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Published Online June 18, 2009
Science DOI: 10.1126/science.1174461

Reports

Submitted on April 3, 2009
Accepted on May 22, 2009

Consistency Between Satellite-Derived and Modeled Estimates of the Direct Aerosol Effect

Gunnar Myhre 1*

1 Center for International Climate and Environmental Research–Oslo (CICERO), Post Office Box 1129 Blindern, N-0318 Oslo, Norway.

* To whom correspondence should be addressed.
Gunnar Myhre , E-mail: gunnar.myhre{at}cicero.uio.no

The direct aerosol effect has a radiative forcing estimate of –0.5 Wm–2 in the IPCC AR4, offsetting the warming from CO2 by almost one-third. The uncertainty range, however, ranges from –0.9 to –0.1 Wm–2, largely due to differences between estimates from global aerosol models and observation-based estimates, with the latter tending to have stronger (more negative) radiative forcing. This study demonstrates consistency between a global aerosol model and adjustment to an observational-based method, giving a global and annual mean radiative forcing weaker than –0.5 Wm–2 with a best estimate of –0.3 Wm–2. The physical explanation for the earlier discrepancy is that the relative increase in anthropogenic black carbon (absorbing aerosols) is much larger than the overall increase in the anthropogenic abundance of aerosols.


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Science. ISSN 0036-8075 (print), 1095-9203 (online)