher C-stock [carbon stock] than existing ecosystems, especially when considering the carbon in soil organic matter. Several studies in our review have tried to provide insights. Bárcena et al. (2014) found increased SOC [soil organic carbon] with afforestation on former cropland and heathland in Northern Europe, however afforestation on former grassland actually decreased SOC levels even for mature forests (>30 years). Laganière et al. (2010) found very similar results from their global meta-analysis, with afforestation on former cropland leading to a significant increase in SOC, but no significant changes in SOC for former pastures and natural grasslands. Furthermore, they also found that the tree species (and thus plantation features) influence the final result, with broadleaves forests generating the highest SOC increase and coniferous forests having the same SOC as the former land use. Li et al. (2012), similarly, found increased SOC for new forests on former cropland and pastureland, but a stable or slightly decreased SOC in former grassland. [...] Pathways in quadrant 3 are probably unlikely to be driven by bioenergy demand, however, they might be definitely valuable for conservation interventions and produce biomass for bioenergy." Camia et al. 2021, pp. 125–147.

[Camia-2021-8-147-a-162] "Lose-lose pathways include removal of coarse woody debris, removal of low stumps, and conversion of primary or natural forests into plantations. [...] Bubová et al. (2015) reviewed how abandonment of traditional grassland management followed by natural forest succession or active afforestation, is the main driver for the decline of butterfly diversity in Europe. [...] Generally, the overall carbon impact of afforestation is found to be positive, albeit the time scale required might be long (Agostini et al., 2014; Giuntoli et al., 2020b). Nonetheless, not always newly planted forests show a higher C-stock than existing ecosystems, especially when considering the carbon in soil organic matter. Several studies in our review have tried to provide insights. Bárcena et al. (2014) found increased SOC with afforestation on former cropland and heathland in Northern Europe, however afforestation on former grassland actually decreased SOC [soil organic carbon] levels even for mature forests (>30 years). Laganière et al. (2010) found very similar results from their global meta-analysis, with afforestation on former cropland leading to a significant increase in SOC, but no significant changes in SOC for former pastures and natural grasslands. Furthermore, they also found that the tree species (and thus plantation features) influence the final result, with broadleaves forests generating the highest SOC increase and coniferous forests having the same SOC as the former land use. Li et al. (2012), similarly, found increased SOC for new forests on former cropland and pastureland, but a stable or slightly decreased SOC in former grassland. [...] [S]everal pathways are categorized in the lose-lose quadrant and should be discouraged. For instance, the removal of CWD [course woody debris] and low stumps can be detrimental to forest ecosystems while at the same time likely not contributing to reducing carbon emissions in the short or even medium term compared to fossil sources. [...] Further, as expected, the conversion of natural and old growth forests to plantations aiming to provide wood for bioenergy would be extremely negative for local biodiversity, and at the same time it would provide no carbon mitigation in the short-medium term and should be thus discouraged. Similar considerations are valid also for the conversion of naturally regenerating forests to high-intensity management plantations: the impact on local biodiversity is highly negative while, even though wood production might increase, the benefits in terms of carbon mitigation are only accrued in the medium to long term. [...] Depending on local conditions, determining the decay rates on the forest floor, the removal of Coarse Woody Debris and low stumps can be detrimental to forest ecosystems while at the same time likely not contribute to reducing carbon emissions in the short or even medium term compared to fossil sources." Camia et al. 2021, pp. 8–147.

[IPCC2019ap375-165] "Traditional biomass (fuelwood, charcoal, agricultural residues, animal dung) used for cooking and heating by some 2.8 billion people (38% of global population) in non-OECD countries accounts for more than half of all bioenergy used worldwide (IEA 2017; REN21 2018) (Cross-Chapter Box 7 in Chapter 6). Cooking with traditional biomass has multiple negative impacts on human health, particularly for women, children and youth (Machisa et al. 2013; Sinha and Ray 2015; Price 2017; Mendum and Njenga 2018; Adefuye et al. 2007) and on household productivity, including high workloads for women and youth (Mendum and Njenga 2018; Brunner et al. 2018; Hou et al. 2018; Njenga et al. 2019). Traditional biomass is land-intensive due to reliance on open fires, inefficient stoves and overharvesting of woodfuel, contributing to land degradation, losses in biodiversity and reduced ecosystem services (IEA 2017; Bailis et al. 2015; Masera et al. 2015; Specht et al. 2015; Fritsche et al. 2017; Fuso Nerini et al. 2017). Traditional woodfuels account for 1.9–2.3% of global GHG emissions, particularly in ‘hotspots' of land degradation and fuelwood depletion in eastern Africa and South Asia, such that one-third of traditional woodfuels globally are harvested unsustainably (Bailis et al. 2015). Scenarios to significantly reduce reliance on traditional biomass in developing countries present multiple co-benefits (high evidence, high agreement), including reduced emissions of black carbon, a short-lived climate forcer that also causes respiratory disease (Shindell et al. 2012). A shift from traditional to modern bioenergy, especially in the African context, contributes to improved livelihoods and can reduce land degradation and impacts on ecosystem services (Smeets et al. 2012; Gasparatos et al. 2018; Mudombi et al. 2018)." IPCC 2019a, p. 375.

[IEA-net-zero-2050-167] "In the NZE Scenario, bioenergy rapidly shifts to 100% sustainable sources of supply, and sustainable use. There is a complete phase-out of the traditional use of solid biomass for cooking, which is inefficient, often linked to deforestation, and whose pollution was responsible for 2.5 million premature deaths in 2020. The traditional use of solid biomass – estimated at around 40% of total bioenergy supply, or around 25 EJ, today – falls to zero by 2030 in the NZE Scenario, in line with achieving UN Sustainable Development Goal 7 on universal access to affordable, reliable, sustainable and modern energy for all. [...] Sustainable use of bioenergy in the NZE Scenario not only avoids negative impacts such as increased deforestation and competition with food production – it also delivers benefits beyond the energy sector. Shifting from traditional use of biomass to modern bioenergy can avoid undue burdens on women often tasked with collecting wood for fuel, bring health benefits from reduced air pollution and proper waste management, and reduce methane emissions from inefficient combustion and waste decomposition. More generally, sustainable bioenergy can provide a valuable source of employment and income for rural communities in emerging economies." IEA 2021a.

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 '''Biomass (for energy)''' is matter from recently living (but now dead) organisms which is used for [[bioenergy]] production. Examples include wood, wood residues, [[energy crop]]s, agricultural residues, and [[Biodegradable waste|organic waste]] from industry and households.{{sfn|EIA|2021a}} Wood and wood residues is the largest biomass energy source today. Wood can be used as a fuel directly or processed into [[pellet fuel]] or other forms of fuels. Other plants can also be used as fuel, for instance [[corn]], [[switchgrass]], [[miscanthus]] and [[bamboo]].<ref>{{cite web |last1=Darby |first1=Thomas |title=What Is Biomass Renewable Energy |url=http://www.realworldenergy.com/what-is-biomass-renewable-energy/ |url-status=dead |archive-url=https://web.archive.org/web/20140608020208/http://realworldenergy.com/what-is-biomass-renewable-energy/ |archive-date=2014-06-08 |access-date=12 June 2014 |website=Real World Energy}}</ref> The main [[Waste energy|waste]] feedstocks are wood waste, [[agricultural waste]], [[municipal solid waste]], and [[manufacturing waste]]. Upgrading raw biomass to higher grade fuels can be achieved by different methods, broadly classified as thermal, chemical, or biochemical.
+The climate impact of bioenergy varies considerably depending on where biomass feedstocks come from and how they are grown.<ref name=":02">{{Cite journal |last1=Correa |first1=Diego F. |last2=Beyer |first2=Hawthorne L. |last3=Fargione |first3=Joseph E. |last4=Hill |first4=Jason D. |last5=Possingham |first5=Hugh P. |last6=Thomas-Hall |first6=Skye R. |last7=Schenk |first7=Peer M. |display-authors=4 |date=2019 |title=Towards the implementation of sustainable biofuel production systems |url=https://www.sciencedirect.com/science/article/pii/S136403211930139X |url-status=live |journal=[[Renewable and Sustainable Energy Reviews]] |volume=107 |pages=250–263 |doi=10.1016/j.rser.2019.03.005 |issn=1364-0321 |archive-url=https://web.archive.org/web/20210717132735/https://www.sciencedirect.com/science/article/abs/pii/S136403211930139X |archive-date=17 July 2021 |access-date=7 February 2021 |s2cid=117472901}}</ref> For example, burning wood for energy releases carbon dioxide; those emissions can be significantly offset if the trees that were harvested are replaced by new trees in a well-managed forest, as the new trees will absorb carbon dioxide from the air as they grow.<ref>{{Cite web |last=Daley |first=Jason |date=24 April 2018 |title=The EPA Declared That Burning Wood Is Carbon Neutral. It's Actually a Lot More Complicated |url=https://www.smithsonianmag.com/smart-news/epa-declares-burning-wood-carbon-neutral-180968880/ |url-status=live |archive-url=https://web.archive.org/web/20210630153427/https://www.smithsonianmag.com/smart-news/epa-declares-burning-wood-carbon-neutral-180968880/ |archive-date=30 June 2021 |access-date=2021-09-14 |website=[[Smithsonian Magazine]]}}</ref> However, the establishment and cultivation of bioenergy crops can [[Land use, land-use change, and forestry|displace natural ecosystems]], [[Soil retrogression and degradation|degrade soils]], and consume water resources and synthetic fertilisers.{{sfn|Tester|2012|p=512}}{{sfn|Smil|2017a|p=162}}
 In 2020 biomass produced 58 EJ ([[exajoule]]s) of energy, compared to 172 EJ from [[crude oil]], 157 EJ from coal, 138 EJ from [[natural gas]], 29 EJ from nuclear, 16 EJ from [[hydropower|hydro]] and 15 EJ from [[wind power|wind]], [[solar power|solar]] and [[geothermal energy|geothermal]] combined.<ref>{{Cite web |title=Energy Statistics Data Browser – Data Tools |url=https://www.iea.org/data-and-statistics/data-tools/energy-statistics-data-browser |access-date=2022-12-27 |website=IEA |language=en-GB}}</ref>{{efn|name=IEAdata2020-a}} Approximately 86% of modern bioenergy is used for heating applications, with 9% used for [[transport]] and 5% for [[electricity production|electricity]].{{efn|name=IEAdata2020-b}} Most of the global bioenergy is produced from forest resources.{{efn|name=bioenergy-statistics-2019-3-a}}
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 ==Climate impacts==
-Currently there is a lively debate going on about the real carbon intensity of a number of bioenergy pathways, especially from forestry. The critics are especially concerned about short-term or medium-term climate effects. Critics have emerged both among researchers{{efn|name=EASAC-2017-2-a}} and environmental activists.{{efn|name=Ambrose-2021}}{{efn|name=Grunwald-2021}} At the same time, bioenergy supporters in influential research organizations like the IPCC, IEA, and EU's Joint Research Centre argue that bioenergy is climate friendly when implemented correctly and at an appropriate scale. For instance in 2022, IEA stated that "bioenergy is an important pillar of decarbonisation in the energy transition as a near zero-emission fuel", and that "more efforts are needed to accelerate modern bioenergy deployment to get on track with the Net Zero Scenario [....] while simultaneously ensuring that bioenergy production does not incur negative social and environmental consequences."<ref>{{Cite web |date=September 2022 |title=Bioenergy – Energy system overview |url=https://www.iea.org/reports/bioenergy}}</ref>
+Currently there is a lively debate going on about the real carbon intensity of a number of bioenergy pathways, especially from forestry. The critics are especially concerned about short-term or medium-term climate effects. Critics have emerged both among researchers{{efn|name=EASAC-2017-2-a}} and environmental activists.{{efn|name=Ambrose-2021}}{{efn|name=Grunwald-2021}} At the same time, bioenergy supporters in influential research organizations like the IPCC, IEA, and EU's Joint Research Centre argue that bioenergy is climate friendly when implemented correctly and at an appropriate scale.
 {{excerpt|Sustainable energy#Bioenergy|paragraphs=2-4|file=no}}
@@ Line 193: / Line 195: @@
 == Environmental impacts ==
+The environmental impacts of biomass production need to be taken into account. For instance in 2022, IEA stated that "bioenergy is an important pillar of decarbonisation in the energy transition as a near zero-emission fuel", and that "more efforts are needed to accelerate modern bioenergy deployment to get on track with the Net Zero Scenario [....] while simultaneously ensuring that bioenergy production does not incur negative social and environmental consequences."<ref>{{Cite web |date=September 2022 |title=Bioenergy – Energy system overview |url=https://www.iea.org/reports/bioenergy}}</ref>
 ===Surface power production densities===

v t e Bioenergy
Biofuels	Alcohol Algae Babassu oil Bagasse Biobutanol Biodiesel Biogas Biogasoline Bioliquids Biomass Cooking oil vegetable oil Ethanol cellulosic mixtures Methanol Stover corn Straw Water hyacinth Wood gas
Energy from foodstock	Camelina sativa Cassava Coconut oil Grape Hemp Maize Oat Palm oil Potato Rapeseed Rice Sorghum Soybean Sugar beet Sugarcane Sunflower Wheat Yam
Non-food energy crops	Arundo Big bluestem Camelina Chinese tallow Duckweed Jatropha curcas Miscanthus × giganteus Pongamia pinnata Salicornia Switchgrass Wood
Technology	Bioconversion of biomass to mixed alcohol fuels Bioenergy with carbon capture and storage Biomass heating systems Biorefinery Fischer–Tropsch process Industrial biotechnology Pellet fuel mill stove Sabatier reaction Thermal depolymerization
Concepts	Agflation Cellulosic ethanol commercialization Energy content of biofuel Energy crop Energy forestry Energy return on investment Food vs. fuel Issues relating to biofuels Sustainable biofuel
Category

v t e Forestry
Index Forest areas Ministries Research institutes Colleges Journals Arbor Day
Types	Agroforestry dehesa Analog forestry Bamboo forestry Close to nature forestry Community forestry Ecoforestry Energy forestry Mycoforestry Permaforestry Plantation forestry Social forestry Sustainable forestry Urban forest Urban forestry
Ecology and management	Arboriculture Controlled burn Debris coarse driftwood large log jam slash Dendrology Ecological thinning Even-aged management Fire ecology Forest dynamics informatics IPM inventory governance law Global Forest Information Service old-growth pathology protection restoration secondary stand transition Trillion Tree Campaign Forest certification ATFS CFS FSC PEFC SFI SmartWood Woodland Carbon Code Forestation afforestation reforestation Formally designated Growth and yield modelling Horticulture GM trees i-Tree urban Silviculture Sustainable management Tree allometry breeding Tree measurement crown girth height volume
Environmental topics	Acid rain Carbon sequestration Clearcutting Deforestation Ecosystem services Forest degradation Forest dieback Forest fragmentation Ghost forest Great Green Wall (Africa) Great Green Wall (China) High grading Illegal logging timber mafia Invasive species wilding Million Tree Initiative REDD Shifting cultivation chitemene slash-and-burn slash-and-char svedjebruk Timber recycling Tree hugging Urban forest inequity Wildfire
Industries	Coppicing Forest farming Forest gardening Logging Manufacturing lumber plywood pulp and paper sawmilling Products biochar biomass charcoal non-timber palm oil rayon rubber tanbark Rail transport Tree farm Christmas trees Wood engineered fuel mahogany spruce-pine-fir teak Woodworking green woodworking
Occupations	Forester Arborist Bucker Choker setter Ecologist Feller Firefighter handcrew hotshot lookout smokejumper River driver Truck driver Log scaler Lumberjack Ranger Resin tapper Rubber tapper Shingle weaver Timber cruiser Tree planter Wood process engineer
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