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What Determines the Warming Commitment after Cessation of CO2 Emissions?

Resource type
Date created
2017-01-23
Authors/Contributors
Abstract
Previous studies have shown that global mean surface air temperature remains elevated after cessation of CO2 emissions. However, studies differ in whether the temperature continues to increase, slowly decreases, or remains constant after cessation of emissions. An understanding of this committed warming is of importance because it has implication for the estimation of carbon budgets compatible with temperature targets. Here, we investigate the effect of the state of thermal and bio-geochemical equilibration at the time emissions are set to zero on the committed warming as the latter is determined by the balance of these two equilibration processes. We find that the effect of thermal equilibration, expressed as fraction of realized warming, dominates over the bio-geochemical equilibration, expressed as ratio of the airborne fraction to the equilibrium airborne fraction. This leads to a positive warming commitment, and a commitment that declines the later emissions are zeroed along a trajectory of constant atmospheric CO2 concentration. We furthermore show that the scenario prior to zeroed emissions has the strongest effect on the warming commitment, compared to the time of zeroed emissions and the time horizon over which the commitment is calculated.
Document
Published as
Ehlert, Dana & Zickfeld, Kirsten. (2017). What determines the warming commitment after cessation of CO 2 emissions?. Environmental Research Letters. 12. 015002. DOI: 10.1088/1748-9326/aa564a.Previous studies have shown that global mean surface air temperature remains elevated after cessation of CO2 emissions. However, studies differ in whether the temperature continues to increase, slowly decreases, or remains constant after cessation of emissions. An understanding of this committed warming is of importance because it has implication for the estimation of carbon budgets compatible with temperature targets. Here, we investigate the effect of the state of thermal and bio-geochemical equilibration at the time emissions are set to zero on the committed warming as the latter is determined by the balance of these two equilibration processes. We find that the effect of thermal equilibration, expressed as fraction of realized warming, dominates over the bio-geochemical equilibration, expressed as ratio of the airborne fraction to the equilibrium airborne fraction. This leads to a positive warming commitment, and a commitment that declines the later emissions are zeroed along a trajectory of constant atmospheric CO2 concentration. We furthermore show that the scenario prior to zeroed emissions has the strongest effect on the warming commitment, compared to the time of zeroed emissions and the time horizon over which the commitment is calculated.
Publication title
Environmental Research Letters
Document title
What Determines the Warming Commitment after Cessation of CO2 Emissions?
Date
2017
Volume
12
Publisher DOI
10.1088/1748-9326/aa564a
Copyright statement
Copyright is held by the author(s).
Scholarly level
Peer reviewed?
Yes
Language
English
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