Abstract
JOURNAL OF GEOPHYSICAL RESEARCH,
VOL. 110,
D18104,
45 PP., 2005
doi:10.1029/2005JD005776
Efficacy of climate forcings
NASA Goddard Institute for Space Studies, New York, New York, USA
Columbia University Earth Institute, New York, New York, USA
Columbia University Earth Institute, New York, New York, USA
SGT Incorporated, New York, New York, USA
Columbia University Earth Institute, New York, New York, USA
NASA Goddard Institute for Space Studies, New York, New York, USA
Department of Earth and Environmental Sciences, Columbia University, New York, New York, USA
NASA Goddard Institute for Space Studies, New York, New York, USA
Department of Earth and Environmental Sciences, Columbia University, New York, New York, USA
NASA Goddard Institute for Space Studies, New York, New York, USA
Columbia University Earth Institute, New York, New York, USA
Columbia University Earth Institute, New York, New York, USA
Columbia University Earth Institute, New York, New York, USA
Columbia University Earth Institute, New York, New York, USA
Department of Applied Physics and Applied Mathematics, Columbia University, New York, New York, USA
NASA Goddard Institute for Space Studies, New York, New York, USA
Columbia University Earth Institute, New York, New York, USA
SGT Incorporated, New York, New York, USA
NASA Goddard Institute for Space Studies, New York, New York, USA
Department of Earth and Environmental Sciences, Columbia University, New York, New York, USA
Columbia University Earth Institute, New York, New York, USA
NASA Goddard Space Flight Center, Greenbelt, Maryland, USA
Laboratoire des Sciences du Climat et de l'Environnement, Orme des Merisiers, Gif-sur-Yvette, France
NASA Goddard Institute for Space Studies, New York, New York, USA
Department of Applied Physics and Applied Mathematics, Columbia University, New York, New York, USA
NASA Goddard Space Flight Center, Greenbelt, Maryland, USA
Laboratoire des Sciences du Climat et de l'Environnement, Orme des Merisiers, Gif-sur-Yvette, France
NASA Goddard Institute for Space Studies, New York, New York, USA
Columbia University Earth Institute, New York, New York, USA
Department of Geology, Yale University, New Haven, Connecticut, USA
Naval Research Laboratory, Washington, D. C., USA
Columbia University Earth Institute, New York, New York, USA
SGT Incorporated, New York, New York, USA
Lawrence Berkeley National Laboratory, Berkeley, California, USA
NASA Goddard Institute for Space Studies, New York, New York, USA
Department of Applied Physics and Applied Mathematics, Columbia University, New York, New York, USA
NASA Langley Research Center, Hampton, Virginia, USA
Lawrence Berkeley National Laboratory, Berkeley, California, USA
SGT Incorporated, New York, New York, USA
Department of Applied Physics and Applied Mathematics, Columbia University, New York, New York, USA
Columbia University Earth Institute, New York, New York, USA
NASA Goddard Institute for Space Studies, New York, New York, USA
Department of Earth and Environmental Sciences, Columbia University, New York, New York, USA
NASA Goddard Institute for Space Studies, New York, New York, USA
Department of Earth and Environmental Sciences, Columbia University, New York, New York, USA
NASA Goddard Institute for Space Studies, New York, New York, USA
Department of Earth and Environmental Sciences, Columbia University, New York, New York, USA
Center for Meteorology, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA
NASA Goddard Institute for Space Studies, New York, New York, USA
Center for Meteorology, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA
SGT Incorporated, New York, New York, USA
Department of Earth and Environmental Sciences, Columbia University, New York, New York, USA
NASA Langley Research Center, Hampton, Virginia, USA
NASA Langley Research Center, Hampton, Virginia, USA
SGT Incorporated, New York, New York, USA
Columbia University Earth Institute, New York, New York, USA
We use a global climate model to compare the effectiveness of many climate forcing agents for producing climate change. We find a substantial range in the “efficacy” of different forcings, where the efficacy is the global temperature response per unit forcing relative to the response to CO2 forcing. Anthropogenic CH4 has efficacy ∼110%, which increases to ∼145% when its indirect effects on stratospheric H2O and tropospheric O3 are included, yielding an effective climate forcing of ∼0.8 W/m2 for the period 1750–2000 and making CH4 the largest anthropogenic climate forcing other than CO2. Black carbon (BC) aerosols from biomass burning have a calculated efficacy ∼58%, while fossil fuel BC has an efficacy ∼78%. Accounting for forcing efficacies and for indirect effects via snow albedo and cloud changes, we find that fossil fuel soot, defined as BC + OC (organic carbon), has a net positive forcing while biomass burning BC + OC has a negative forcing. We show that replacement of the traditional instantaneous and adjusted forcings, Fi and Fa, with an easily computed alternative, Fs, yields a better predictor of climate change, i.e., its efficacies are closer to unity. Fs is inferred from flux and temperature changes in a fixed-ocean model run. There is remarkable congruence in the spatial distribution of climate change, normalized to the same forcing Fs, for most climate forcing agents, suggesting that the global forcing has more relevance to regional climate change than may have been anticipated. Increasing greenhouse gases intensify the Hadley circulation in our model, increasing rainfall in the Intertropical Convergence Zone (ITCZ), Eastern United States, and East Asia, while intensifying dry conditions in the subtropics including the Southwest United States, the Mediterranean region, the Middle East, and an expanding Sahel. These features survive in model simulations that use all estimated forcings for the period 1880–2000. Responses to localized forcings, such as land use change and heavy regional concentrations of BC aerosols, include more specific regional characteristics. We suggest that anthropogenic tropospheric O3 and the BC snow albedo effect contribute substantially to rapid warming and sea ice loss in the Arctic. As a complement to a priori forcings, such as Fi, Fa, and Fs, we tabulate the a posteriori effective forcing, Fe, which is the product of the forcing and its efficacy. Fe requires calculation of the climate response and introduces greater model dependence, but once it is calculated for a given amount of a forcing agent it provides a good prediction of the response to other forcing amounts.
Received 7 January 2005; accepted 27 June 2005; published 28 September 2005.
Citation: (2005), Efficacy of climate forcings, J. Geophys. Res., 110, D18104, doi:10.1029/2005JD005776.
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