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''Climate variability'' is the term to describe variations in the mean state and other characteristics of [[climate]] (such as chances or possibility of [[extreme weather]], etc.) "on all spatial and temporal scales beyond that of individual weather events."<!-- {{Sfn|IPCC AR5 WG1 Glossary|2013|p=1451}} puts page in [[:category:Harv and Sfn no-target errors]] --> Some of the variability does not appear to be caused by known systems and occurs at seemingly random times. Such variability is called ''random variability'' or ''[[Noise (signal processing)|noise]]''. On the other hand, periodic variability occurs relatively regularly and in distinct modes of variability or climate patterns.{{Sfn|Rohli|Vega|2018|p=274}}
The term ''climate change'' is often used to refer specifically to anthropogenic climate change (also known as [[global warming]]). Anthropogenic climate change is caused by human activity, as opposed to changes in climate that may have resulted as part of Earth's natural processes.<ref name=":2">{{cite web |date=21 March 1994 |title=The United Nations Framework Convention on Climate Change |url=http://unfccc.int/resource/ccsites/zimbab/conven/text/art01.htm |quote=''Climate change'' means a change of climate which is attributed directly or indirectly to human activity that alters the composition of the global atmosphere and which is in addition to natural climate variability observed over comparable time periods. |access-date=9 October 2018 |archive-date=20 September 2022 |archive-url=https://web.archive.org/web/20220920173907/https://unfccc.int/resource/ccsites/zimbab/conven/text/art01.htm |url-status=live }}</ref>
In this sense, the term climate change has become synonymous with [[human impact on the environment|anthropogenic]] [[global warming]]. Within scientific journals, global warming refers to surface temperature increases while climate change includes global warming and everything else that increasing [[greenhouse gas]] levels affect.<ref name=":3">{{cite web |title=What's in a Name? Global Warming vs. Climate Change |publisher=NASA |url=http://www.nasa.gov/topics/earth/features/climate_by_any_other_name.html |access-date=23 July 2011 |archive-date=9 August 2010 |archive-url=https://web.archive.org/web/20100809221926/http://www.nasa.gov/topics/earth/features/climate_by_any_other_name.html |url-status=live }}</ref>
A related term, ''climatic change'', was proposed by the [[World Meteorological Organization]] (WMO) in 1966 to encompass all forms of climatic variability on time-scales longer than 10 years, but regardless of cause. During the 1970s, the term climate change replaced climatic change to focus on anthropogenic causes, as it became clear that human activities had a potential to drastically alter the climate.<ref name=":1"/> Climate change was incorporated in the title of the [[Intergovernmental Panel on Climate Change]] (IPCC) and the [[UN Framework Convention on Climate Change]] (UNFCCC). Climate change is now used as both a technical description of the process, as well as a noun used to describe the problem.<ref name=":1">{{cite journal |last=Hulme |first=Mike |year=2016 |title=Concept of Climate Change, in: The International Encyclopedia of Geography |journal=The International Encyclopedia of Geography |page=1 |publisher=Wiley-Blackwell/Association of American Geographers (AAG) |url=https://www.academia.edu/10358797 |access-date=16 May 2016 |archive-date=29 September 2022 |archive-url=https://web.archive.org/web/20220929201908/https://www.academia.edu/10358797 |url-status=live }}</ref>
== Causes ==
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[[File:El Nino regional impacts.png|thumb|upright=1.35|El Niño impacts]]
[[File:La Nina regional impacts.gif|thumb|upright=1.35|La Niña impacts]]
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|page=9957 |bibcode=2015NatSR...5E9957B }}</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=1976TellA..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 }}</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}} ====
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 temperatures 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=
* 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?
* 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="CLIINDEX">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|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]]
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Whereas [[greenhouse gas]]es released by the biosphere is often seen as a feedback or internal climate process, greenhouse gases emitted from volcanoes are typically classified as external by climatologists.<ref>{{harvnb|Cronin|2010|p=17}}</ref> Greenhouse gases, such as {{CO2}}, methane and nitrous oxide, heat the climate system by trapping infrared light. Volcanoes are also part of the extended [[carbon cycle]]. Over very long (geological) time periods, they release carbon dioxide from the Earth's crust and mantle, counteracting the uptake by sedimentary rocks and other geological [[carbon dioxide sink]]s.
Since the [[industrial revolution]], humanity has been adding to greenhouse gases by emitting CO<sub>2</sub> from [[fossil fuel]] combustion, changing [[land use]] through deforestation, and has further altered the climate with [[aerosols]] (particulate matter in the atmosphere),<ref>{{cite web |url=https://www.science.org.au/learning/general-audience/science-booklets-0/science-climate-change/3-are-human-activities-causing |title=3. Are human activities causing climate change? |publisher=
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}}</ref> Other factors, including land use, [[ozone depletion]], animal husbandry ([[ruminant]] animals such as [[cattle]] produce [[methane]]<ref name="Steinfeld2006">{{cite book | last = Steinfeld | first = H. |author2=P. Gerber |author3=T. Wassenaar |author4=V. Castel |author5=M. Rosales |author6=C. de Haan | title = Livestock's long shadow | year = 2006 | url = http://www.fao.org/docrep/010/a0701e/a0701e00.HTM}}</ref>), and [[deforestation]], also play a role.<ref name="NYT-20151128">{{cite news |author=The Editorial Board |title=What the Paris Climate Meeting Must Do |url=https://www.nytimes.com/2015/11/29/opinion/sunday/what-the-paris-climate-meeting-must-do.html |date=28 November 2015 |work=[[The New York Times]] |access-date=28 November 2015 }}</ref>▼
|archive-date = 4 April 2023
|archive-url = https://web.archive.org/web/20230404081859/http://www.eolss.net/ebooklib/bookinfo/climate-change-human-systems-policy.aspx
|url-status = live
▲}}</ref> Other factors, including land use, [[ozone depletion]], animal husbandry ([[ruminant]] animals such as [[cattle]] produce [[methane]]<ref name="Steinfeld2006">{{cite book |
The [[US Geological Survey]] estimates are that volcanic emissions are at a much lower level than the effects of current human activities, which generate 100–300 times the amount of carbon dioxide emitted by volcanoes.<ref>{{cite web|url=http://volcanoes.usgs.gov/Hazards/What/VolGas/volgas.html|title=Volcanic Gases and Their Effects|date=10 January 2006|publisher=U.S. Department of the Interior|access-date=21 January 2008|archive-date=1 August 2013|archive-url=https://web.archive.org/web/20130801120440/http://volcanoes.usgs.govvolcanoes.usgs.gov/|url-status=live}}</ref> The annual amount put out by human activities may be greater than the amount released by [[Supervolcano|supereruptions]], the most recent of which was the [[Toba catastrophe theory|Toba eruption]] in Indonesia 74,000 years ago.<ref name="www.agu.org">{{cite web|url=http://www.agu.org/news/press/pr_archives/2011/2011-22.shtml|title=Human Activities Emit Way More Carbon Dioxide Than Do Volcanoes|date=14 June 2011|publisher=[[American Geophysical Union]]|access-date=20 June 2011|archive-date=9 May 2013|archive-url=https://web.archive.org/web/20130509191429/http://www.agu.org/news/press/pr_archives/2011/2011-22.shtml|url-status=dead}}</ref>
==== Orbital variations ====
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[[File:Solar Activity Proxies.png|thumb|right|upright=1.35|Variations in solar activity during the last several centuries based on observations of [[sunspot]]s and [[beryllium]] isotopes. The period of extraordinarily few sunspots in the late 17th century was the [[Maunder minimum]].|alt=]]The [[Sun]] is the predominant source of [[energy]] input to the Earth's [[climate system]]. Other sources include [[Geothermal energy|geothermal]] energy from the Earth's core, tidal energy from the Moon and heat from the decay of radioactive compounds. Both long term variations in solar intensity are known to affect global climate.{{Sfn|Rohli|Vega|2018|p=296}} [[Solar Variation|Solar output varies]] on shorter time scales, including the 11-year [[solar cycle]]<ref>{{cite journal|last1=Willson|first1=Richard C.|last2=Hudson|first2=Hugh S.|year=1991|title=The Sun's luminosity over a complete solar cycle|journal=Nature|volume=351|issue=6321|pages=42–44|bibcode=1991Natur.351...42W|doi=10.1038/351042a0|s2cid=4273483}}</ref> and longer-term [[modulation]]s.<ref>{{Cite journal|last1=Turner|first1=T. Edward|last2=Swindles|first2=Graeme T.|last3=Charman|first3=Dan J.|last4=Langdon|first4=Peter G.|last5=Morris|first5=Paul J.|last6=Booth|first6=Robert K.|last7=Parry|first7=Lauren E.|last8=Nichols|first8=Jonathan E.|date=5 April 2016|title=Solar cycles or random processes? Evaluating solar variability in Holocene climate records|journal=Scientific Reports|language=en|volume=6|issue=1|pages=23961|doi=10.1038/srep23961|pmid=27045989|issn=2045-2322|pmc=4820721}}</ref> Correlation between sunspots and climate and tenuous at best.{{Sfn|Rohli|Vega|2018|p=296}}
[[History of the Earth|Three to four billion years ago]], the Sun emitted only 75% as much power as it does today.<ref name="Ribas 2010">{{Cite conference |last=Ribas |first=Ignasi |conference=IAU Symposium 264 'Solar and Stellar Variability – Impact on Earth and Planets' |title=The Sun and stars as the primary energy input in planetary atmospheres |journal=Proceedings of the International Astronomical Union |volume=264 |pages=3–18 |date=February 2010 |doi=10.1017/S1743921309992298 |bibcode=2010IAUS..264....3R |arxiv=0911.4872}}</ref> If the atmospheric composition had been the same as today, liquid water should not have existed on the Earth's surface. However, there is evidence for the presence of water on the early Earth, in the [[Hadean]]<ref name="Marty, B. 2006 421">{{cite journal |doi=10.2138/rmg.2006.62.18 |title=Water in the Early Earth |year=2006 |author=Marty, B. |journal=Reviews in Mineralogy and Geochemistry |volume=62 |issue=1 |pages=421–450 |bibcode=2006RvMG...62..421M}}</ref><ref>{{cite journal |doi=10.1126/science.1110873 |title=Zircon Thermometer Reveals Minimum Melting Conditions on Earliest Earth |year=2005 |last1=Watson |first1=E.B. |journal=Science |volume=308 |issue=5723 |pages=841–44 |pmid=15879213 |last2=Harrison |first2=TM|s2cid=11114317 |bibcode=2005Sci...308..841W}}</ref> and [[Archean]]<ref>{{cite journal |doi=10.1130/0091-7613(1994)022<1067:SWIISL>2.3.CO;2 |title=Surface-water influx in shallow-level Archean lode-gold deposits in Western, Australia |year=1994 |last1=Hagemann |first1=Steffen G. |last2=Gebre-Mariam |first2=Musie |last3=Groves |first3=David I. |journal=Geology |volume=22 |issue=12 |page=1067 |bibcode=1994Geo....22.1067H}}</ref><ref name="Marty, B. 2006 421"/> eons, leading to what is known as the [[faint young Sun paradox]].<ref name="Sagan1972">{{cite journal | last = Sagan | first = C. | author2 = G. Mullen | title = Earth and Mars: Evolution of Atmospheres and Surface Temperatures | journal = Science | volume = 177 | issue = 4043 | pages = 52–6 | year = 1972 | url = http://www.sciencemag.org/cgi/content/abstract/177/4043/52?ck=nck | bibcode = 1972Sci...177...52S | doi = 10.1126/science.177.4043.52 | pmid = 17756316 | s2cid = 12566286 | access-date = 30 January 2009 | archive-date = 9 August 2010 | archive-url = https://web.archive.org/web/20100809113551/http://www.sciencemag.org/cgi/content/abstract/177/4043/52?ck=nck | url-status = live }}</ref> Hypothesized solutions to this paradox include a vastly different atmosphere, with much higher concentrations of greenhouse gases than currently exist.<ref>{{cite journal |doi=10.1126/science.276.5316.1217 |title=The Early Faint Sun Paradox: Organic Shielding of Ultraviolet-Labile Greenhouse Gases |year=1997 |last1=Sagan |first1=C. |journal=Science |volume=276 |issue=5316 |pages=1217–21 |pmid=11536805 |last2=Chyba |first2=C|bibcode = 1997Sci...276.1217S }}</ref> Over the following approximately 4 billion years, the energy output of the Sun increased. Over the next five billion years, the Sun's ultimate death as it becomes a [[red giant]] and then a [[white dwarf]] will have large effects on climate, with the red giant phase possibly ending any life on Earth that survives until that time.<ref name="MNRAS 386">{{citation |last1=Schröder |first1=K.-P. |last2=Connon Smith |first2=Robert |date=2008 |title=Distant future of the Sun and Earth revisited |journal=[[Monthly Notices of the Royal Astronomical Society]] |volume=386 |issue=1 |pages=155–63 |doi=10.1111/j.1365-2966.2008.13022.x |bibcode=2008MNRAS.386..155S |arxiv=0801.4031 |s2cid=10073988}}</ref>
==== Volcanism ====
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| publisher = USGS
| access-date = 31 July 2014
| archive-date = 29 July 2014
| archive-url = https://web.archive.org/web/20140729142333/http://volcanoes.usgs.gov/hazards/gas/climate.php
| url-status = live
}}</ref> On average, such eruptions occur several times per century, and cause cooling (by partially blocking the transmission of solar radiation to the Earth's surface) for a period of several years. Although volcanoes are technically part of the lithosphere, which itself is part of the climate system, the IPCC explicitly defines volcanism as an external forcing agent.<ref>[http://archive.ipcc.ch/publications_and_data/ar4/syr/en/annexes.html Annexes] {{Webarchive|url=https://web.archive.org/web/20190706041420/https://archive.ipcc.ch/publications_and_data/ar4/syr/en/annexes.html |date=6 July 2019 }}, in {{Harvnb|IPCC AR4 SYR|2008|p=58}}.</ref>
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|publisher=[[United States Geological Survey]]
|access-date=8 October 2009
|archive-date=25 August 2013
|archive-url=https://web.archive.org/web/20130825233934/http://pubs.usgs.gov/fs/1997/fs113-97/
|url-status=live
}}</ref><ref>{{cite web
| last1 = Diggles
| first1 = Michael | title = The Cataclysmic 1991 Eruption of Mount Pinatubo, Philippines
| url = http://pubs.usgs.gov/fs/1997/fs113-97/
| website = usgs.gov
| access-date = 31 July 2014
| archive-date = 25 August 2013
| archive-url = https://web.archive.org/web/20130825233934/http://pubs.usgs.gov/fs/1997/fs113-97/
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}}</ref> and the [[1815 eruption of Mount Tambora]] causing the [[Year Without a Summer]].<ref>{{cite journal
|doi=10.1191/0309133303pp379ra
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Over the course of millions of years, the motion of tectonic plates reconfigures global land and ocean areas and generates topography. This can affect both global and local patterns of climate and atmosphere-ocean circulation.<ref>{{Cite journal| year =1999| title = Paleoaltimetry incorporating atmospheric physics and botanical estimates of paleoclimate| journal = Geological Society of America Bulletin| volume = 111| pages = 497–511| issue = 4 | doi = 10.1130/0016-7606(1999)111<0497:PIAPAB>2.3.CO;2| first4 = K.A.| last2 = Wolfe | first1 = C.E.| last3 = Molnar | first2 = J.A.| first3 = P.| last4 = Emanuel| last1 = Forest|bibcode = 1999GSAB..111..497F | hdl = 1721.1/10809| hdl-access = free}}</ref>
The position of the continents determines the geometry of the oceans and therefore influences patterns of ocean circulation. The locations of the seas are important in controlling the transfer of heat and moisture across the globe, and therefore, in determining global climate. A recent example of tectonic control on ocean circulation is the formation of the [[Isthmus of Panama]] about 5 million years ago, which shut off direct mixing between the [[Atlantic]] and [[Pacific]] Oceans. This strongly affected the [[western boundary current|ocean dynamics]] of what is now the [[Gulf Stream]] and may have led to Northern Hemisphere ice cover.<ref>{{cite web|url=http://earthobservatory.nasa.gov/Newsroom/NewImages/images.php3?img_id=16401 |title=Panama: Isthmus that Changed the World |access-date=1 July 2008 |publisher=[[NASA]] Earth Observatory |url-status=dead |archive-url=https://web.archive.org/web/20070802015424/http://earthobservatory.nasa.gov/Newsroom/NewImages/images.php3?img_id=16401 |archive-date=2 August 2007 }}</ref><ref>{{cite journal |url=http://www.whoi.edu/oceanus/viewArticle.do?id=2508 |title=How the Isthmus of Panama Put Ice in the Arctic |first1=Gerald H. |last1=Haug |first2=Lloyd D. |last2=Keigwin |date=22 March 2004 |journal=Oceanus |volume=42 |issue=2 |publisher=[[Woods Hole Oceanographic Institution]] |access-date=1 October 2013 |archive-date=5 October 2018 |archive-url=https://web.archive.org/web/20181005081528/http://www.whoi.edu/oceanus/viewArticle.do?id=2508 |url-status=live }}</ref> During the [[Carboniferous]] period, about 300 to 360 million years ago, plate tectonics may have triggered large-scale storage of carbon and increased [[wikt:glaciation|glaciation]].<ref>{{cite journal|title=Isotope stratigraphy of the European Carboniferous: proxy signals for ocean chemistry, climate and tectonics|date=30 September 1999|volume=161|issue=1–3|doi=10.1016/S0009-2541(99)00084-4|pages=127–63|first1=Peter |last1=Bruckschen|first2=Susanne |last2=Oesmanna|first3=Ján |last3=Veizer |journal=Chemical Geology|bibcode=1999ChGeo.161..127B}}</ref> Geologic evidence points to a "megamonsoonal" circulation pattern during the time of the [[supercontinent]] [[Pangaea]], and climate modeling suggests that the existence of the supercontinent was conducive to the establishment of monsoons.<ref>{{cite journal|first=Judith T. |last=Parrish|title=Climate of the Supercontinent Pangea|journal=The Journal of Geology|year=1993|volume=101|pages=215–33 |doi=10.1086/648217|issue=2|publisher=The University of Chicago Press|jstor=30081148|bibcode = 1993JG....101..215P |s2cid=128757269}}</ref>
The size of continents is also important. Because of the stabilizing effect of the oceans on temperature, yearly temperature variations are generally lower in coastal areas than they are inland. A larger supercontinent will therefore have more area in which climate is strongly seasonal than will several smaller continents or [[island]]s.
==== Other mechanisms ====
It has been postulated that [[ion]]ized particles known as [[cosmic ray]]s could impact cloud cover and thereby the climate. As the sun shields the Earth from these particles, changes in solar activity were hypothesized to influence climate indirectly as well. To test the hypothesis, [[CERN]] designed the [[CLOUD experiment]], which showed the effect of cosmic rays is too weak to influence climate noticeably.<ref>{{Cite web|url=https://www.carbonbrief.org/why-the-sun-is-not-responsible-for-recent-climate-change|title=Explainer: Why the sun is not responsible for recent climate change|last=Hausfather|first=Zeke|date=18 August 2017|website=Carbon Brief|access-date=5 September 2019|archive-date=17 March 2023|archive-url=https://web.archive.org/web/20230317140828/https://www.carbonbrief.org/why-the-sun-is-not-responsible-for-recent-climate-change/|url-status=live}}</ref><ref>{{Cite journal|last=Pierce|first=J. R.|date=2017|title=Cosmic rays, aerosols, clouds, and climate: Recent findings from the CLOUD experiment|journal=Journal of Geophysical Research: Atmospheres|volume=122|issue=15|pages=8051–55|doi=10.1002/2017JD027475|bibcode=2017JGRD..122.8051P|s2cid=125580175 |issn=2169-8996}}</ref>
Evidence exists that the [[Chicxulub crater|Chicxulub asteroid impact]] some 66 million years ago had severely affected the Earth's climate. Large quantities of sulfate aerosols were kicked up into the atmosphere, decreasing global temperatures by up to 26 °C and producing sub-freezing temperatures for a period of 3–16 years. The recovery time for this event took more than 30 years.<ref name="Brugger 2017">{{citation
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| volume=19 | pages=17167 | date=April 2017 | bibcode=2017EGUGA..1917167B | postscript=. }}</ref> The large-scale use of [[nuclear weapon]]s has also been investigated for its impact on the climate. The hypothesis is that soot released by large-scale fires blocks a significant fraction of sunlight for as much as a year, leading to a sharp drop in temperatures for a few years. This possible event is described as [[nuclear winter]].{{sfn|Burroughs|2001|p=232}}
[[Land surface effects on climate|Humans' use of land]] impact how much sunlight the surface reflects and the concentration of dust. Cloud formation is not only influenced by how much water is in the air and the temperature, but also by the amount of [[aerosols]] in the air such as dust.<ref>{{Cite web|url=https://www.chemistryworld.com/news/mineral-dust-plays-key-role-in-cloud-formation-and-chemistry/6157.article|title=Mineral dust plays key role in cloud formation and chemistry|last=Hadlington|first=Simon 9|date=May 2013|website=Chemistry World|access-date=5 September 2019|archive-date=24 October 2022|archive-url=https://web.archive.org/web/20221024053651/https://www.chemistryworld.com/news/mineral-dust-plays-key-role-in-cloud-formation-and-chemistry/6157.article|url-status=live}}</ref> Globally, more dust is available if there are many regions with dry soils, little vegetation and strong winds.<ref>{{Cite journal|last1=Mahowald|first1=Natalie|author-link=Natalie Mahowald|last2=Albani|first2=Samuel|last3=Kok|first3=Jasper F.|last4=Engelstaeder|first4=Sebastian|last5=Scanza|first5=Rachel|last6=Ward|first6=Daniel S.|last7=Flanner|first7=Mark G.|date=1 December 2014|title=The size distribution of desert dust aerosols and its impact on the Earth system|journal=Aeolian Research|volume=15|pages=53–71|bibcode=2014AeoRe..15...53M|doi=10.1016/j.aeolia.2013.09.002|issn=1875-9637|doi-access=free}}</ref>
== Evidence and measurement of climate changes ==
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==== Vegetation ====
A change in the type, distribution and coverage of vegetation may occur given a change in the climate. Some changes in climate may result in increased precipitation and warmth, resulting in improved plant growth and the subsequent sequestration of airborne CO<sub>2</sub>. The effects are expected to affect the rate of many natural cycles like [[plant litter]] decomposition rates.<ref>{{cite journal |last1=Ochoa-Hueso |first1=R |last2=Delgado-Baquerizo |first2=N |last3=King |first3=PTA |last4=Benham |first4=M |last5=Arca |first5=V |last6=Power |first6=SA |title=Ecosystem type and resource quality are more important than global change drivers in regulating early stages of litter decomposition |journal=Soil Biology and Biochemistry |date=2019 |volume=129 |pages=144–52 |doi=10.1016/j.soilbio.2018.11.009 |s2cid=92606851 }}</ref> A gradual increase in warmth in a region will lead to earlier flowering and fruiting times, driving a change in the timing of life cycles of dependent organisms. Conversely, cold will cause plant bio-cycles to lag.<ref>{{cite web |last=Kinver |first=Mark |date=15 November 2011 |title=UK trees' fruit ripening '18 days earlier' |publisher=Bbc.co.uk |url=https://www.bbc.co.uk/news/science-environment-15721263 |access-date=1 November 2012 |archive-date=17 March 2023 |archive-url=https://web.archive.org/web/20230317140816/https://www.bbc.co.uk/news/science-environment-15721263 |url-status=live }}</ref>
Larger, faster or more radical changes, however, may result in vegetation stress, rapid plant loss and [[desertification]] in certain circumstances.<ref name="SahneyBentonFalconLang 2010RainforestCollapse">{{cite journal |last1=Sahney |first1=S. |last2=Benton |first2=M.J. |last3=Falcon-Lang |first3=H.J. |year=2010 |title=Rainforest collapse triggered Pennsylvanian tetrapod diversification in Euramerica |journal=Geology |doi=10.1130/G31182.1 |bibcode=2010Geo....38.1079S |volume=38 |issue=12 |pages=1079–82 |url=https://www.academia.edu/368820 |format=PDF |access-date=27 November 2013 |archive-date=17 March 2023 |archive-url=https://web.archive.org/web/20230317140814/https://www.academia.edu/368820 |url-status=live }}</ref><ref>{{cite journal |last1=Bachelet |first1=D. |author-link1=Dominique Bachelet|last2=Neilson |first2=R. |last3=Lenihan |first3=J. M. |last4=Drapek |first4=R.J. |year=2001 |title=Climate Change Effects on Vegetation Distribution and Carbon Budget in the United States |journal=[[Ecosystems]] |doi=10.1007/s10021-001-0002-7 |volume=4 |issue=3 |pages=164–85 |s2cid=15526358 }}</ref> An example of this occurred during the [[Carboniferous Rainforest Collapse]] (CRC), an extinction event 300 million years ago. At this time vast rainforests covered the equatorial region of Europe and America. Climate change devastated these tropical rainforests, abruptly fragmenting the habitat into isolated 'islands' and causing the extinction of many plant and animal species.<ref name="SahneyBentonFalconLang 2010RainforestCollapse" />
==== Wildlife ====
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=== Paleo-Eocene Thermal maximum ===
[[File:65 Myr Climate Change.png|thumb|upright=1.35|right|Climate changes over the past 65 million years, using proxy data including [[Oxygen-18]] ratios from [[foraminifera]].]]
The [[Paleocene–Eocene Thermal Maximum]] (PETM) was a time period with more than 5–8 °C global average temperature rise across the event.<ref name="McInerney20112">{{cite journal|author=McInherney, F.A..|author2=Wing, S.|year=2011|title=A perturbation of carbon cycle, climate, and biosphere with implications for the future|url=http://www.whoi.edu/fileserver.do?id=136084&pt=2&p=148709|journal=Annual Review of Earth and Planetary Sciences|volume=39|pages=489–516|bibcode=2011AREPS..39..489M|doi=10.1146/annurev-earth-040610-133431|access-date=26 October 2019|archive-date=14 September 2016|archive-url=https://web.archive.org/web/20160914003526/http://www.whoi.edu/fileserver.do?id=136084&pt=2&p=148709|url-status=live}}</ref> This climate event occurred at the time boundary of the [[Paleocene]] and [[Eocene]] geological [[Epoch (geology)|epochs]].<ref name="Westerhold2008">{{cite journal|author=Westerhold, T..|author2=Röhl, U.|author3=Raffi, I.|author4=Fornaciari, E.|author5=Monechi, S.|author6=Reale, V.|author7=Bowles, J.|author8=Evans, H. F.|year=2008|title=Astronomical calibration of the Paleocene time|url=https://www.geo.arizona.edu/~reiners/fortransfer6/WesterholdEtAl_PPP2008.pdf |archive-url=https://web.archive.org/web/20170809094938/http://www.geo.arizona.edu/~reiners/fortransfer6/WesterholdEtAl_PPP2008.pdf |archive-date=2017-08-09 |url-status=live|journal=Palaeogeography, Palaeoclimatology, Palaeoecology|volume=257|issue=4|pages=377–403|bibcode=2008PPP...257..377W|doi=10.1016/j.palaeo.2007.09.016}}</ref> During the event large amounts of [[methane]] was released, a potent greenhouse gas.{{Sfn|Burroughs|2007|p=|pp=190–91}} The PETM represents a "case study" for modern climate change as in the greenhouse gases were released in a geologically relatively short amount of time.<ref name="McInerney20112"/> During the PETM, a mass extinction of organisms in the deep ocean took place.<ref>{{Cite journal|last1=Ivany|first1=Linda C.|last2=Pietsch|first2=Carlie|last3=Handley|first3=John C.|last4=Lockwood|first4=Rowan|last5=Allmon|first5=Warren D.|last6=Sessa|first6=Jocelyn A.|date=1 September 2018|title=Little lasting impact of the Paleocene-Eocene Thermal Maximum on shallow marine molluscan faunas|journal=Science Advances|language=en|volume=4|issue=9|pages=eaat5528|doi=10.1126/sciadv.aat5528|issn=2375-2548|pmid=30191179|pmc=6124918|bibcode=2018SciA....4.5528I}}</ref>
=== The Cenozoic ===
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{{main|Climate change}}
As a consequence of humans emitting [[greenhouse gas]]es, [[Surface air temperature|global surface temperatures]] have started rising. Global warming is an aspect of modern climate change, a term that also includes the observed changes in precipitation, storm tracks and cloudiness. As a consequence, glaciers worldwide have been found to be [[The Retreat of Glaciers Since 1850|shrinking significantly]].<ref name="Zemp2008">{{cite report|url=http://www.grid.unep.ch/glaciers/pdfs/summary.pdf|title=United Nations Environment Programme – Global Glacier Changes: facts and figures|last=Zemp|first=M.|author2=I.Roer|author3=A.Kääb|author4=M.Hoelzle|author5=F.Paul|author6=W. Haeberli|access-date=21 June 2009|archive-url=https://web.archive.org/web/20090325100332/http://www.grid.unep.ch/glaciers/pdfs/summary.pdf|year=2008|archive-date=25 March 2009|url-status=dead}}</ref><ref name="EPAGlacialBalance">{{cite web|url=https://www.epa.gov/climate-indicators/climate-change-indicators-glaciers|title=Climate Change Indicators: Glaciers|last=EPA, OA|first=US|website=US EPA|date=July 2016|access-date=26 January 2018|archive-date=29 September 2019|archive-url=https://web.archive.org/web/20190929003522/https://www.epa.gov/climate-indicators/climate-change-indicators-glaciers|url-status=live}}</ref> Land ice sheets in both [[Antarctica]] and [[Greenland]] have been losing mass since 2002 and have seen an acceleration of ice mass loss since 2009.<ref>{{cite web|url=https://climate.nasa.gov/vital-signs/land-ice/|title=Land ice – NASA Global Climate Change|access-date=10 December 2017|archive-date=23 February 2017|archive-url=https://web.archive.org/web/20170223211832/https://climate.nasa.gov/vital-signs/land-ice/|url-status=live}}</ref> Global sea levels have been rising as a consequence of thermal expansion and ice melt. The decline in Arctic sea ice, both in extent and thickness, over the last several decades is further evidence for rapid climate change.<ref>{{cite web|url=https://climate.nasa.gov/evidence/|title=Climate Change: How do we know?|editor1-last=Shaftel|editor1-first=Holly|website=NASA Global Climate Change|publisher=Earth Science Communications Team at NASA's Jet Propulsion Laboratory|access-date=16 December 2017|archive-date=18 December 2019|archive-url=https://web.archive.org/web/20191218104252/https://climate.nasa.gov/evidence/|url-status=live}}</ref>
==== Variability between regions {{anchor|Contemporaneous regional variability}} ====
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