Causes of climate change

Drivers of climate change from 1850–1900 to 2010–2019. Future global warming potential for long lived drivers like carbon dioxide emissions is not represented.

The scientific community has been investigating the causes of climate change for decades. After thousands of studies, it came to a consensus, where it is "unequivocal that human influence has warmed the atmosphere, ocean and land since pre-industrial times."[1]: 3  This consensus is supported by around 200 scientific organizations worldwide,[2] The dominant role in this climate change has been played by the direct emissions of carbon dioxide from the burning of fossil fuels. Indirect CO2 emissions from land use change, and the emissions of methane, nitrous oxide and other greenhouse gases play major supporting roles.[1]

Observed temperature from NASA[3] vs the 1850–1900 average used by the IPCC as a pre-industrial baseline.[4] The primary driver for increased global temperatures in the industrial era is human activity, with natural forces adding variability.[5]

The warming from the greenhouse effect has a logarithmic relationship with the concentration of greenhouse gases. This means that every additional fraction of CO2 and the other greenhouse gases in the atmosphere has a slightly smaller warming effect than the fractions before it as the total concentration increases. However, only around half of CO2 emissions continually reside in the atmosphere in the first place, as the other half is quickly absorbed by carbon sinks in the land and oceans.[6]: 450  Further, the warming per unit of greenhouse gases is also affected by feedbacks, such as the changes in water vapor concentrations or Earth's albedo (reflectivity).[7]: 2233 

As the warming from CO2 increases, carbon sinks absorb a smaller fraction of total emissions, while the "fast" climate change feedbacks amplify greenhouse gas warming. Thus, both effects are considered to each other out, and the warming from each unit of CO2 emitted by humans increases temperature in linear proportion to the total amount of emissions.[8]: 746  Further, some fraction of the greenhouse warming has been "masked" by the human-caused emissions of sulfur dioxide, which forms aerosols that have a cooling effect. However, this masking has been receding in the recent years, due to measures to combat acid rain and air pollution caused by sulfates.[9][10]

  1. ^ a b Eyring, Veronika; Gillett, Nathan P.; Achutarao, Krishna M.; Barimalala, Rondrotiana; et al. (2021). "Chapter 3: Human influence on the climate system" (PDF). IPCC AR6 WG1 2021.
  2. ^ OPR (n.d.), Office of Planning and Research (OPR) List of Organizations, OPR, Office of the Governor, State of California, archived from the original on 1 April 2014, retrieved 30 November 2013. Archived page: The source appears to incorrectly list the Society of Biology (UK) twice.
  3. ^ "Global Annual Mean Surface Air Temperature Change". NASA. Archived from the original on 16 April 2020. Retrieved 23 February 2020..
  4. ^ IPCC AR5 SYR Glossary 2014, p. 124.
  5. ^ USGCRP Chapter 3 2017 Figure 3.1 panel 2 Archived 9 April 2018 at the Wayback Machine, Figure 3.3 panel 5 .
  6. ^ Bindoff, N.L., W.W.L. Cheung, J.G. Kairo, J. Arístegui, V.A. Guinder, R. Hallberg, N. Hilmi, N. Jiao, M.S. Karim, L. Levin, S. O’Donoghue, S.R. Purca Cuicapusa, B. Rinkevich, T. Suga, A. Tagliabue, and P. Williamson, 2019: Chapter 5: Changing Ocean, Marine Ecosystems, and Dependent Communities. In: IPCC Special Report on the Ocean and Cryosphere in a Changing Climate [H.-O. Pörtner, D.C. Roberts, V. Masson-Delmotte, P. Zhai, M. Tignor, E. Poloczanska, K. Mintenbeck, A. Alegría, M. Nicolai, A. Okem, J. Petzold, B. Rama, N.M. Weyer (eds.)]. Cambridge University Press, Cambridge, UK and New York, NY, USA, pp. 447–587. https://doi.org/10.1017/9781009157964.007.
  7. ^ IPCC, 2021: Annex VII: Glossary [Matthews, J.B.R., V. Möller, R. van Diemen, J.S. Fuglestvedt, V. Masson-Delmotte, C.  Méndez, S. Semenov, A. Reisinger (eds.)]. In Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [Masson-Delmotte, V., P. Zhai, A. Pirani, S.L. Connors, C. Péan, S. Berger, N. Caud, Y. Chen, L. Goldfarb, M.I. Gomis, M. Huang, K. Leitzell, E. Lonnoy, J.B.R. Matthews, T.K. Maycock, T. Waterfield, O. Yelekçi, R. Yu, and B. Zhou (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, pp. 2215–2256, doi:10.1017/9781009157896.022.
  8. ^ Canadell, J. G.; Monteiro, P. M. S.; Costa, M. H.; Cotrim da Cunha, L.; Ishii, M.; Jaccard, S.; Cox, P. M.; Eliseev, A. V.; Henson, S.; Koven, C.; Lohila, A.; Patra, P. K.; Piao, S.; Rogelj, J.; Syampungani, S.; Zaehle, S.; Zickfeld, K. (2021). "Global Carbon and Other Biogeochemical Cycles and Feedbacks" (PDF). IPCC AR6 WG1 2021.
  9. ^ Quaas, Johannes; Jia, Hailing; Smith, Chris; Albright, Anna Lea; Aas, Wenche; Bellouin, Nicolas; Boucher, Olivier; Doutriaux-Boucher, Marie; Forster, Piers M.; Grosvenor, Daniel; Jenkins, Stuart; Klimont, Zbigniew; Loeb, Norman G.; Ma, Xiaoyan; Naik, Vaishali; Paulot, Fabien; Stier, Philip; Wild, Martin; Myhre, Gunnar; Schulz, Michael (21 September 2022). "Robust evidence for reversal of the trend in aerosol effective climate forcing". Atmospheric Chemistry and Physics. 22 (18): 12221–12239. Bibcode:2022ACP....2212221Q. doi:10.5194/acp-22-12221-2022. hdl:20.500.11850/572791. S2CID 252446168.
  10. ^ Cao, Yang; Zhu, Yannian; Wang, Minghuai; Rosenfeld, Daniel; Liang, Yuan; Liu, Jihu; Liu, Zhoukun; Bai, Heming (7 January 2023). "Emission Reductions Significantly Reduce the Hemispheric Contrast in Cloud Droplet Number Concentration in Recent Two Decades". Journal of Geophysical Research: Atmospheres. 128 (2): e2022JD037417. Bibcode:2023JGRD..12837417C. doi:10.1029/2022JD037417.