climate inertia

The paleoclimate record shows that Earth's climate system has evolved along various pathways and with multiple timescales. Its relatively stable states which can persist for many millennia have been interrupted by short to long transitional periods of relative instability.{{cite book |title=Abrupt Climate Change: Inevitable Surprises |author=National Research Council |publisher=The National Academic Press |year=2002 |doi=10.17226/10136 |isbn=978-0-309-13304-3}}{{rp|19–72}} Studies of climate sensitivity and inertia are concerned with quantifying the most basic manner in which a sustained forcing perturbation will cause the system to deviate within or initially away from its relatively stable state of the present Holocene epoch.{{cite journal |last1=Marcott |first1=Shaun A. |last2=Shakun |first2=Jeremy D. |last3=Clark |first3=Peter U. |last4=Mix |first4=Alan C. |date=8 March 2013 |title=A Reconstruction of Regional and Global Temperature for the Past 11,300 Years |url=https://www.science.org/doi/10.1126/science.1228026 |journal=Science |volume=339 |issue=6124 |pages=1198–1201 |doi=10.1126/science.1228026 |pmid=23471405 |bibcode=2013Sci...339.1198M |s2cid=29665980|citeseerx=10.1.1.383.902 }}{{cite journal |last1=Steffen |first1=Will |last2=Rockström |first2=Johan |last3=Richardson |first3=Katherine |last4=Lenton |first4=Timothy M. |last5=Folke |first5=Carle |last6=Liverman |first6=Diana |last7=Summerhayes |first7=Collin P. |last8=Barnosky |first8=Anthony D. |last9=Cornell |first9=Sarah E. |last10=Crucifix |first10=Michel |last11=Donges |first11=Jonathan F. |last12=Fetzer |first12=Ingo |last13=Lade |first13=Steven J. |last14=Scheffer |first14=Marten |last15=Winkelmann |first15=Ricarda |last16=Schellnhuber |first16=Hans Joachim |display-authors=10 |title=Trajectories of the Earth System in the Anthropocene |journal=PNAS |volume=116 |issue=33 |pages=8252–8259 |date=6 August 2018 |doi=10.1073/pnas.1810141115 |pmid=30082409 |pmc=6099852 |bibcode=2018PNAS..115.8252S |doi-access=free}}

"Time constants" are useful metrics for summarizing the first-order (linear) impacts of the various inertial phenomena within both simple and complex systems. They quantify the time after which 63% of a full output response occurs following the step change of an input. They are observed from data or can be estimated from numerical simulation or a lumped system analysis. In climate science these methods can be applied to Earth's energy cycle, water cycle, carbon cycle and elsewhere. For example, heat transport and storage in the ocean, cryosphere, land and atmosphere are elements within a lumped thermal analysis.{{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 }}{{cite book |title=Physically-based Modelling and Simulation of Climate and Climatic Change |editor=Michael E. Schlesinger |author=Gerald R. North |chapter=Lessons from energy balance models |edition=NATO Advanced Study Institute on Physical-Based Modelling |publisher=Springer |year=1988 |isbn=978-90-277-2789-3}}{{rp|627}} Response times to radiative forcing via the atmosphere typically increase with depth below the surface.

Inertial time constants indicate a base rate for forced changes, but lengthy values provide no guarantee of long-term system evolution along a smooth pathway. Numerous higher-order tipping elements having various trigger thresholds and transition timescales have been identified within Earth's present state.{{cite journal |last1=Lenton |first1=Timothy M. |last2=Held |first2=Hermann |last3=Kriegler |first3=Elmar |last4=Hall |first4=Jim W |last5=Lucht |first5=Wolfgang |last6=Rahmstorf |first6=Stefan |last7=Schellnhuber |first7=Hans Joachim |title=Tipping elements in the Earth's climate system |journal=PNAS |date=2008-02-12 |volume=105 |issue=6 |pages=1786–1793 |doi=10.1073/pnas.0705414105 |pmid=18258748 |pmc=2538841 |bibcode=2008PNAS..105.1786L |doi-access=free }}{{Cite journal |last1=Armstrong McKay |first1=David|last2=Abrams |first2=Jesse |last3=Winkelmann |first3=Ricarda |last4=Sakschewski |first4=Boris |last5=Loriani |first5=Sina |last6=Fetzer |first6=Ingo|last7=Cornell|first7=Sarah |last8=Rockström |first8=Johan |last9=Staal |first9=Arie |last10=Lenton |first10=Timothy |date=9 September 2022 |title=Exceeding 1.5°C global warming could trigger multiple climate tipping points |url=https://www.science.org/doi/10.1126/science.abn7950 |journal=Science |language=en |volume=377 |issue=6611 |pages=eabn7950 |doi=10.1126/science.abn7950 |pmid=36074831 |hdl=10871/131584 |s2cid=252161375 |issn=0036-8075|hdl-access=free }} Such events might precipitate a nonlinear rearrangement of internal energy flows along with more rapid shifts in climate and/or other systems at regional to global scale.{{rp|10–15, 73–76}}

The response of global surface temperature (GST) to a step-like doubling of the atmospheric {{CO2}} concentration, and its resultant forcing, is defined as the Equilibrium Climate Sensitivity (ECS). The ECS response extends over short and long timescales, however the main time constant associated with ECS has been identified by Jule Charney, James Hansen and others as a useful metric to help guide policymaking.{{Cite book |author1=Charney, J.G. |author2=Arakawa, A. |author3=Baker D.J. |author4=Bolin B. |author5=Dickinson R.E. |author6=Goody R.M. |author7=Leith C.E. |author8=Stommel H.M. |author9=Wunsch C.I. |title=Carbon Dioxide and Climate: A Scientific Assessment |url=https://nap.nationalacademies.org/catalog/12181/carbon-dioxide-and-climate-a-scientific-assessment |format=Free PDF download |year=1979 |publisher=National Academies Press |location=Washington D.C., United States |doi=10.17226/12181|isbn=978-0-309-11910-8 }} RCPs, SSPs, and other similar scenarios have also been used by researchers to simulate the rate of forced climate changes. By definition, ECS presumes that ongoing emissions will offset the ocean and land carbon sinks following the step-wise perturbation in atmospheric {{CO2}}.{{cite journal |last1=Sherwood |first1=S.C. |last2=Webb |first2=M.J. |last3=Annan |first3=J.D. |last4=Armour |first4=K.C. |last5=Forster |first5=P.M. |last6=Hargreaves |first6=J.C. |last7=Hegerl |first7=G. |last8=Klein |first8=S.A. |last9=Marvel |first9=K.D. |last10=Rohling |first10=E.J. |last11=Watanabe |first11=M. |last12=Andrews |first12=T. |last13=Braconnot |first13=P. |last14=Bretherton |first14=C.S. |last15=Foster |first15=G.L. |last16=Hausfather |first16=Z. |last17=von der Heydt |first17=A.S. |last18=Knutti |first18=R. |last19=Mauritsen |first19=T. |last20=Norris |first20=J.R. |last21=Proistosescu |first21=C. |last22=Rugenstein |first22=M. |last23=Schmidt |first23=G.A. |last24=Tokarska |first24=K.B. |last25=Zelinka |first25=M.D. |display-authors=10 |title=An Assessment of Earth's Climate Sensitivity Using Multiple Lines of Evidence |journal=Reviews of Geophysics |volume=58 |issue=4 |date=22 July 2020 |pages=e2019RG000678 |doi=10.1029/2019RG000678 |pmid=33015673 |pmc=7524012 |bibcode=2020RvGeo..5800678S |doi-access=free}}

ECS response time is proportional to ECS and is principally regulated by the thermal inertia of the uppermost mixed layer and adjacent lower ocean layers. Main time constants fitted to the results from climate models have ranged from a few decades when ECS is low, to as long as a century when ECS is high. A portion of the variation between estimates arises from different treatments of heat transport into the deep ocean.

{{Expand section|date=February 2023}}

File:Earth's Heat Accumulation.png Material was copied from this source, which is available under a [https://creativecommons.org/licenses/by/4.0/ Creative Commons Attribution 4.0 International License]|bibcode=2020ESSD...12.2013V |hdl=20.500.11850/443809 |hdl-access=free }} The rate of rise has been partially slowed by the system's thermal inertia.]]

Thermal inertia is a term which refers to the observed delays in a body's temperature response during heat transfers. A body with large thermal inertia can store a big amount of energy because of its heat capacity, and can effectively transmit energy according to its heat transfer coefficient. The consequences of thermal inertia are inherently expressed via many climate change feedbacks because of their temperature dependencies; including through the strong stabilizing feedback of the Planck response''.

The global ocean is Earth's largest thermal reservoir that functions to regulate the planet's climate; acting as both a sink and a source of energy. The ocean's thermal inertia delays some global warming for decades or centuries. It is accounted for in global climate models, and has been confirmed via measurements of ocean heat content.{{Cite journal |last1=Cheng |first1=Lijing |last2=Foster |first2=Grant |last3=Hausfather |first3=Zeke |last4=Trenberth |first4=Kevin E. |last5=Abraham |first5=John |date=2022 |title=Improved Quantification of the Rate of Ocean Warming |journal=Journal of Climate |volume=35 |issue=14 |pages=4827–4840 |bibcode=2022JCli...35.4827C |doi=10.1175/JCLI-D-21-0895.1 |doi-access=free}} The observed transient climate sensitivity is proportional to the thermal inertia time scale of the shallower ocean.{{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}}

Even after {{CO2}} emissions are lowered, the melting of ice sheets will persist and further increase sea-level rise for centuries. The slower transportation of heat into the extreme deep ocean, subsurface land sediments, and thick ice sheets will continue until the new Earth system equilibrium has been reached.{{cite web|url=http://www.ipcc.ch/ipccreports/tar/vol4/011.htm|title=Climate Change 2001: Synthesis Report|year=2001|work=IPCC|access-date=11 May 2015}}

Permafrost also takes longer to respond to a warming planet because of thermal inertia, due to ice rich materials and permafrost thickness.{{cite news | last = M. W. | first = Smith | date = 1988 | title = The significance of climatic change for the permafrost environment | citeseerx = 10.1.1.383.5875 | page = 19 }}

{{See also|Climate change feedback#Carbon cycle}}

File:Atmospheric CO2 impulse response.svg following a 100 GtC injection of {{CO2}} into Earth's atmosphere.{{Cite journal |last1=Joos |first1=F. |last2=Roth |first2=R. |last3=Fuglestvedt |first3=J.S. |last4=Peters |first4=G.P. |last5=Enting |first5=I.G. |display-authors=etal |title=Carbon dioxide and climate impulse response functions for the computation of greenhouse gas metrics: A multi-model analysis |journal=Atmospheric Chemistry and Physics |date=8 March 2013 |doi=10.5194/acpd-12-19799-2012 |doi-access=free |url=https://www.atmos-chem-phys.net/13/2793/2013/ |volume=13 |issue=5 |pages=2793–2825 50px Material was copied from this source, which is available under a [https://creativecommons.org/licenses/by/3.0/ Creative Commons Attribution 3.0 Unported License] |hdl=20.500.11850/58316 |hdl-access=free }} The relative inertial effect of positive vs. negative feedback during early years is indicated by the pulse fraction which ultimately remains.]]

Earth's carbon cycle feedback includes a destabilizing positive feedback (identified as the climate-carbon feedback) which prolongs warming for centuries, and a stabilizing negative feedback (identified as the concentration-carbon feedback) which limits the ultimate warming response to fossil carbon emissions. The near-term effect following emissions is asymmetric with latter mechanism being about four times larger,{{cite journal |last= Archer |first= David |title= Atmospheric lifetime of fossil fuel carbon dioxide |journal= Annual Review of Earth and Planetary Sciences |volume= 37 |pages= 117–34 |year= 2009 |issue= 1 |doi= 10.1146/annurev.earth.031208.100206| bibcode = 2009AREPS..37..117A |hdl= 2268/12933 |url= https://orbi.uliege.be/handle/2268/12933|hdl-access= free }} and results in a significant net slowing contribution to the inertia of the climate system during the first few decades following emissions.

{{Main|Ecological stability|Ecological resilience}}

Depending on the ecosystem, effects of climate change could show quickly, while others take more time to respond. For instance, coral bleaching can occur in a single warm season, while trees may be able to persist for decades under a changing climate, but be unable to regenerate. Changes in the frequency of extreme weather events could disrupt ecosystems as a consequence, depending on individual response times of species.

The IPCC concluded that the inertia and uncertainty of the climate system, ecosystems, and socioeconomic systems implies that margins for safety should be considered. Thus, setting strategies, targets, and time tables for avoiding dangerous interference through climate change. Further the IPCC concluded in their 2001 report that the stabilization of atmospheric {{CO2}} concentration, temperature, or sea level is affected by:

• The inertia of the climate system, which will cause climate change to continue for a period after mitigation actions are implemented.{{cite journal |last1=Samset |first1=B.H. |last2=Fuglestvedt |first2=J.S. |last3=Lund |first3=M.T.|title=Delayed emergence of a global temperature response after emission mitigation |journal=Nature Communications |volume=11 |number=3261 |date=7 July 2020 |page=3261 |doi=10.1038/s41467-020-17001-1 |pmid=32636367 |pmc=7341748 |bibcode=2020NatCo..11.3261S |doi-access=free}}
• Uncertainty regarding the location of possible thresholds of irreversible change and the behavior of the system in their vicinity.
• The time lags between adoption of mitigation goals and their achievement.

• Earth's energy budget
• Planetary boundaries
• Systems theory and Systems analysis

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