Climate commitment: Difference between revisions

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{{short description|Unavoidable future climate change due to inertial effects}}

[[File:1979- Radiative forcing - climate change - global warming - EPA NOAA.svg |thumb|right|upright=1.5 |The ongoing buildup of [[IPCC list of greenhouse gases|long-lived greenhouse gases]] in Earth's atmosphere, whose warming influence has nearly doubled since 1979, shows mankind's influence on the global climate.<ref name=NOAA_AGGI_2023>{{cite web |title=The NOAA Annual Greenhouse Gas Index (AGGI) |url=https://gml.noaa.gov/aggi/aggi.html |website=NOAA.gov |publisher=National Oceanic and Atmospheric Administration (NOAA) |archive-url=https://web.archive.org/web/20241005195609/https://gml.noaa.gov/aggi/aggi.html |archive-date=5 October 2024 |date=2024 |url-status=live }}</ref><ref>{{Cite web |url=https://www.globalchange.gov/browse/indicators/annual-greenhouse-gas-index |title=Annual Greenhouse Gas Index |publisher=U.S. Global Change Research Program |archive-date=21 April 2021 |archive-url=https://web.archive.org/web/20210421143115/https://www.globalchange.gov/browse/indicators/annual-greenhouse-gas-index |url-status=livedead }}</ref><ref>{{Cite web |url=https://www.esrl.noaa.gov/gmd/aggi/ |title=The NOAA Annual Greenhouse Gas Index (AGGI) - An Introduction |publisher=[[NOAA]] Global Monitoring Laboratory/Earth System Research Laboratories |access-date=2 March 2023}}</ref>]]

'''Climate commitment''' describes the fact that Earth's [[climate]] reacts with a delay to influencing factors ("[[climate forcing]]s") such as the growth and the greater presence of [[greenhouse gas]]es. 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 [[carbon dioxide|{{CO2}}]] doubling or quadrupling relative to the pre-industrial level; or the present level of forcing.

{{clear}}

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== Basic idea ==

[[File:Earth's Heat Accumulation.png|thumb|right|upright=1.2|The accumulation of [[ocean heat content|excess heat in the ocean]], at ever greater depths, measures global warming that has already become "irreversible" in the near term<ref name=EarthSysSciData_20200907>{{cite journal |last1=von Schuckmann |first1=K. |last2=Cheng |first2=L. |last3=Palmer |first3=M. D. |last4=Hansen |first4=J. |last5=Tassone |first5=C. |last6=Aich |first6=V. |last7=Adusumilli |first7=S. |last8=Beltrami |first8=H. |last9=Boyer |first9=T. |last10=Cuesta-Valero |first10=F. J. |display-authors=4 |title=Heat stored in the Earth system: where does the energy go? |journal=Earth System Science Data |date=7 September 2020 |doi=10.5194/essd-12-2013-2020 |doi-access=free |volume=12 |issue=3 |page=2013-2041 |bibcode=2020ESSD...12.2013V |hdl=20.500.11850/443809 |hdl-access=free }}</ref>]]

If a [[wiktionary:perturbation|perturbation]] — such as an increase in greenhouse gases or [[solar variation|solar activity]] — is applied to Earth's [[climate system]] the response will not be immediate, principally because of the large [[heat capacity]] (i.e.,and [[Volumetric heat capacity#Thermal inertia|thermal inertia]]) of the [[ocean]]s.<ref>{{cite journal |last1=Abraham |first1=John |last2=Cheng |first2=Lijing |last3=Mann |first3=Michael E. |last4=Trenberth |first4=Kevin |last5=von Schuckmann |first5=Karina |title=The ocean response to climate change guides both adaptation and mitigation efforts |journal=Atmospheric and Oceanic Science Letters |volume=15 |number=100221 |pages=1-9 |date=1 July 2022 |doi=10.1016/j.aosl.2022.100221 |doi-access=free}}</ref>

:''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 [[Thermodynamic equilibrium|equilibrium]] with the imposed heating because of its higher heat capacity.''

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* "[[Equilibrium state|equilibrium]]" climate simulations in which the energy flows approach a new balance and a full ocean model is needed.<ref>{{cite arXiv | eprint = 1307.6821|title=The Earth's Equilibrium Climate Sensitivity and Thermal Inertia|date=25 July 2013| first1 = B. S. H. | last1 = Royce | first2 = S. H. | last2 = Lam |class=physics.ao-ph}}</ref><ref>{{cite journal |last1=Hansen |first1=J. |last2=Russell |first2=G. |last3=Lacis |first3=A. |last4=Fung |first4=I. |last5=Rind |first5=D. |last6=Stone |first6=P. |url=https://pubs.giss.nasa.gov/docs/1985/1985_Hansen_ha09600g.pdf |title=Climate response times: Dependence on climate sensitivity and ocean mixing |journal=Science |volume=229 |pages=857–850 |year=1985 |issue=4716 |doi=10.1126/science.229.4716.857 |pmid=17777925 |bibcode=1985Sci...229..857H|s2cid=22938919 }}</ref>

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.{{cn|date=November 2024}}

== Models ==

{{main|global climate model}}

Recent [[model (abstract)|model]]s 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.<ref>{{cite journal |last=Wigley |first=T. M. L. |title=The Climate Change Commitment |journal=Science |volume=307 |issue=5716 |pages=1766–9 |date=17 March 2005 |doi=10.1126/science.1103934 |pmid=15774756 |url=ftp://ftp.soest.hawaii.edu/coastal/Climate%20Articles/Wigley_2005%20Sea%20level%20commitment.pdf |archive-url=https://web.archive.org/web/20171011182247/ftp://ftp.soest.hawaii.edu/coastal/Climate%20Articles/Wigley_2005%20Sea%20level%20commitment.pdf |archive-date=2017-10-11 |url-status=dead |bibcode=2005Sci...307.1766W }}</ref> As ocean waters expand in response to this warming, global [[sea level]]s 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.<ref>{{cite journal |url= http://www.nature.com/news/2005/050314/full/050314-13.html |title= Oceans extend effects of climate change |first=Deirdre |last=Lockwood |date= 2005-05-17 |journal=Nature News |doi=10.1038/news050314-13|url-access=subscription }} </ref>

== History ==

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== Misuse ==

Climate commitment studies span a range of possible[[Shared outcomesSocioeconomic Pathways|emissions scenarios]] which are intimately tied to past, present and future human choices. The "commitment" concept can beis misused if used to assert thatwhen worst cases are unavoidableasserted to be inevitable regardless of societal [[agency (sociology)|social agency]]. Models rather indicate that additional surface warming can be halted almost simultaneous with rapid emissions reductions in emissions.<ref>{{cite journal |url=https://www.science.org/cms/asset/7446d1ba-b4b9-4c2d-945b-ea04ca0547d6/pap.pdf |title=Irreversible Does Not Mean Unavoidable |last1=Mathews |first1=H. Damon |last2=Solomon |first2=Susan |journal=Science |publisher=American Association for the Advancement of Science |volume=340 |issue=6131 |pages=438–439 |date=26 April 2013 |doi=10.1126/science.1236372|pmid=23539182 |bibcode=2013Sci...340..438M |s2cid=44352274 }}</ref>

== See also ==

* [[Climate change scenario]]

* [[Climate inertia]]

* [[Climate sensitivity]]