Climate commitment

Short description: Unavoidable future climate change due to inertial effects

The ongoing buildup of long-lived greenhouse gases in Earth's atmosphere, whose warming influence has nearly doubled since 1979, shows mankind's influence on the global climate.[1][2][3]

Climate commitment describes the fact that Earth's climate reacts with a delay to influencing factors ("climate forcings") such as the growth and the greater presence of greenhouse gases. Climate commitment studies attempt to assess the amount of future global warming that is "committed" under the assumption of some constant or some evolving level of forcing. The constant level often used for illustrative purposes is that due to CO
2 doubling or quadrupling relative to the pre-industrial level; or the present level of forcing.

## Contents

* 1 Definition
* 2 Basic idea
* 3 Models
* 4 History
* 5 Misuse
* 6 See also
* 7 References
* 8 External links

## Definition

Climate commitment is the "unavoidable future climate change resulting from inertia in the geophysical and socio-economic systems".[4] Different types of climate change commitment are discussed in the literature. These include the "constant composition commitment"; the "constant emissions commitment" and the "zero emissions commitment".[4]: 2222

## Basic idea

The accumulation of excess heat in the ocean, at ever greater depths, measures global warming that has already become "irreversible" in the near term[5]

If a perturbation — such as an increase in greenhouse gases or solar activity — is applied to Earth's climate system the response will not be immediate, principally because of the large heat capacity and thermal inertia of the oceans.[6]

As an analogue, consider the heating of a thin metal plate (by the sun or by a flame): the plate will warm relatively quickly. If a thick metal block is heated instead, it will take much longer for the entire block to reach equilibrium with the imposed heating because of its higher heat capacity.

Land only stores heat in the top few meters. Ocean water, by contrast, can move vertically and store heat within the ocean's depth (convection). This is why the land surface is observed to warm more than the oceans. It also explains the large difference in global surface temperature response between

* "transient" climate simulations in which the planet's incoming/outgoing energy flows are substantially out-of-balance and only a shallow ocean model might be utilized, and
* "equilibrium" climate simulations in which the energy flows approach a new balance and a full ocean model is needed.[7][8]

The "commitment" can apply to variables other than temperature: because of the long mixing time for heat into the deep ocean, a given surface warming commits to centuries of sea level rise from thermal expansion of the ocean. Also once a certain threshold is crossed, it is likely that a slow melting of the Greenland ice sheet will commit us to a sea level rise of 5m over millennia.[citation needed]

## Models

Recent models forecast that even in the unlikely event of greenhouse gases stabilizing at present levels, the Earth would warm by an additional 0.5°C by 2100, a similar rise in temperature to that seen during the 20th century. In 2050, as much as 64% of that commitment would be due to past natural forcings. Over time, their contribution compared to the human influence will diminish. Overall, the warming commitment at 2005 greenhouse gas levels could exceed 1°C.[9] As ocean waters expand in response to this warming, global sea levels would mount by about 10 centimeters during that time. These models do not take into account ice cap and glacier melting; including those climate feedback effects would give a 1–1.5°C estimated temperature increase.[10]

## History

The concept has been discussed as far back as 1995 in the IPCC TAR [1] and in the SAR.

## Misuse

Climate commitment studies span a range of emissions scenarios which are intimately tied to past, present and future human choices. The "commitment" concept is misused when worst cases are asserted to be inevitable regardless of social agency. Models rather indicate that additional surface warming can be halted almost simultaneous with rapid emissions reductions.[11]

## See also

* Climate change scenario
* Climate inertia
* Climate sensitivity

## References

* Wetherald, Richard T.; Stouffer, Ronald J.; Dixon, Keith W. (2001). "Committed warming and its implications for climate change.". Geophysical Research Letters 28 (8): 1535–8. doi:10.1029/2000gl011786. Bibcode: 2001GeoRL..28.1535W. https://www.gfdl.noaa.gov/bibliography/related_files/rw0101.pdf.
* Meehl, Gerald A.; Washington, Warren M.; Collins, William D.; Arblaster, Julie M.; Hu, Aixue; Buja, Lawrence E.; Strand, Warren G.; Teng, Haiyan (17 March 2005). "How Much More Global Warming and Sea Level Rise?". Science 307 (5716): 1769–72. doi:10.1126/science.1106663. PMID 15774757. Bibcode: 2005Sci...307.1769M. http://www.geo.utexas.edu/courses/387h/PAPERS/meehl2005.pdf.

1. ↑ "The NOAA Annual Greenhouse Gas Index (AGGI)". National Oceanic and Atmospheric Administration (NOAA). 2024. https://gml.noaa.gov/aggi/aggi.html.
2. ↑ "Annual Greenhouse Gas Index". U.S. Global Change Research Program. https://www.globalchange.gov/browse/indicators/annual-greenhouse-gas-index.
3. ↑ "The NOAA Annual Greenhouse Gas Index (AGGI) - An Introduction". NOAA Global Monitoring Laboratory/Earth System Research Laboratories. https://www.esrl.noaa.gov/gmd/aggi/.
4. ↑ 4.0 4.1 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.
5. ↑ von Schuckmann, K.; Cheng, L.; Palmer, M. D.; Hansen, J. et al. (7 September 2020). "Heat stored in the Earth system: where does the energy go?". Earth System Science Data 12 (3): 2013-2041. doi:10.5194/essd-12-2013-2020. Bibcode: 2020ESSD...12.2013V.
6. ↑ Abraham, John; Cheng, Lijing; Mann, Michael E.; Trenberth, Kevin; von Schuckmann, Karina (1 July 2022). "The ocean response to climate change guides both adaptation and mitigation efforts". Atmospheric and Oceanic Science Letters 15 (100221): 1–9. doi:10.1016/j.aosl.2022.100221. Bibcode: 2022AOSL...1500221A.
7. ↑ Royce, B. S. H.; Lam, S. H. (25 July 2013). "The Earth's Equilibrium Climate Sensitivity and Thermal Inertia". arXiv:1307.6821 [physics.ao-ph].
8. ↑ Hansen, J.; Russell, G.; Lacis, A.; Fung, I.; Rind, D.; Stone, P. (1985). "Climate response times: Dependence on climate sensitivity and ocean mixing". Science 229 (4716): 857–850. doi:10.1126/science.229.4716.857. PMID 17777925. Bibcode: 1985Sci...229..857H. https://pubs.giss.nasa.gov/docs/1985/1985_Hansen_ha09600g.pdf.
9. ↑ Wigley, T. M. L. (17 March 2005). "The Climate Change Commitment". Science 307 (5716): 1766–9. doi:10.1126/science.1103934. PMID 15774756. Bibcode: 2005Sci...307.1766W. ftp://ftp.soest.hawaii.edu/coastal/Climate Articles/Wigley_2005 Sea level commitment.pdf.
10. ↑ Lockwood, Deirdre (2005-05-17). "Oceans extend effects of climate change". Nature News. doi:10.1038/news050314-13. http://www.nature.com/news/2005/050314/full/050314-13.html.
11. ↑ Mathews, H. Damon; Solomon, Susan (26 April 2013). "Irreversible Does Not Mean Unavoidable". Science (American Association for the Advancement of Science) 340 (6131): 438–439. doi:10.1126/science.1236372. PMID 23539182. Bibcode: 2013Sci...340..438M. https://www.science.org/cms/asset/7446d1ba-b4b9-4c2d-945b-ea04ca0547d6/pap.pdf.

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