Stratosphere adjusted radiative forcing calculations in a comprehensive climate model

A new technical procedure is introduced to determine the stratosphere adjus ted radiative forcing at the tropopause in the framework; of the 3-D climat e model ECHAM4. However, the procedure appears to be appropriate for other GCMs as well. it allows to study in a straightforward way the problem of th e general usefulness of radiative forcing as a reliable predictor of climat e change. Some examples are given for illustration. It is, once again, conf irmed that the climate sensitivity is practically equal for experiments wit h increased solar insolation and increased CO2 concentration. However, a hi gher climate sensitivity is obtained for ozone perturbations with a horizon tally or vertically inhomogeneous distribution. The latter finding is in qu alitative agreement with respective results reported in other studies, wher eas the value of the climate sensitivity is exceptionally high in our model . The physical reasons for the unique model behaviour in the ozone experime nts are currently not understood.