Atlantic multidecadal oscillation: Difference between revisions

[[File:AMO Pattern.png|thumb|320px|Atlantic multidecadal oscillation spatial pattern obtained as the regression of monthly HadISST sea surface temperature anomalies (1870-20131870–2013).]]

[[File:Atlantic Multidecadal Oscillation.svg|thumb|320px|Atlantic Multidecadal Oscillation Index according to the methodology proposed by van Oldenborgh et al. 1880-20181880–2018.]]

[[File:Amo timeseries 1856-present.svg|thumb|320px|Atlantic Multidecadal Oscillation index computed as the linearly detrended North Atlantic sea surface temperature anomalies 1856-20131856–2022.]]

The '''Atlantic Multidecadal Oscillation''' ('''AMO'''), also known as '''Atlantic Multidecadal Variability''' ('''AMV'''),<ref>{{cite web |title=Multidecadal Climate Changes |url=https://www.gfdl.noaa.gov/multidecadal-climate-changes/ |publisher=Geophysical Fluid Dynamics Laboratory}}</ref> is the theorized [[Mode of variability|variability]] of the [[sea surface temperature]] (SST) of the [[North Atlantic Ocean]] on the timescale of several decades.<ref>{{cite journal|url=http://physmural.orgmaynoothuniversity.ie/12187/news1/2015-05-global-climate-verge-multi-decadalMcCarthy_Ocean_2015.htmlpdf|doi=10.1038/nature14491|author=Gerard D. McCarthy|author2=Ivan D. Haigh|author3=Joël J.M. Hirschi|author4=Jeremy P. Grist|author5=David A. Smeed|name-list-style=amp|date=27 May 2015|journal=Nature|title=Ocean impact on decadal Atlantic climate variability revealed by sea-level observations|bibcode = 2015Natur.521..508M|volume=521|issue=7553|pages=508–510|pmid=26017453|s2cid=4399436}}</ref>

While there is some support for this mode in models and in historical observations, controversy exists with regard to its [[amplitude]], and whether it has a typical timescale and can be classified as an oscillation. There is also discussion on the attribution of sea surface temperature change to natural or [[wikt:anthropogenic|anthropogenic]] causes, especially in tropical Atlantic areas important for hurricane development.<ref name="Ting 2009" /> The Atlantic multidecadal oscillation is also connected with shifts in hurricane activity, rainfall patterns and intensity, and changes in fish populations.<ref name="Frajka-Williams">{{cite journal|doi=10.1038/s41598-017-11046-x|pmid=28894211|pmc=5593924|authorsauthor1=Eleanor Frajka-Williams, |author2=Claudie Beaulieu & |author3=Aurelie Duchez |title=Emerging negative Atlantic Multidecadal Oscillation index in spite of warm subtropics|journal=Scientific Reports|volume=7|issue=1|pages=11224|year=2017|bibcode=2017NatSR...711224F}}</ref>

Evidence for a multidecadal climate oscillation centered in the North Atlantic began to emerge in 1980s work by Folland and colleagues, seen in Fig. 2.d.A.<ref>{{Cite journal|last1=Folland |first1=C. K. | last2=Parker |first2 =D .E. | last3=Kates |first3=F. E. |year=1984 |title=Worldwide marine temperature fluctuations 1856-19811856–1981 |journal=[[Nature (journal)|Nature]] |volume=310 |issue=5979 |pages=670–673 |doi=10.1038/310670a0 |bibcode = 1984Natur.310..670F |s2cid=4246538 }}</ref> That oscillation was the sole focus of Schlesinger and Ramankutty in 1994,<ref>{{Cite journal|last=Schlesinger |first=M. E. |year=1994 |title=An oscillation in the global climate system of period 65-7065–70 years |journal=[[Nature (journal)|Nature]] |volume=367 |issue=6465 |pages=723–726 |doi=10.1038/367723a0 |bibcode = 1994Natur.367..723S |s2cid=4351411 }}</ref> but the actual term Atlantic Multidecadal Oscillation (AMO) was coined by Michael Mann in a 2000 telephone interview with Richard Kerr,<ref>{{Cite journal|last1=Kerr |first1=Richard C. |year=2000 |title=A North Atlantic Climate Pacemaker for the Centuries |journal=[[Science (journal)|Science]] |volume=288 |issue=5473 |pages=1984–1985 |doi= 10.1126/science.288.5473.1984 |pmid=17835110 |s2cid=21968248 }}</ref> as recounted by Mann, p.&nbsp;30 in ''[[The Hockey Stick and the Climate Wars|The Hockey Stick and the Climate Wars: Dispatches from the Front Lines]]'' (2012).

The AMO signal is usually defined from the patterns of SST variability in the North Atlantic once any linear trend has been removed. This detrending is intended to remove the influence of [[greenhouse gas]]-induced [[global warming]] from the analysis. However, if the global warming signal is significantly non-linear in time (i.e. not just a smooth linear increase), variations in the forced signal will leak into the AMO definition. Consequently, correlations with the AMO index may mask effects of [[global warming]], as per Mann, Steinman and Miller,<ref name="mann 2014">{{Cite journal|last=Mann|first=Michael|author2=Byron A. Steinman|author3=Sonya K. Miller|title=On forced temperature changes, internal variability, and the AMO|journal=Geophysical Research Letters|year=2014|volume=41|issue=9|doi=10.1002/2014GL059233|pages=3211–3219|bibcode=2014GeoRL..41.3211M|doi-access=free|citeseerx=10.1.1.638.256}}<!--|access-date=19 September 2016--></ref> which also provides a more detailed history of the science development.

Guan and Nigam removed the non stationary global trend and Pacific natural variability before applying an [[Empirical orthogonal functions|EOF]] analysis to the residual North Atlantic SST.<ref name="guan 2009">{{Cite journal|last=Guan|first=Bin|author2=Sumant Nigam|s2cid=16792059|title=Analysis of Atlantic SST Variability Factoring Interbasin Links and the Secular Trend: Clarified Structure of the Atlantic Multidecadal Oscillation|journal=J. Climate|year=2009|volume=22|issue=15|pages=4228–4240|doi=10.1175/2009JCLI2921.1|bibcode = 2009JCli...22.4228G |doi-access=free}}<!--|access-date=17 March 2012--></ref>

A 2008 study correlated the Atlantic Multidecadal Mode (AMM), with [[HURDAT]] data (1851–2007), and noted a positive linear trend for minor hurricanes (category 1 and 2), but removed when the authors adjusted their model for undercounted storms, and stated "If there is an increase in hurricane activity connected to a greenhouse gas induced global warming, it is currently obscured by the 60 year quasi-periodic cycle."<ref name="Chylek/Lesins 2007">{{Cite journal |last1=Chylek |first1=P. |last2=Lesins |first2=G. |name-list-style=amp |year=2008 |title=Multidecadal variability of Atlantic hurricane activity: 1851–2007 |journal=[[Journal of Geophysical Research]] |volume=113 |issue=D22 |pages=D22106 |doi=10.1029/2008JD010036 |bibcode=2008JGRD..11322106C|url=https://zenodo.org/record/1231299 |doi-access=free }}</ref> With full consideration of meteorological science, the number of tropical storms that can mature into severe hurricanes is much greater during warm phases of the AMO than during cool phases, at least twice as many; the AMO is reflected in the frequency of severe Atlantic hurricanes.<ref name="National Oceanic and Atmospheric Administration">{{Cite web|title=National Oceanic and Atmospheric Administration Frequently Asked Questions about the Atlantic Multidecadal Oscillation |url=http://www.aoml.noaa.gov/phod/amo_faq.php |url-status=dead |archive-url=https://web.archive.org/web/20051126030955/http://www.aoml.noaa.gov/phod/amo_faq.php |archive-date=2005-11-26 }}</ref> Based on the typical duration of negative and positive phases of the AMO, the current warm regime is expected to persist at least until 2015 and possibly as late as 2035. Enfield ''et al.'' assume a peak around 2020.<ref name="Enfield2009">{{Cite journal|last1=Enfield|first1=David B.|last2=Cid-Serrano|first2=Luis|year=2010|title=Secular and multidecadal warmings in the North Atlantic and their relationships with major hurricane activity|journal=International Journal of Climatology|volume=30|issue=2|pages=174–184|doi=10.1002/joc.1881|bibcode=2010IJCli..30..174E |s2cid=18833210}}</ref>

However, Mann and Emanuel had found in 2006 that “anthropogenic"anthropogenic factors are responsible for long-term trends in tropic Atlantic warmth and tropical cyclone activity”activity" and “There"There is no apparent role of the AMO.”"<ref>{{Cite journal|last1=Mann |first1=M. E.|last2=Emanuel |first2=K. A. |s2cid=128633734|year=2006 |title=Atlantic Hurricane Trends Linked to Climate Change |journal=[[EOS (journal)|EOS]] |volume=87 |issue=24 |pages=233–244 |doi=10.1029/2006EO240001 |bibcode=2006EOSTr..87..233M|doi-access=free }}</ref>

In 2014 Mann, Steinman and Miller<ref name="mann 2014">{{Cite journal|last=Mann|first=Michael|author2=Byron A. Steinman|author3=Sonya K. Miller|title=On forced temperature changes, internal variability, and the AMO|journal=Geophysical Research Letters|year=2014|volume=41|issue=9|doi=10.1002/2014GL059233|pages=3211–3219|bibcode=2014GeoRL..41.3211M|doi-access=free|citeseerx=10.1.1.638.256}}<!--|access-date=19 September 2016--></ref> showed that warming (and therefore any effects on hurricanes) were not caused by the AMO, writing: "certain procedures used in past studies to estimate internal variability, and in particular, an internal multidecadal oscillation termed the “Atlantic"Atlantic Multidecadal Oscillation”Oscillation" or “AMO”"AMO", fail to isolate the true internal variability when it is a priori known. Such procedures yield an AMO signal with an inflated amplitude and biased phase, attributing some of the recent NH mean temperature rise to the AMO. The true AMO signal, instead, appears likely to have been in a cooling phase in recent decades, offsetting some of the anthropogenic warming."

There are only about 130–150 years of data based on instrument data, which are too few samples for conventional statistical approaches. With the aid of multi-century proxy reconstruction, a longer period of 424 years was used by Enfield and Cid–Serrano as an illustration of an approach as described in their paper called "The Probabilistic Projection of Climate Risk".<ref>{{cite web|url=http://old.usclivar.org/Newsletter/Variations_V3N3/Enfield.pdf |title=Archived copy |access-date=2014-08-23 |url-status=dead |archive-url=https://web.archive.org/web/20140826113823/http://old.usclivar.org/Newsletter/Variations_V3N3/Enfield.pdf |archive-date=2014-08-26 }}</ref> Their histogram of zero crossing intervals from a set of five re-sampled and smoothed version of Gray et al. (2004) index together with the [[maximum likelihood estimate]] gamma distribution fit to the histogram, showed that the largest frequency of regime interval was around 10–20 year. The cumulative probability for all intervals 20 years or less was about 70%.{{cncitation needed|date=April 2023}}

In a 2021 study by Michael Mann and others, it was shown that the periodicity of the AMO in the last millennium was driven by [[Types of volcanic eruptions|volcanic eruptions]] and other external forcings, and therefore that there is no compelling evidence for the AMO being an oscillation or cycle.<ref>{{Cite journal|last1=Mann|first1=Michael E.|last2=Steinman|first2=Byron A.|last3=Brouillette|first3=Daniel J.|last4=Miller|first4=Sonya K.|date=2021-03-05|title=Multidecadal climate oscillations during the past millennium driven by volcanic forcing|url=https://wwwscholarsphere.sciencepsu.orgedu/doiresources/10.1126/science.abc58109b2bee60-058c-4841-ba8a-271b20bbb906|journal=Science|language=en|volume=371|issue=6533|pages=1014–1019|doi=10.1126/science.abc5810|pmid=33674487|bibcode=2021Sci...371.1014M|s2cid=232124643|issn=0036-8075}}</ref> There was also a lack of oscillatory behaviour in models on time scales longer than El Niño Southern Oscillation; the AMV is indistinguishable from [[red noise]], a typical null hypothesis to test whether there are oscillations in a model.<ref>{{Cite journal|last1=Mann|first1=Michael E.|last2=Steinman|first2=Byron A.|last3=Miller|first3=Sonya K.|date=2020-01-03|title=Absence of internal multidecadal and interdecadal oscillations in climate model simulations|journal=Nature Communications|language=en|volume=11|issue=1|pages=49|doi=10.1038/s41467-019-13823-w|pmid=31900412|pmc=6941994|bibcode=2020NatCo..11...49M|issn=2041-1723|doi-access=free}}</ref> Referring to the 2021 study, Michael Mann, the originator of the term AMO, put it more succinctly in a blog post on the matter: "my colleagues and I have provided what we consider to be the most definitive evidence yet that the AMO doesn't actually exist."<ref>{{cite web |last1=Mann |first1=Michael |title=The Rise and Fall of the "Atlantic Multidecadal Oscillation" |url=https://michaelmann.net/content/rise-and-fall-atlantic-multidecadal-oscillation |website=michaelmann.net |date=11 February 2021 |access-date=14 September 2023}}</ref>

* {{cite journal |last=Goldenberg |first=S. B. |year=2001 |title=The recent increase in Atlantic hurricane activity: Causes and implications |journal=[[Science (journal)|Science]] |volume=293 |issue= 5529|pages=474–479 |doi=10.1126/science.1060040 |pmid=11463911|bibcode = 2001Sci...293..474G |s2cid=29147811 |doi-access=free }}

* {{cite journal |last=Kerr |first=R. A. |year=2005 |title=Atlantic climate pacemaker for millennia past, decades hence? |journal=Science |volume=309 |issue=5731 |pages=41–43 |doi=10.1126/science.309.5731.41 |pmid=15994503|s2cid=40555628 |doi-access=free }}

* {{cite journal |last=Knight |first=J. R. |s2cid=16909466 |year=2005 |title=A signature of persistent natural thermohaline circulation cycles in observed climate |journal=Geophys. Res. Lett. |volume=32 |issue= 20|pages=L20708 |doi=10.1029/2005GL024233 |bibcode=2005GeoRL..3220708K|doi-access=free }}

* {{cite journal |last1=Sutton |first1=R. T. |last2=Hodson |first2=L. R. |year=2005 |title=Atlantic forcing of North American and European summer climate |journal=Science |volume=309 |issue= 5731|pages=115–118 |doi=10.1126/science.1109496 |pmid=15994552|bibcode = 2005Sci...309..115S |s2cid=19372166 |doi-access=free }}