Editing Climate variability and change (section)

==== 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 }}</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>