Editing Causes of climate change (section)

== Natural variability ==
{{Further|Climate variability and change|Solar activity and climate}}
{{See also|Climate change denial|History of climate change science#Discredited theories and reconciled apparent discrepancies}}
[[File:2017 Global warming attribution - based on NCA4 Fig 3.3 - single-panel version.svg|thumb|right| The [[Fourth National Climate Assessment]] ("NCA4", USGCRP, 2017) includes charts illustrating that neither solar nor volcanic activity can explain the observed warming.<ref>{{cite journal |title=Climate Science Special Report: Fourth National Climate Assessment, Volume I - Chapter 3: Detection and Attribution of Climate Change |url=https://science2017.globalchange.gov/chapter/3/ |website=science2017.globalchange.gov |publisher=U.S. Global Change Research Program (USGCRP) |archive-url=https://web.archive.org/web/20190923190450/https://science2017.globalchange.gov/chapter/3/ |archive-date=23 September 2019 |date=2017 |pages=1–470 |url-status=live}} Adapted directly from Fig. 3.3.</ref><ref>{{cite journal |title=Climate Science Special Report / Fourth National Climate Assessment (NCA4), Volume I /Executive Summary / Highlights of the Findings of the U.S. Global Change Research Program Climate Science Special Report |url=https://science2017.globalchange.gov/chapter/executive-summary/ |website=globalchange.gov |publisher=U.S. Global Change Research Program |archive-url=https://web.archive.org/web/20190614150544/https://science2017.globalchange.gov/chapter/executive-summary/ |archive-date=14 June 2019 |date=23 November 2018 |doi=10.7930/J0DJ5CTG |url-status=live |last1=Wuebbles |first1=D.J. |last2=Fahey |first2=D.W. |last3=Hibbard |first3=K.A. |last4=Deangelo |first4=B. |last5=Doherty |first5=S. |last6=Hayhoe |first6=K. |last7=Horton |first7=R. |last8=Kossin |first8=J.P. |last9=Taylor |first9=P.C. |last10=Waple |first10=A.M. |last11=Yohe |first11=C.P. |pages=1–470 |doi-access=free}}</ref>]]
Already in 2001, the [[IPCC Third Assessment Report]] had found that, "The combined change in radiative forcing of the two major natural factors (solar variation and volcanic aerosols) is estimated to be negative for the past two, and possibly the past four, decades."<ref>IPCC (2001) [https://www.ipcc.ch/site/assets/uploads/2018/07/WG1_TAR_SPM.pdf Summary for Policymakers] - A Report of Working Group I of the Intergovernmental Panel on Climate Change. In: [https://www.ipcc.ch/report/ar3/wg1/ TAR Climate Change 2001: The Scientific Basis]</ref> [[solar variation|Solar irradiance]] has been measured directly by [[satellite]]s,<ref>{{Harvnb|National Academies|2008|p=6}}</ref> and indirect measurements are available from the early 1600s onwards.<ref name="NCAR4_ch2" /> Yet, since 1880, there has been no upward trend in the amount of the Sun's energy reaching the Earth, in contrast to the warming of the lower atmosphere (the [[troposphere]]).<ref>{{cite web|title=Is the Sun causing global warming?|website=Climate Change: Vital Signs of the Planet|url=https://climate.nasa.gov/faq/14/is-the-sun-causing-global-warming|access-date=10 May 2019|archive-url=https://web.archive.org/web/20190505160051/https://climate.nasa.gov/faq/14/is-the-sun-causing-global-warming/|archive-date=5 May 2019|url-status=live}}</ref> Similarly, volcanic activity has the single largest natural impact (forcing) on temperature, yet it is equivalent to less than 1% of current human-caused CO<sub>2</sub> emissions.<ref>{{Cite journal |last1=Fischer |first1=Tobias P. |last2=Aiuppa |first2=Alessandro |date=2020 |title=AGU Centennial Grand Challenge: Volcanoes and Deep Carbon Global CO 2 Emissions From Subaerial Volcanism—Recent Progress and Future Challenges |url=https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2019GC008690 |journal=Geochemistry, Geophysics, Geosystems |language=en |volume=21 |issue=3 |doi=10.1029/2019GC008690 |issn=1525-2027|hdl=10447/498846 |hdl-access=free }}</ref> Volcanic activity as a whole has had negligible impacts on global temperature trends since the Industrial Revolution.<ref name="USGCRP Chapter 2 2017 79">{{harvnb|USGCRP Chapter 2|2017|p=79}}</ref>

Between 1750 and 2007, solar radiation may have at most increased by 0.12&nbsp;W/m<sup>2</sup>, compared to 1.6&nbsp;W/m<sup>2</sup> for the net anthropogenic forcing.<ref>IPCC, 2007: [https://www.ipcc.ch/site/assets/uploads/2018/02/ar4-wg1-spm-1.pdf Summary for Policymakers]. In: [https://www.ipcc.ch/site/assets/uploads/2018/02/ar4-wg1-spm-1.pdf Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change] [Solomon, S., D. Qin, M. Manning, Z. Chen, M. Marquis, K.B. Averyt, M.Tignor and H.L. Miller (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA.</ref>{{rp|3}}  Consequently, the observed rapid rise in global mean temperatures seen after 1985 cannot be ascribed to [[solar activity|solar variability]]."<ref name=":02">{{cite journal |last1=Lockwood |first1=Mike |last2=Lockwood |first2=Claus |year=2007 |title=Recent oppositely directed trends in solar climate forcings and the global mean surface air temperature |url=http://www.pubs.royalsoc.ac.uk/media/proceedings_a/rspa20071880.pdf |journal=Proceedings of the Royal Society A |volume=463 |issue=2086 |pages=2447–2460 |bibcode=2007RSPSA.463.2447L |doi=10.1098/rspa.2007.1880 |s2cid=14580351 |archive-url=https://web.archive.org/web/20070926023811/http://www.pubs.royalsoc.ac.uk/media/proceedings_a/rspa20071880.pdf |archive-date=26 September 2007 |access-date=21 July 2007}}</ref> Further, the upper atmosphere (the [[stratosphere]]) would also be warming if the Sun was sending more energy to Earth, but instead, it has been cooling.<ref name="USGCRP-2009">{{Harvnb|USGCRP|2009|p=20}}.</ref> This is consistent with greenhouse gases preventing heat from leaving the Earth's atmosphere.<ref>{{Harvnb|IPCC AR4 WG1 Ch9|2007|pp=702–703}}; {{harvnb|Randel|Shine|Austin|Barnett|2009}}.</ref> 
 
[[Types of volcanic eruptions#Plinian|Explosive volcanic eruptions]] can release gases, dust and ash that partially block sunlight and reduce temperatures, or they can send water vapor into the atmosphere, which adds to greenhouse gases and increases temperatures.<ref>{{cite web |url=https://climate.nasa.gov/news/3204/tonga-eruption-blasted-unprecedented-amount-of-water-into-stratosphere/ |title=Tonga eruption blasted unprecedented amount of water into stratosphere |last=Greicius |first=Tony |date=2022-08-02 |website=NASA Global Climate Change |access-date=2024-01-18 |quote=Massive volcanic eruptions like Krakatoa and Mount Pinatubo typically cool Earth’s surface by ejecting gases, dust, and ash that reflect sunlight back into space. In contrast, the Tonga volcano didn’t inject large amounts of aerosols into the stratosphere, and the huge amounts of water vapor from the eruption may have a small, temporary warming effect, since water vapor traps heat. The effect would dissipate when the extra water vapor cycles out of the stratosphere and would not be enough to noticeably exacerbate climate change effects.}}</ref> Because both water vapor and volcanic material have low persistence in the atmosphere, even the largest eruptions only have an effect for several years.<ref name="USGCRP Chapter 2 2017 79"/>