Editing Climate variability and change (section)

== Causes ==

On the broadest scale, the rate at which energy is received from the [[Sun]] and the rate at which it is lost to space determine the [[equilibrium temperature]] and climate of Earth. This energy is distributed around the globe by winds, ocean currents,<ref name="Hsiung-1985">{{cite journal | title=Estimates of Global Oceanic Meridional Heat Transport | first1=Jane | last1=Hsiung | journal=Journal of Physical Oceanography | volume=15 | issue=11 | pages=1405–13 | date=November 1985 | doi=10.1175/1520-0485(1985)015<1405:EOGOMH>2.0.CO;2 | bibcode=1985JPO....15.1405H | doi-access=free }}</ref><ref name="Vallis-2009">{{cite journal | title=Meridional energy transport in the coupled atmosphere–ocean system: scaling and numerical experiments | first1=Geoffrey K. | last1=Vallis | first2=Riccardo | last2=Farneti | s2cid=122384001 | volume=135 | issue=644 | date=October 2009 | pages=1643–60 | journal=Quarterly Journal of the Royal Meteorological Society | doi=10.1002/qj.498 | bibcode=2009QJRMS.135.1643V }}</ref> and other mechanisms to affect the climates of different regions.<ref name="Trenberth-2009">{{cite journal | title=Earth's Global Energy Budget | last1=Trenberth | first1=Kevin E. | last2=Fasullo | first2=John T. | last3=Kiehl | first3=Jeffrey | display-authors=1 | journal=Bulletin of the American Meteorological Society | volume=90 | issue=3 | pages=311–23 | year=2009 | doi=10.1175/2008BAMS2634.1 | bibcode=2009BAMS...90..311T | doi-access=free }}</ref>

Factors that can shape climate are called [[climate forcing]]s or "forcing mechanisms".<ref name="Smith-2013">{{cite book |last=Smith |first=Ralph C. |year=2013 |title=Uncertainty Quantification: Theory, Implementation, and Applications |series=Computational Science and Engineering |publisher=SIAM |isbn=978-1611973228 |volume=12 |page=23 |url=https://books.google.com/books?id=Tc1GAgAAQBAJ&pg=PA23}}</ref> These include processes such as variations in [[solar radiation]], variations in the Earth's orbit, variations in the [[albedo]] or reflectivity of the continents, atmosphere, and oceans, [[orogeny|mountain-building]] and [[continental drift]] and changes in [[greenhouse gas]] concentrations. External forcing can be either anthropogenic (e.g. increased emissions of greenhouse gases and dust) or natural (e.g., changes in solar output, the Earth's orbit, volcano eruptions).<ref>{{harvnb|Cronin|2010|pp=17–18}}</ref> There are a variety of [[climate change feedback]]s that can either amplify or diminish the initial forcing. There are also key [[Tipping points in the climate system|thresholds]] which when exceeded can produce rapid or irreversible change.

Some parts of the climate system, such as the oceans and ice caps, respond more slowly in reaction to climate forcings, while others respond more quickly. An example of fast change is the atmospheric cooling after a volcanic eruption, when [[volcanic ash]] reflects sunlight. [[Thermal expansion]] of ocean water after atmospheric warming is slow, and can take thousands of years. A combination is also possible, e.g., sudden loss of [[albedo]] in the Arctic Ocean as sea ice melts, followed by more gradual thermal expansion of the water.

Climate variability can also occur due to internal processes. Internal unforced processes often involve changes in the distribution of energy in the ocean and atmosphere, for instance, changes in the [[thermohaline circulation]].

=== 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>

=== External climate forcing ===

==== Greenhouse gases ====
{{Main|Greenhouse gas}}
[[File:Carbon Dioxide 800kyr.svg|thumb|right|upright=1.35|{{CO2}} concentrations over the last 800,000 years as measured from ice cores (blue/green) and directly (black)]]
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=Australian Academy of Science |website=science.org.au |access-date=12 August 2017 |archive-date=8 May 2019 |archive-url=https://web.archive.org/web/20190508094624/https://www.science.org.au/learning/general-audience/science-booklets-0/science-climate-change/3-are-human-activities-causing |url-status=live }}</ref> release of trace gases (e.g. nitrogen oxides, carbon monoxide, or methane).<ref>{{cite book
 |title        = Climate Change, Human Systems and Policy Volume I
 |chapter      = Anthropogenic Climate Influences
 |editor       = Antoaneta Yotova
 |date         = 2009
 |publisher    = Eolss Publishers
 |isbn         = 978-1-905839-02-5
 |url          = https://www.eolss.net/ebooklib/bookinfo/climate-change-human-systems-policy.aspx
 |access-date  = 16 August 2020
 |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="Steinfeld-2006">{{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 |access-date=21 July 2009 |archive-date=26 July 2008 |archive-url=https://web.archive.org/web/20080726214204/http://www.fao.org/docrep/010/a0701e/a0701e00.htm |url-status=live }}</ref>), and [[deforestation]], also play a role.<ref name="NYT-2015">{{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 |archive-date=29 November 2015 |archive-url=https://web.archive.org/web/20151129034132/http://www.nytimes.com/2015/11/29/opinion/sunday/what-the-paris-climate-meeting-must-do.html |url-status=live }}</ref>

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="AGU-2011">{{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 ====
[[File:MilankovitchCyclesOrbitandCores.png|thumb|left|upright=1.35|Milankovitch cycles from 800,000 years ago in the past to 800,000 years in the future.]]
Slight variations in Earth's motion lead to changes in the seasonal distribution of sunlight reaching the Earth's surface and how it is distributed across the globe. There is very little change to the area-averaged annually averaged sunshine; but there can be strong changes in the geographical and seasonal distribution. The three types of [[Kinematics|kinematic]] change are variations in Earth's [[Orbital eccentricity|eccentricity]], changes in [[axial tilt|the tilt angle of Earth's axis of rotation]], and [[precession]] of Earth's axis. Combined, these produce [[Milankovitch cycles]] which affect climate and are notable for their correlation to [[glacial period|glacial]] and [[interglacial period]]s,<ref name="UniMontana">{{cite web |url=http://www.homepage.montana.edu/~geol445/hyperglac/time1/milankov.htm|archive-url=https://web.archive.org/web/20110716144130/http://www.homepage.montana.edu/~geol445/hyperglac/time1/milankov.htm|archive-date=16 July 2011|title= Milankovitch Cycles and Glaciation|access-date=2 April 2009 |publisher= University of Montana}}</ref> their correlation with the advance and retreat of the [[Sahara]],<ref name="UniMontana"/> and for their [[cyclostratigraphy|appearance]] in the [[geologic record|stratigraphic record]].<ref>{{cite journal |doi=10.1111/j.1365-3121.1989.tb00403.x|title=A Milankovitch scale for Cenomanian time|year=1989|author=Gale, Andrew S. |journal=Terra Nova |volume=1|pages=420–25|issue=5|bibcode=1989TeNov...1..420G}}</ref><ref>{{cite web|title=Same forces as today caused climate changes 1.4 billion years ago|url=http://www.sdu.dk/en/Om_SDU/Fakulteterne/Naturvidenskab/Nyheder/2015_03_10_climate_cycles|website=sdu.dk|publisher=University of Denmark.|url-status=dead|archive-url=https://web.archive.org/web/20150312163250/http://www.sdu.dk/en/Om_SDU/Fakulteterne/Naturvidenskab/Nyheder/2015_03_10_climate_cycles|archive-date=12 March 2015}}</ref>

During the glacial cycles, there was a high correlation between {{CO2}} concentrations and temperatures. Early studies indicated that {{CO2}} concentrations lagged temperatures, but it has become clear that this is not always the case.<ref name="van Nes-2015">{{Cite journal|last1=van Nes|first1=Egbert H.|last2=Scheffer|first2=Marten|last3=Brovkin|first3=Victor|last4=Lenton|first4=Timothy M.|last5=Ye|first5=Hao|last6=Deyle|first6=Ethan|last7=Sugihara|first7=George|date=2015|title=Causal feedbacks in climate change|journal=Nature Climate Change|language=en|volume=5|issue=5|pages=445–48|doi=10.1038/nclimate2568|bibcode=2015NatCC...5..445V|issn=1758-6798}}</ref> When ocean temperatures increase, the [[solubility]] of {{CO2}} decreases so that it is released from the ocean. The exchange of {{CO2}} between the air and the ocean can also be impacted by further aspects of climatic change.<ref>[http://archive.ipcc.ch/publications_and_data/ar4/wg1/en/ch6s6-4.html Box 6.2: What Caused the Low Atmospheric Carbon Dioxide Concentrations During Glacial Times?] {{Webarchive|url=https://web.archive.org/web/20230108231413/https://archive.ipcc.ch/publications_and_data/ar4/wg1/en/ch6s6-4.html |date=8 January 2023 }} in {{Harvnb|IPCC AR4 WG1|2007}} .</ref> These and other self-reinforcing processes allow small changes in Earth's motion to have a large effect on climate.<ref name="van Nes-2015" />

==== Solar output ====
[[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-2006">{{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-2006"/> eons, leading to what is known as the [[faint young Sun paradox]].<ref name="Sagan-1972">{{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 | url-access = subscription }}</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="Schröder-2008">{{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 |doi-access=free |bibcode=2008MNRAS.386..155S |arxiv=0801.4031 |s2cid=10073988}}</ref>

==== Volcanism ====
[[File:Msu 1978-2010.jpg|thumb|left|upright=1.35|In atmospheric temperature from 1979 to 2010, determined by [[Microwave sounding unit|MSU]] [[NASA]] satellites, effects appear from [[aerosols]] released by major volcanic eruptions ([[El&nbsp;Chichón]] and [[Mount Pinatubo|Pinatubo]]). [[El Niño-Southern Oscillation|El&nbsp;Niño]] is a separate event, from ocean variability.]]
The [[Volcano|volcanic eruptions]] considered to be large enough to affect the Earth's climate on a scale of more than 1 year are the ones that inject over 100,000 [[ton]]s of [[sulfur dioxide|SO<sub>2</sub>]] into the [[stratosphere]].<ref name="Miles-2004">{{cite journal
| last1 = Miles | first1 = M.G.
| last2 = Grainger | first2 = R.G.
| last3 = Highwood | first3 = E.J.
| title = The significance of volcanic eruption strength and frequency for climate
| journal = Quarterly Journal of the Royal Meteorological Society
| date = 2004
| volume = 130 | pages = 2361–76
| issue = 602
| doi = 10.1256/qj.03.60
| bibcode = 2004QJRMS.130.2361M
| s2cid = 53005926
}}</ref> This is due to the optical properties of SO<sub>2</sub> and sulfate aerosols, which strongly absorb or scatter solar radiation, creating a global layer of [[sulfuric acid]] haze.<ref>{{cite web
| title = Volcanic Gases and Climate Change Overview
| url = http://volcanoes.usgs.gov/hazards/gas/climate.php
| website = usgs.gov
| 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>

Notable eruptions in the historical records are the [[1991 eruption of Mount Pinatubo]] which lowered global temperatures by about 0.5&nbsp;°C (0.9&nbsp;°F) for up to three years,<ref>{{cite web
|url=http://pubs.usgs.gov/fs/1997/fs113-97/
|title=The Cataclysmic 1991 Eruption of Mount Pinatubo, Philippines
|last=Diggles
|first=Michael
|date=28 February 2005
|work=U.S. Geological Survey Fact Sheet 113-97
|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/
| url-status = live
}}</ref> and the [[1815 eruption of Mount Tambora]] causing the [[Year Without a Summer]].<ref>{{cite journal
|doi=10.1191/0309133303pp379ra
|title=Climatic, environmental and human consequences of the largest known historic eruption: Tambora volcano (Indonesia) 1815
|year=2003
|last1=Oppenheimer|first1=Clive
|journal=Progress in Physical Geography
|volume=27
|pages=230–59
|issue=2
|bibcode=2003PrPG...27..230O
|s2cid=131663534
}}</ref>

At a larger scale—a few times every 50 million to 100 million years—the eruption of [[large igneous province]]s brings large quantities of [[igneous rock]] from the [[mantle (geology)|mantle]] and [[lithosphere]] to the Earth's surface. Carbon dioxide in the rock is then released into the atmosphere.<ref>{{Cite journal|title=Deep Carbon and the Life Cycle of Large Igneous Provinces|last1=Black|first1=Benjamin A.|last2=Gibson|first2=Sally A.|date=2019|journal=Elements|doi=10.2138/gselements.15.5.319|volume=15|issue=5|pages=319–324|doi-access=free|bibcode=2019Eleme..15..319B }}</ref>
<ref>{{cite journal
|doi=10.1016/S0012-8252(00)00037-4
|title=Large igneous provinces and mass extinctions
|year=2001
|last1=Wignall|first1=P
|journal=Earth-Science Reviews
|volume=53
|issue=1
|pages=1–33
|bibcode=2001ESRv...53....1W
}}</ref> Small eruptions, with injections of less than 0.1&nbsp;Mt of sulfur dioxide into the stratosphere, affect the atmosphere only subtly, as temperature changes are comparable with natural variability. However, because smaller eruptions occur at a much higher frequency, they too significantly affect Earth's atmosphere.<ref name="Miles-2004" /><ref name="Graf-1997">{{cite journal
| last1 = Graf | first1 = H.-F.
| last2 = Feichter | first2 = J.
| last3 = Langmann | first3 = B.
| title = Volcanic sulphur emissions: Estimates of source strength and its contribution to the global sulphate distribution
| journal = Journal of Geophysical Research: Atmospheres
| date = 1997
| volume = 102 | issue = D9
| pages = 10727–38
| doi = 10.1029/96JD03265
| bibcode=1997JGR...10210727G
| hdl = 21.11116/0000-0003-2CBB-A
| hdl-access = free
}}</ref>

==== Plate tectonics ====
{{Main|Plate tectonics}}
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&nbsp;°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
 | contribution=Severe environmental effects of Chicxulub impact imply key role in end-Cretaceous mass extinction
 | last1=Brugger | first1=Julia
 | last2=Feulner | first2=Georg | last3=Petri | first3=Stefan
 | title=19th EGU General Assembly, EGU2017, proceedings from the conference, 23–28 April 2017|location=Vienna, Austria
 | 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>