Editing Climate variability and change (section)

=== Internal variability ===
[[File:1951+ Percent of global area at temperature records - Seasonal comparison - NOAA.svg |thumb |upright=1.35 |There is seasonal variability in how new high temperature records have outpaced new low temperature records.<ref name="NCEI_NOAA-2023">{{cite web |title=Mean Monthly Temperature Records Across the Globe / Timeseries of Global Land and Ocean Areas at Record Levels for October from 1951–2023 |url=https://www.ncei.noaa.gov/access/monitoring/monthly-report/global/202310/supplemental/page-3 |website=NCEI.NOAA.gov |publisher=National Centers for Environmental Information (NCEI) of the National Oceanic and Atmospheric Administration (NOAA)|archive-url=https://web.archive.org/web/20231116185412/https://www.ncei.noaa.gov/access/monitoring/monthly-report/global/202310/supplemental/page-3 |archive-date=16 November 2023 |date=November 2023 |url-status=live}} (change "202310" in URL to see years other than 2023, and months other than 10=October)</ref>]]

Climatic changes due to internal variability sometimes occur in cycles or oscillations. For other types of natural climatic change, we cannot predict when it happens; the change is called ''random'' or ''stochastic''.{{Sfn|Ruddiman|2008|pp=261–62}} From a climate perspective, the weather can be considered random.<ref>{{Cite journal|last=Hasselmann|first=K.|date=1976|title=Stochastic climate models Part I. Theory|journal=Tellus|volume=28|issue=6|pages=473–85|doi=10.1111/j.2153-3490.1976.tb00696.x|issn=2153-3490|bibcode=1976Tell...28..473H}}</ref> If there are little clouds in a particular year, there is an energy imbalance and extra heat can be absorbed by the oceans. Due to [[climate inertia]], this signal can be 'stored' in the ocean and be expressed as variability on longer time scales than the original weather disturbances.<ref>{{Cite journal|last=Liu|first=Zhengyu|s2cid=53953041|date=14 October 2011|title=Dynamics of Interdecadal Climate Variability: A Historical Perspective|journal=Journal of Climate|volume=25|issue=6|pages=1963–95|doi=10.1175/2011JCLI3980.1|issn=0894-8755|doi-access=free}}</ref> If the weather disturbances are completely random, occurring as [[white noise]], the inertia of glaciers or oceans can transform this into climate changes where longer-duration oscillations are also larger oscillations, a phenomenon called [[red noise]].{{Sfn|Ruddiman|2008|p=262}} Many climate changes have a random aspect and a cyclical aspect. This behavior is dubbed ''[[stochastic resonance]]''.{{Sfn|Ruddiman|2008|p=262}} Half of the [[List of Nobel laureates in Physics#Laureates|2021 Nobel prize on physics]] was awarded for this work to [[Klaus Hasselmann]] jointly with [[Syukuro Manabe]] for related work on [[climate model]]ling. While [[Giorgio Parisi]] who with collaborators introduced<ref>{{cite journal|vauthors=Benzi R, Parisi G, Sutera A, Vulpiani A|year=1982|title=Stochastic resonance in climatic change|journal=Tellus|volume=34|issue=1|pages=10–6|bibcode=1982Tell...34...10B|doi=10.1111/j.2153-3490.1982.tb01787.x|url=https://www.openaccessrepository.it/record/123925 |archive-url=https://web.archive.org/web/20241201230816/https://www.openaccessrepository.it/record/123925 |url-status=dead |archive-date=1 December 2024 |url-access=subscription}}</ref> the concept of stochastic resonance was awarded the other half but mainly for work on theoretical physics.

==== Ocean-atmosphere variability ====
The ocean and atmosphere can work together to spontaneously generate internal climate variability that can persist for years to decades at a time.<ref>{{cite journal |last1=Brown |first1=Patrick T. |last2=Li |first2=Wenhong |last3=Cordero |first3=Eugene C. |last4=Mauget |first4=Steven A. |date=21 April 2015 |title=Comparing the model-simulated global warming signal to observations using empirical estimates of unforced noise |journal=Scientific Reports |issn=2045-2322 |doi=10.1038/srep09957 |pmc=4404682 |pmid=25898351 |volume=5|issue=1 |page=9957 |bibcode=2015NatSR...5.9957B }}</ref><ref>{{cite journal |last=Hasselmann |first=K. |date=1 December 1976 |title=Stochastic climate models Part I. Theory |journal=Tellus |issn=2153-3490 |doi=10.1111/j.2153-3490.1976.tb00696.x |volume=28 |issue=6 |pages=473–85 |bibcode=1976Tell...28..473H }}</ref> These variations can affect global average surface temperature by redistributing heat between the deep ocean and the atmosphere<ref>{{cite journal |last1=Meehl |first1=Gerald A. |last2=Hu |first2=Aixue |last3=Arblaster |first3=Julie M. |last4=Fasullo |first4=John |last5=Trenberth |first5=Kevin E. |s2cid=16183172 |date=8 April 2013 |title=Externally Forced and Internally Generated Decadal Climate Variability Associated with the Interdecadal Pacific Oscillation |journal=Journal of Climate |issn=0894-8755 |doi=10.1175/JCLI-D-12-00548.1 |volume=26 |issue=18 |pages=7298–310 |bibcode=2013JCli...26.7298M |osti=1565088 |url=https://zenodo.org/record/1234599 |access-date=5 June 2020 |archive-date=11 March 2023 |archive-url=https://web.archive.org/web/20230311124210/https://zenodo.org/record/1234599 |url-status=live |doi-access=free }}</ref><ref>{{cite journal |last1=England |first1=Matthew H. |last2=McGregor |first2=Shayne |last3=Spence |first3=Paul |last4=Meehl |first4=Gerald A. |last5=Timmermann |first5=Axel |author-link5= Axel Timmermann |last6=Cai |first6=Wenju |last7=Gupta |first7=Alex Sen |last8=McPhaden |first8=Michael J. |last9=Purich |first9=Ariaan |date=1 March 2014 |title=Recent intensification of wind-driven circulation in the Pacific and the ongoing warming hiatus |journal=Nature Climate Change |issn=1758-678X |doi=10.1038/nclimate2106 |volume=4 |issue=3 |pages=222–27|bibcode=2014NatCC...4..222E }}</ref> and/or by altering the cloud/water vapor/sea ice distribution which can affect the total energy budget of the Earth.<ref>{{cite journal |last1=Brown |first1=Patrick T. |last2=Li |first2=Wenhong |last3=Li |first3=Laifang |last4=Ming |first4=Yi |date=28 July 2014 |title=Top-of-atmosphere radiative contribution to unforced decadal global temperature variability in climate models |journal=Geophysical Research Letters |issn=1944-8007 |doi=10.1002/2014GL060625 |volume=41 |issue=14 |page=2014GL060625 |bibcode=2014GeoRL..41.5175B |hdl=10161/9167 |s2cid=16933795 |hdl-access=free }}</ref><ref>{{cite journal |last1=Palmer |first1=M. D. |last2=McNeall |first2=D. J. |date=1 January 2014 |title=Internal variability of Earth's energy budget simulated by CMIP5 climate models |journal=Environmental Research Letters |issn=1748-9326 |doi=10.1088/1748-9326/9/3/034016 |volume=9 |issue=3 |page=034016 |bibcode=2014ERL.....9c4016P |doi-access=free }}</ref>

==== Oscillations and cycles {{anchor|Oscillations|Cycles}} ====
[[File:20210827 Global surface temperature bar chart - bars color-coded by El Niño and La Niña intensity.svg|thumb| upright=1.25|Colored bars show how El Niño years (red, regional warming) and La Niña years (blue, regional cooling) relate to overall [[global surface temperature|global warming]]. The [[El Niño–Southern Oscillation]] has been linked to variability in longer-term global average temperature increase.]]
A ''climate oscillation'' or ''climate cycle'' is any recurring cyclical [[oscillation]] within global or regional [[climate]]. They are [[quasiperiodic]] (not perfectly periodic), so a [[Fourier analysis]] of the data does not have sharp peaks in the [[spectral density estimation|spectrum]]. Many oscillations on different time-scales have been found or hypothesized:<ref>{{Cite web|url=https://www.whoi.edu/main/topic/el-nino-other-oscillations|title=El Niño & Other Oscillations|website=Woods Hole Oceanographic Institution|access-date=6 April 2019|archive-date=6 April 2019|archive-url=https://web.archive.org/web/20190406082544/https://www.whoi.edu/main/topic/el-nino-other-oscillations|url-status=live}}</ref>

* the [[El Niño–Southern Oscillation]] (ENSO) – A large scale pattern of warmer ([[El Niño]]) and colder ([[La Niña]]) tropical [[sea surface temperature]]s in the Pacific Ocean with worldwide effects. It is a self-sustaining oscillation, whose mechanisms are well-studied.<ref>{{Cite journal|last=Wang|first=Chunzai|date=2018|title=A review of ENSO theories|journal=National Science Review|volume=5|issue=6|pages=813–825|doi=10.1093/nsr/nwy104|issn=2095-5138|doi-access=free}}</ref> ENSO is the most prominent known source of inter-annual variability in weather and climate around the world. The cycle occurs every two to seven years, with El Niño lasting nine months to two years within the longer term cycle.<ref>{{cite web|url=http://www.cpc.noaa.gov/products/analysis_monitoring/ensostuff/ensofaq.shtml#HOWOFTEN|title=ENSO FAQ: How often do El Niño and La Niña typically occur?|author=Climate Prediction Center|date=19 December 2005|publisher=[[National Centers for Environmental Prediction]]|url-status=dead|archive-url=https://web.archive.org/web/20090827143632/http://www.cpc.noaa.gov/products/analysis_monitoring/ensostuff/ensofaq.shtml#HOWOFTEN|archive-date=27 August 2009|access-date=26 July 2009|author-link=Climate Prediction Center}}</ref> The cold tongue of the equatorial Pacific Ocean is not warming as fast as the rest of the ocean, due to increased [[upwelling]] of cold waters off the west coast of South America.<ref>{{cite web|url=https://lamont.columbia.edu/news/part-pacific-ocean-not-warming-expected-why|title=Part of the Pacific Ocean Is Not Warming as Expected. Why|author=Kevin Krajick|publisher=Columbia University Lamont-Doherty Earth Observatory|access-date=2 November 2022|archive-date=5 March 2023|archive-url=https://web.archive.org/web/20230305101155/https://lamont.columbia.edu/news/part-pacific-ocean-not-warming-expected-why|url-status=live}}</ref><ref>{{cite web|url=https://www.newsweek.com/mystery-stretch-pacific-ocean-warming-world-1445990?amp=1|title=Mystery Stretch of the Pacific Ocean Is Not Warming Like the Rest of the World's Waters|author=Aristos Georgiou|date=26 June 2019 |publisher=Newsweek|access-date=2 November 2022|archive-date=25 February 2023|archive-url=https://web.archive.org/web/20230225140142/https://www.newsweek.com/mystery-stretch-pacific-ocean-warming-world-1445990?amp=1|url-status=live}}</ref>
* the [[Madden–Julian oscillation]] (MJO) – An eastward moving pattern of increased rainfall over the tropics with a period of 30 to 60 days, observed mainly over the Indian and Pacific Oceans.<ref>{{Cite web|url=https://www.climate.gov/news-features/blogs/enso/what-mjo-and-why-do-we-care|title=What is the MJO, and why do we care?|website=NOAA Climate.gov|language=en|access-date=6 April 2019|archive-date=15 March 2023|archive-url=https://web.archive.org/web/20230315025156/https://www.climate.gov/news-features/blogs/enso/what-mjo-and-why-do-we-care|url-status=live}}</ref>
* the [[North Atlantic oscillation]] (NAO) – Indices of the [[North Atlantic oscillation|NAO]] are based on the difference of normalized [[sea-level pressure]] (SLP) between [[Ponta Delgada|Ponta Delgada, Azores]] and [[Stykkishólmur]]/[[Reykjavík]], Iceland. Positive values of the index indicate stronger-than-average westerlies over the middle latitudes.<ref name="NCAR">National Center for Atmospheric Research. [http://www.cgd.ucar.edu/cas/jhurrell/indices.info.html Climate Analysis Section.] {{webarchive|url=https://web.archive.org/web/20060622232926/http://www.cgd.ucar.edu/cas/jhurrell/indices.info.html|date=22 June 2006}} Retrieved on 7 June 2007.</ref>
* the [[Quasi-biennial oscillation]] – a well-understood oscillation in wind patterns in the [[stratosphere]] around the equator. Over a period of 28 months the dominant wind changes from easterly to westerly and back.<ref>{{Cite journal|last1=Baldwin|first1=M. P.|last2=Gray|first2=L. J.|last3=Dunkerton|first3=T. J.|last4=Hamilton|first4=K.|last5=Haynes|first5=P. H.|last6=Randel|first6=W. J.|last7=Holton|first7=J. R.|last8=Alexander|first8=M. J.|last9=Hirota|first9=I.|s2cid=16727059|date=2001|title=The quasi-biennial oscillation|journal=Reviews of Geophysics|language=en|volume=39|issue=2|pages=179–229|doi=10.1029/1999RG000073|bibcode=2001RvGeo..39..179B|doi-access=free}}</ref>
* [[Pacific Centennial Oscillation]] - a [[climate oscillation]] predicted by some [[climate model]]s
* the [[Pacific decadal oscillation]] – The dominant pattern of sea surface variability in the North Pacific on a decadal scale. During a "warm", or "positive", phase, the west Pacific becomes cool and part of the eastern ocean warms; during a "cool" or "negative" phase, the opposite pattern occurs. It is thought not as a single phenomenon, but instead a combination of different physical processes.<ref>{{Cite journal|last1=Newman|first1=Matthew|last2=Alexander|first2=Michael A.|last3=Ault|first3=Toby R.|last4=Cobb|first4=Kim M.|last5=Deser|first5=Clara|last6=Di Lorenzo|first6=Emanuele|last7=Mantua|first7=Nathan J.|last8=Miller|first8=Arthur J.|last9=Minobe|first9=Shoshiro|s2cid=4824093|date=2016|title=The Pacific Decadal Oscillation, Revisited|journal=Journal of Climate|volume=29|issue=12|pages=4399–4427|doi=10.1175/JCLI-D-15-0508.1|issn=0894-8755|bibcode=2016JCli...29.4399N}}</ref>
* the [[Interdecadal Pacific oscillation]] (IPO) – Basin wide variability in the Pacific Ocean with a period between 20 and 30 years.<ref>{{Cite web|url=https://www.niwa.co.nz/node/111124|title=Interdecadal Pacific Oscillation|date=19 January 2016|website=NIWA|language=en|access-date=6 April 2019|archive-date=17 March 2023|archive-url=https://web.archive.org/web/20230317140832/https://niwa.co.nz/node/111124|url-status=live}}</ref>
* the [[Atlantic multidecadal oscillation]] – A pattern of variability in the North Atlantic of about 55 to 70 years, with effects on rainfall, droughts and hurricane frequency and intensity.<ref>{{Cite journal|last1=Kuijpers|first1=Antoon|last2=Bo Holm Jacobsen|last3=Seidenkrantz|first3=Marit-Solveig|last4=Knudsen|first4=Mads Faurschou|date=2011|title=Tracking the Atlantic Multidecadal Oscillation through the last 8,000 years|journal=Nature Communications|language=en|volume=2|issue=1 |pages=178–|doi=10.1038/ncomms1186|pmid=21285956|issn=2041-1723|pmc=3105344|bibcode=2011NatCo...2..178K}}</ref>
* [[North African climate cycles]] – climate variation driven by the [[North African Monsoon]], with a period of tens of thousands of years.<ref>{{cite journal|last1=Skonieczny|first1=C.|date=2 January 2019|title=Monsoon-driven Saharan dust variability over the past 240,000 years|journal=Science Advances|volume=5|issue=1|pages=eaav1887|doi=10.1126/sciadv.aav1887|pmc=6314818|pmid=30613782|bibcode=2019SciA....5.1887S}}</ref>
* the [[Arctic oscillation]] (AO) and [[Antarctic oscillation]] (AAO) – The annular modes are naturally occurring, hemispheric-wide patterns of climate variability. On timescales of weeks to months they explain 20–30% of the variability in their respective hemispheres. The Northern Annular Mode or [[Arctic oscillation]] (AO) in the Northern Hemisphere, and the Southern Annular Mode or [[Antarctic oscillation]] (AAO) in the southern hemisphere. The annular modes have a strong influence on the temperature and precipitation of mid-to-high latitude land masses, such as Europe and Australia, by altering the average paths of storms. The NAO can be considered a regional index of the AO/NAM.<ref>{{cite web |last1=Thompson |first1=David |title=Annular Modes – Introduction |url=http://www.atmos.colostate.edu/~davet/ao/introduction.html |access-date=11 February 2020 |archive-date=18 March 2023 |archive-url=https://web.archive.org/web/20230318094533/https://www.atmos.colostate.edu/~davet/ao/introduction.html |url-status=live }}</ref> They are defined as the first [[Empirical orthogonal functions|EOF]] of sea level pressure or geopotential height from 20°N to 90°N (NAM) or 20°S to 90°S (SAM).
* [[Dansgaard–Oeschger cycles]] – occurring on roughly 1,500-year cycles during the [[Last Glacial Maximum]]

==== Ocean current changes ====
{{See also|Thermohaline circulation}}
[[File:Ocean circulation conveyor belt.jpg|thumb|right|upright=1.35|A schematic of modern [[thermohaline circulation]]. Tens of millions of years ago, continental-plate movement formed a land-free gap around Antarctica, allowing the formation of the [[Antarctic Circumpolar Current|ACC]], which keeps warm waters away from Antarctica.]]
The oceanic aspects of climate variability can generate variability on centennial timescales due to the ocean having hundreds of times more mass than in the [[Atmosphere of Earth|atmosphere]], and thus very high [[thermal inertia]]. For example, alterations to ocean processes such as thermohaline circulation play a key role in redistributing heat in the world's oceans.

Ocean currents transport a lot of energy from the warm tropical regions to the colder polar regions. Changes occurring around the last ice age (in technical terms, the last [[glacial period]]) show that the circulation in the [[North Atlantic]] can change suddenly and substantially, leading to global climate changes, even though the total amount of energy coming into the climate system did not change much. These large changes may have come from so called [[Heinrich events]] where internal instability of ice sheets caused huge ice bergs to be released into the ocean. When the ice sheet melts, the resulting water is very low in salt and cold, driving changes in circulation.{{sfn|Burroughs|2001|pp=207–08}}

==== Life ====
Life affects climate through its role in the [[carbon cycle|carbon]] and [[water cycle]]s and through such mechanisms as [[albedo]], [[evapotranspiration]], [[Cloud|cloud formation]], and [[weathering]].<ref>{{cite journal |last1=Spracklen |first1=D. V. |last2=Bonn |first2=B. |last3=Carslaw |first3=K. S. |year=2008 |title=Boreal forests, aerosols and the impacts on clouds and climate |journal=Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences |doi=10.1098/rsta.2008.0201 |pmid=18826917 |bibcode=2008RSPTA.366.4613S |volume=366 |issue=1885 |pages=4613–26 |s2cid=206156442 }}</ref><ref>{{cite journal |last1=Christner |first1=B. C. |last2=Morris |first2=C. E. |last3=Foreman |first3=C. M. |last4=Cai |first4=R. |last5=Sands |first5=D. C. |year=2008 |title=Ubiquity of Biological Ice Nucleators in Snowfall |journal=Science |doi=10.1126/science.1149757 |pmid=18309078 |bibcode=2008Sci...319.1214C |volume=319 |issue=5867 |page=1214 |s2cid=39398426 |url=https://scholarworks.montana.edu/xmlui/bitstream/1/13209/1/08-006_Ubiquity_of_biological.pdf |archive-url=https://web.archive.org/web/20200305072355/https://scholarworks.montana.edu/xmlui/bitstream/1/13209/1/08-006_Ubiquity_of_biological.pdf |archive-date=2020-03-05 |url-status=live }}</ref><ref>{{cite journal |last1=Schwartzman |first1=David W. |last2=Volk |first2=Tyler |year=1989 |title=Biotic enhancement of weathering and the habitability of Earth |journal=Nature |bibcode=1989Natur.340..457S |doi=10.1038/340457a0 |volume=340 |issue=6233 |pages=457–60 |s2cid=4314648 }}</ref> Examples of how life may have affected past climate include:
* [[glaciation]] 2.3 billion years ago triggered by the evolution of oxygenic [[photosynthesis]], which depleted the atmosphere of the greenhouse gas carbon dioxide and introduced free oxygen<ref>{{cite journal |doi=10.1073/pnas.0504878102 |title=The Paleoproterozoic snowball Earth: A climate disaster triggered by the evolution of oxygenic photosynthesis |year=2005 |last1=Kopp |first1=R.E. |last2=Kirschvink |first2=J.L. |last3=Hilburn |first3=I.A. |last4=Nash |first4=C.Z. |journal=Proceedings of the National Academy of Sciences |volume=102 |issue=32 |pages=11131–36 |pmid=16061801 |pmc=1183582|bibcode = 2005PNAS..10211131K |doi-access=free }}</ref><ref>{{cite journal |doi=10.1126/science.1071184 |title= Life and the Evolution of Earth's Atmosphere |year=2002 |last1= Kasting |first1=J.F. |journal= Science |volume=296 |issue=5570 |pages= 1066–68 |pmid=12004117 |last2=Siefert |first2=JL|s2cid=37190778 |bibcode = 2002Sci...296.1066K }}</ref>
* another glaciation 300 million years ago ushered in by long-term burial of [[lignin|decomposition-resistant]] [[detritus]] of vascular land-plants (creating a [[carbon sink]] and [[Coal#Formation|forming coal]])<ref>{{cite journal |doi=10.1126/science.271.5252.1105 |title= Middle to Late Paleozoic Atmospheric CO2 Levels from Soil Carbonate and Organic Matter |year=1996 |last1=Mora |first1=C.I. |last2=Driese |first2=S.G. |last3=Colarusso |first3=L. A. |journal=Science |volume=271 |issue=5252 |pages=1105–07 |bibcode= 1996Sci...271.1105M|s2cid=128479221 }}</ref><ref>{{cite journal |doi=10.1073/pnas.96.20.10955 |title=Atmospheric oxygen over Phanerozoic time |year=1999 |last1=Berner |first1=R.A. |journal=Proceedings of the National Academy of Sciences |volume=96 |issue=20 |pages= 10955–57 |pmid=10500106 |pmc=34224|bibcode = 1999PNAS...9610955B |doi-access=free }}</ref>
* termination of the [[Paleocene–Eocene Thermal Maximum]] 55 million years ago by flourishing marine [[phytoplankton]]<ref>{{cite journal |doi=10.1038/35025035 |year=2000 |last1=Bains |first1=Santo |last2=Norris |first2=Richard D. |last3=Corfield |first3=Richard M. |last4=Faul |first4=Kristina L. |journal=Nature |volume=407 |issue=6801 |pages=171–74 |pmid=11001051 |title=Termination of global warmth at the Palaeocene/Eocene boundary through productivity feedback|bibcode = 2000Natur.407..171B |s2cid=4419536 }}</ref><ref name="Zachos-2000">{{cite journal |doi=10.1080/11035890001221188 |title=An assessment of the biogeochemical feedback response to the climatic and chemical perturbations of the LPTM |year= 2000 |last1=Zachos |first1= J.C. |last2= Dickens |first2=G.R. |journal= GFF |volume=122 |issue=1 |pages=188–89|bibcode=2000GFF...122..188Z |s2cid=129797785 }}</ref>
* reversal of global warming 49 million years ago by [[Azolla event|800,000 years of arctic azolla blooms]]<ref>{{cite journal |doi=10.1111/j.1472-4669.2009.00195.x |title=The Eocene Arctic Azolla bloom: Environmental conditions, productivity and carbon drawdown |year=2009 |last1=Speelman |first1=E.N. |last2=Van Kempen |first2=M.M.L. |last3=Barke |first3=J. |last4=Brinkhuis |first4=H. |last5=Reichart |first5=G.J. |last6=Smolders |first6=A.J.P. |last7=Roelofs |first7=J.G.M. |last8=Sangiorgi |first8=F. |last9=De Leeuw |first9=J.W. |last10=Lotter |first10=A.F. |last11=Sinninghe Damsté |first11=J.S. |s2cid=13206343 |journal=Geobiology |volume=7 |issue=2 |pages=155–70 |pmid=19323694|bibcode=2009Gbio....7..155S }}</ref><ref>{{cite journal |doi=10.1038/nature04692 |title=Episodic fresh surface waters in the Eocene Arctic Ocean |year=2006 |last1=Brinkhuis |first1=Henk |last2=Schouten |first2=Stefan |last3=Collinson |first3=Margaret E. |last4=Sluijs |first4=Appy |last5=Sinninghe Damsté |first5=Jaap S. Sinninghe |last6=Dickens |first6=Gerald R. |last7=Huber |first7=Matthew |last8=Cronin |first8=Thomas M. |last9=Onodera |first9=Jonaotaro |last10=Takahashi |first10=Kozo |last11=Bujak |first11=Jonathan P. |last12=Stein |first12=Ruediger |last13=Van Der Burgh |first13=Johan |last14=Eldrett |first14=James S. |last15=Harding |first15=Ian C. |last16=Lotter |first16=André F. |last17=Sangiorgi |first17=Francesca |last18=Van Konijnenburg-Van Cittert |first18=Han van Konijnenburg-van |last19=De Leeuw |first19=Jan W. |last20=Matthiessen |first20=Jens |last21=Backman |first21=Jan |last22=Moran |first22=Kathryn |last23=Expedition 302 |journal=Nature |volume=441 |issue=7093 |pages=606–09 |pmid=16752440 |first23=Scientists|bibcode = 2006Natur.441..606B |hdl=11250/174278 |s2cid=4412107 |hdl-access=free }}</ref>
* global cooling over the past 40 million years driven by the expansion of grass-grazer [[ecosystem]]s<ref>{{cite journal |doi=10.1086/320791 |title=Cenozoic Expansion of Grasslands and Climatic Cooling |year=2001 |last1=Retallack |first1=Gregory J. |s2cid=15560105 |journal=The Journal of Geology |volume=109 |issue=4 |pages=407–26 |bibcode=2001JG....109..407R}}</ref><ref>{{cite journal |doi=10.1130/0091-7613(1997)025<0039:MTPVCA>2.3.CO;2 |title= Miocene to present vegetation changes: A possible piece of the Cenozoic cooling puzzle |year=1997 |last1=Dutton |first1=Jan F. |last2=Barron |first2=Eric J. |journal=Geology |volume=25 |issue= 1 |page=39|bibcode = 1997Geo....25...39D }}</ref>