Continued global warming after CO2 emissions stoppage

Abstract

Stopping anthropogenic carbon emissions will not result in a sudden decrease in temperature. Earth system models are used to show that there may be an increase in warming after an initial decrease. This is a result of feedbacks from decreased ocean heat uptake, which exceed the cooling from decreased atmospheric CO2. Recent studies have suggested that global mean surface temperature would remain approximately constant on multi-century timescales after CO2 emissions1,2,3,4,5,6,7,8,9 are stopped. Here we use Earth system model simulations of such a stoppage to demonstrate that in some models, surface temperature may actually increase on multi-century timescales after an initial century-long decrease. This occurs in spite of a decline in radiative forcing that exceeds the decline in ocean heat uptake—a circumstance that would otherwise be expected to lead to a decline in global temperature. The reason is that the warming effect of decreasing ocean heat uptake together with feedback effects arising in response to the geographic structure of ocean heat uptake10,11,12 overcompensates the cooling effect of decreasing atmospheric CO2 on multi-century timescales. Our study also reveals that equilibrium climate sensitivity estimates based on a widely used method of regressing the Earth’s energy imbalance against surface temperature change13,14 are biased. Uncertainty in the magnitude of the feedback effects associated with the magnitude and geographic distribution of ocean heat uptake therefore contributes substantially to the uncertainty in allowable carbon emissions for a given multi-century warming target.

Cite this article

Frölicher, T., Winton, M. & Sarmiento, J. Continued global warming after CO₂ emissions stoppage. Nature Clim Change 4, 40–44 (2014). https://doi.org/10.1038/nclimate2060

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