The radiative forcing of CO2 and the climate feedback parameter are evaluated in several climate models with slab oceans by regressing the global-mean annual-mean top-of-atmosphere radiative flux against the global-mean annual-mean surface air temperature change Delta-T following a doubling of atmospheric CO2 concentration. The method indicates that in many models there is a significant rapid tropospheric adjustment to CO2 leading to changes in cloud, and reducing the effective radiative forcing, in a way analogous to the indirect and semi-direct effects of aerosol. By contrast, in most models the cloud feedback is small, defined as the part of the change which evolves with Delta-T. Comparison with forcing evaluated by fixing sea surface conditions gives qualitatively similar results for the cloud components of forcing, both globally and locally. Tropospheric adjustment to CO2 may be responsible for some of the model spread in equilibrium climate sensitivity, and could affect time-dependent climate projections.

Full Article: http://www.met.rdg.ac.uk/~jonathan/doc/iq.pdf

Last Updated: 2007-07-30