Efficacy of climate forcings

doi:doi:10.1029/2005JD005776

Abstract

Cited By (155)

Abstract

JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 110, D18104, 45 PP., 2005
doi:10.1029/2005JD005776

Efficacy of climate forcings

J. Hansen

NASA Goddard Institute for Space Studies, New York, New York, USA

Columbia University Earth Institute, New York, New York, USA

M. Sato

Columbia University Earth Institute, New York, New York, USA

R. Ruedy

SGT Incorporated, New York, New York, USA

L. Nazarenko

Columbia University Earth Institute, New York, New York, USA

A. Lacis

NASA Goddard Institute for Space Studies, New York, New York, USA

Department of Earth and Environmental Sciences, Columbia University, New York, New York, USA

G. A. Schmidt

NASA Goddard Institute for Space Studies, New York, New York, USA

Department of Earth and Environmental Sciences, Columbia University, New York, New York, USA

G. Russell

NASA Goddard Institute for Space Studies, New York, New York, USA

I. Aleinov

Columbia University Earth Institute, New York, New York, USA

M. Bauer

Columbia University Earth Institute, New York, New York, USA

S. Bauer

Columbia University Earth Institute, New York, New York, USA

N. Bell

Columbia University Earth Institute, New York, New York, USA

B. Cairns

Department of Applied Physics and Applied Mathematics, Columbia University, New York, New York, USA

V. Canuto

NASA Goddard Institute for Space Studies, New York, New York, USA

M. Chandler

Columbia University Earth Institute, New York, New York, USA

Y. Cheng

SGT Incorporated, New York, New York, USA

A. Del Genio

NASA Goddard Institute for Space Studies, New York, New York, USA

Department of Earth and Environmental Sciences, Columbia University, New York, New York, USA

G. Faluvegi

Columbia University Earth Institute, New York, New York, USA

E. Fleming

NASA Goddard Space Flight Center, Greenbelt, Maryland, USA

A. Friend

Laboratoire des Sciences du Climat et de l'Environnement, Orme des Merisiers, Gif-sur-Yvette, France

T. Hall

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

C. Jackman

NASA Goddard Space Flight Center, Greenbelt, Maryland, USA

M. Kelley

Laboratoire des Sciences du Climat et de l'Environnement, Orme des Merisiers, Gif-sur-Yvette, France

N. Kiang

NASA Goddard Institute for Space Studies, New York, New York, USA

D. Koch

Columbia University Earth Institute, New York, New York, USA

Department of Geology, Yale University, New Haven, Connecticut, USA

J. Lean

Naval Research Laboratory, Washington, D. C., USA

J. Lerner

Columbia University Earth Institute, New York, New York, USA

K. Lo

SGT Incorporated, New York, New York, USA

S. Menon

Lawrence Berkeley National Laboratory, Berkeley, California, USA

R. Miller

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

P. Minnis

NASA Langley Research Center, Hampton, Virginia, USA

T. Novakov

Lawrence Berkeley National Laboratory, Berkeley, California, USA

V. Oinas

SGT Incorporated, New York, New York, USA

Ja. Perlwitz

Department of Applied Physics and Applied Mathematics, Columbia University, New York, New York, USA

Ju. Perlwitz

Columbia University Earth Institute, New York, New York, USA

D. Rind

NASA Goddard Institute for Space Studies, New York, New York, USA

Department of Earth and Environmental Sciences, Columbia University, New York, New York, USA

A. Romanou

NASA Goddard Institute for Space Studies, New York, New York, USA

Department of Earth and Environmental Sciences, Columbia University, New York, New York, USA

D. Shindell

NASA Goddard Institute for Space Studies, New York, New York, USA

Department of Earth and Environmental Sciences, Columbia University, New York, New York, USA

P. Stone

Center for Meteorology, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA

S. Sun

NASA Goddard Institute for Space Studies, New York, New York, USA

Center for Meteorology, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA

N. Tausnev

SGT Incorporated, New York, New York, USA

D. Thresher

Department of Earth and Environmental Sciences, Columbia University, New York, New York, USA

B. Wielicki

NASA Langley Research Center, Hampton, Virginia, USA

T. Wong

NASA Langley Research Center, Hampton, Virginia, USA

M. Yao

SGT Incorporated, New York, New York, USA

S. Zhang

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: Hansen, J., et al. (2005), Efficacy of climate forcings, J. Geophys. Res., 110, D18104, doi:10.1029/2005JD005776.

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