Why is the global warming proceeding much slower than expected?

Abstract

Upper air observations from radiosondes and microwave satellite instruments do not indicate any global warming during the last 19 years in contrary to surface measurements where a warming trend is supposedly being found. This result is somewhat difficult to reconcile, since climate model experiments do indicate a reverse trend, namely that upper tropospheric air should warm faster than the surface. To contribute towards an understanding of this difficulty, we have here undertaken some specific experiments to study the effect on climate due to the decrease in stratospheric ozone and the Mt. Pinatubo eruption in 1991. The associated forcing was added to the forcing from greenhouse gases, sulfate aerosols (direct and indirect effect) and tropospheric ozone, which was investigated in a separate series of experiments. Furthermore, we have undertaken an ensemble study in order to explore the natural variability of an advanced climate model exposed to such a forcing over 19 years. The result shows that the reduction of stratospheric ozone does not only cool the lower stratosphere but also the troposphere, in particular the upper and middle part. In the upper troposphere the cooling from stratospheric ozone leads to a significant reduction of the greenhouse warming. The stratospheric aerosols from Mt. Pinatubo generate a climate response (stratospheric warming and tropospheric cooling) in good agreement with microwave satellite measurements. Finally, the analysis of a series of experiments with both stratospheric ozone and the Mt. Pinatubo effect shows a considerably variability in its climate response49 refs.SIGLEAvailable from TIB Hannover: RR 1347(256) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman