Editing Climate variability and change (section)

=== 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>