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JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 112, D24S04, doi:10.1029/2007JD008740, 2007

Limits on climate sensitivity derived from recent satellite and surface observations

Petr Chylek

Space and Remote Sensing, Los Alamos National Laboratory, Los Alamos, New Mexico, USA


Ulrike Lohmann

Institute for Atmospheric and Climate Science, ETH Zurich, Zurich, Switzerland


Manvendra Dubey

Earth and Environmental Sciences, Los Alamos National Laboratory, Los Alamos, New Mexico, USA


Michael Mishchenko

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


Ralph Kahn

Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA


Atsumu Ohmura

Institute for Atmospheric and Climate Science, ETH Zurich, Zurich, Switzerland


Abstract

An analysis of satellite and surface measurements of aerosol optical depth suggests that global average of aerosol optical depth has been recently decreasing at the rate of around 0.0014/a. This decrease is nonuniform with the fastest decrease observed over the United States and Europe. The observed rate of decreasing aerosol optical depth produces the top of the atmosphere radiative forcing that is comparable to forcing due to the current rate of increasing atmospheric concentration of carbon dioxide and other greenhouse gases. Consequently, both increasing atmospheric concentration of greenhouse gases and decreasing loading of atmospheric aerosols are major contributors to the top-of-atmosphere radiative forcing. We find that the climate sensitivity is reduced by at least a factor of 2 when direct and indirect effects of decreasing aerosols are included, compared to the case where the radiative forcing is ascribed only to increases in atmospheric concentrations of carbon dioxide. We find the empirical climate sensitivity to be between 0.29 and 0.48 K/Wm−2 when aerosol direct and indirect radiative forcing is included.

Received 2 April 2007; accepted 10 August 2007; published 13 December 2007.

Keywords: climate sensitivity; global warming; aerosols.

Index Terms: 3305 Atmospheric Processes: Climate change and variability (1616, 1635, 3309, 4215, 4513); 3359 Atmospheric Processes: Radiative processes; 3367 Atmospheric Processes: Theoretical modeling; 1616 Global Change: Climate variability (1635, 3305, 3309, 4215, 4513); 1699 Global Change: General or miscellaneous.

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Citation: Chylek, P., U. Lohmann, M. Dubey, M. Mishchenko, R. Kahn, and A. Ohmura (2007), Limits on climate sensitivity derived from recent satellite and surface observations, J. Geophys. Res., 112, D24S04, doi:10.1029/2007JD008740.