Editorial Type:
Article
Article Type:
Research Article

A New Method of Comparing Forcing Agents in Climate Models

Ben Kravitz Atmospheric Sciences and Global Change Division, Pacific Northwest National Laboratory, Richland, Washington

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Douglas G. MacMartin Department of Computing and Mathematical Sciences, California Institute of Technology, Pasadena, California

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Philip J. Rasch Atmospheric Sciences and Global Change Division, Pacific Northwest National Laboratory, Richland, Washington

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Andrew J. Jarvis Lancaster Environment Centre, University of Lancaster, Lancaster, United Kingdom

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Print Publication:
15 Oct 2015
DOI:
https://doi.org/10.1175/JCLI-D-14-00663.1
Page(s):
8203–8218
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Abstract

The authors describe a new method of comparing different climate forcing agents (e.g., CO2 concentration, CH4 concentration, and total solar irradiance) in climate models that circumvents many of the difficulties associated with explicit calculations of efficacy. This is achieved by introducing an explicit feedback loop external to a climate model that adjusts one forcing agent to balance another while keeping global-mean surface temperature constant. The convergence time of this feedback loop can be adjusted, allowing for comparisons of forcing agents to be achieved with relatively short simulations. Comparisons between forcing agents are highly linear in concordance with predicted scaling relationships; for example, the global-mean climate response to a doubling of the CO2 concentration is equivalent to that of a 2.1% change in total solar irradiance. This result is independent of the magnitude of the forcing agent (within the range of radiative forcings considered here) and is consistent across two different climate models.

Denotes Open Access content.

Supplemental information related to this paper is available at the Journals Online website: http://dx.doi.org/10.1175/JCLI-D-14-00663.s1.

Corresponding author address: Ben Kravitz, Atmospheric Sciences and Global Change Division, Pacific Northwest National Laboratory, P.O. Box 999, MSIN K9-30, Richland, WA 99352. E-mail: ben.kravitz@pnnl.gov

Abstract

The authors describe a new method of comparing different climate forcing agents (e.g., CO2 concentration, CH4 concentration, and total solar irradiance) in climate models that circumvents many of the difficulties associated with explicit calculations of efficacy. This is achieved by introducing an explicit feedback loop external to a climate model that adjusts one forcing agent to balance another while keeping global-mean surface temperature constant. The convergence time of this feedback loop can be adjusted, allowing for comparisons of forcing agents to be achieved with relatively short simulations. Comparisons between forcing agents are highly linear in concordance with predicted scaling relationships; for example, the global-mean climate response to a doubling of the CO2 concentration is equivalent to that of a 2.1% change in total solar irradiance. This result is independent of the magnitude of the forcing agent (within the range of radiative forcings considered here) and is consistent across two different climate models.

Denotes Open Access content.

Supplemental information related to this paper is available at the Journals Online website: http://dx.doi.org/10.1175/JCLI-D-14-00663.s1.

Corresponding author address: Ben Kravitz, Atmospheric Sciences and Global Change Division, Pacific Northwest National Laboratory, P.O. Box 999, MSIN K9-30, Richland, WA 99352. E-mail: ben.kravitz@pnnl.gov

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