Climate change feedbacks

"Climate feedback" redirects here. For the fact-checking website, see Climate Feedback.
The relative magnitude of the top 6 climate change feedbacks and what they influence. Positive feedbacks amplify the global warming response to greenhouse gas emissions and negative feedbacks reduce it.[1] In this chart, the horizontal lengths of the red and blue bars indicate the strength of respective feedbacks.

Climate change feedbacks are natural processes that impact how much global temperatures will increase for a given amount of greenhouse gas emissions. Positive feedbacks amplify global warming while negative feedbacks diminish it.[2]: 2233  Feedbacks influence both the amount of greenhouse gases in the atmosphere and the amount of temperature change that happens in response. While emissions are the forcing that causes climate change, feedbacks combine to control climate sensitivity to that forcing.[3]: 11 

While the overall sum of feedbacks is negative, it is becoming less negative as greenhouse gas emissions continue. This means that warming is slower than it would be in the absence of feedbacks, but that warming will accelerate if emissions continue at current levels.[4]: 95–96  Net feedbacks will stay negative largely because of increased thermal radiation as the planet warms, which is an effect that is several times larger than any other singular feedback.[4]: 96  Accordingly, anthropogenic climate change alone cannot cause a runaway greenhouse effect.[5][6]

Feedbacks can be divided into physical feedbacks and partially biological feedbacks. Physical feedbacks include decreased surface reflectivity (from diminished snow and ice cover) and increased water vapor in the atmosphere. Water vapor is not only a powerful greenhouse gas, it also influences feedbacks in the distribution of clouds and temperatures in the atmosphere. Biological feedbacks are mostly associated with changes to the rate at which plant matter accumulates CO2 as part of the carbon cycle.[7]: 967  The carbon cycle absorbs more than half of CO2 emissions every year into plants and into the ocean.[8]: 676  Over the long term the percentage will be reduced as carbon sinks become saturated and higher temperatures lead to effects like drought and wildfires.[8]: 698 [4]: 96 [3]: 20 

Feedback strengths and relationships are estimated through global climate models, with their estimates calibrated against observational data whenever possible.[4]: 967  Some feedbacks rapidly impact climate sensitivity, while the feedback response from ice sheets is drawn out over several centuries.[7]: 967  Feedbacks can also result in localized differences, such as polar amplification resulting from feedbacks that include reduced snow and ice cover. While basic relationships are well understood, feedback uncertainty exists in certain areas, particularly regarding cloud feedbacks.[9][10] Carbon cycle uncertainty is driven by the large rates at which CO2 is both absorbed into plants and released when biomass burns or decays. For instance, permafrost thaw produces both CO2 and methane emissions in ways that are difficult to model.[8]: 677  Climate change scenarios use models to estimate how Earth will respond to greenhouse gas emissions over time, including how feedbacks will change as the planet warms.[11]

  1. ^ "(a) Feedbacks in the climate system / (b) Carbon-cycle climate feedbacks". IPCC.ch. Intergovernmental Panel on Climate Change. November 2022. Archived from the original on 2 May 2024. AR6 WG1 Technical Summary Fig. TS-17.
  2. ^ 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.
  3. ^ a b IPCC (2021). "Summary for Policymakers" (PDF). The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change. p. 40. ISBN 978-92-9169-158-6.
  4. ^ a b c d Arias, Paola A.; Bellouin, Nicolas; Coppola, Erika; Jones, Richard G.; Krinner, Gerhard (2021). Technical Summary (PDF). Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change (Report). Cambridge University Press, Cambridge, UK and New York, NY, US. pp. 35–144. doi:10.1017/9781009157896.009. Archived from the original (PDF) on 21 July 2022.
  5. ^ Kang, Sarah M.; Ceppi, Paulo; Yu, Yue; Kang, In-Sik (24 August 2023). "Recent global climate feedback controlled by Southern Ocean cooling". Nature Geoscience. 16 (9): 775–780. Bibcode:2023NatGe..16..775K. doi:10.1038/s41561-023-01256-6. Net climate feedback is negative as the climate system acts to counteract the forcing; otherwise, the system would be unstable.
  6. ^ Scoping of the IPCC 5th Assessment Report Cross Cutting Issues (PDF). Thirty-first Session of the IPCC Bali, 26–29 October 2009 (Report). Archived (PDF) from the original on 9 November 2009. Retrieved 24 March 2019. For instance, a "runaway greenhouse effect"—analogous to Venus--appears to have virtually no chance of being induced by anthropogenic activities.
  7. ^ a b Forster, P.; Storelvmo, T.; Armour, K.; Collins, W.; Dufresne, J.-L.; Frame, D.; Lunt, D.J.; Mauritsen, T.; Watanabe, M.; Wild, M.; Zhang, H. (2021). Masson-Delmotte, V.; Zhai, P.; Pirani, A.; Connors, S. L.; Péan, C.; Berger, S.; Caud, N.; Chen, Y.; Goldfarb, L. (eds.). Chapter 7: The Earth's Energy Budget, Climate Feedbacks, and Climate Sensitivity (PDF). Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change (Report). Cambridge University Press, Cambridge, UK and New York, NY, US. pp. 923–1054. doi:10.1017/9781009157896.009.
  8. ^ a b c Cite error: The named reference IPCC AR6 WG1 CH5 was invoked but never defined (see the help page).
  9. ^ Cite error: The named reference Zelinka2020 was invoked but never defined (see the help page).
  10. ^ Cite error: The named reference SD2020 was invoked but never defined (see the help page).
  11. ^ Scott Johnson (September 17, 2019). "2°C is not known to be a "point of no return", as Jonathan Franzen claims". Science Feedback. Climate Feedback. Retrieved September 16, 2024.