Causes of the reduction in uncertainty in the anthropogenic radiative forcing of climate betweeen IPCC (2001) and IPCC (2007)

The Inter-governmental Panel on Climate Change reviews the best available scientific information on climate change and publishes a report every 5-6 years. The fourth assesment report was released this year and is the IPCC 2007 report. In contrast to the IPCC 2001 report, this report emphasizes with greater confidence that global warming is due to human/anthropogenic activities. Until recently, the sign of the anthropogenic radiative forcing was uncertain largely due to the uncertainty associated with radiative effects (direct and indirect) of atmospheric aerosols. Haywood and Schulz in their recent paper (titled above) inter-compare the probability distribution function of anthropogenic radiative forcing from IPCC 2001 and IPCC 2007 and show that a significant progress has been made in reducing the uncertainty in anthropogenic radiative forcing since IPCC 2001. They conclude that " the single most contributor to this conclusion appears to be the reduction in the uncertainty associated with the aerosol direct effect, followed by the provision of a best estimate for the aerosol cloud albedo indirect effect ".

References :

Haywood, J. M., and M. Schulz (2007), Causes of the reduction in uncertainty in the anthropogenic radiative forcing of climate between IPCC (2001) and IPCC (2007), Geophys. Res. Lett., doi:10.1029/2007GL030749, in press.

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