Tropopause-height feedback and radiative forcing in 2D climate simulations

L. DELOBBE, C. TRICOT, J. P. VAN YPERSELE

Abstract

The climate response of the Northern Hemisphere to the anthropogenic greenhouse gas forcing is studied with a zonally-averaged climate model. First, a simple method is proposed to improve the radiative forcing in climate models with a low vertical resolution for the atmospheric dynamics. Then, the sensitivity of the model response to tropopause height parameterization is examined. It is shown that small changes in tropopause height induced by climate warming introduce an important feedback which strongly affects the 2 x CO2 sensitivity at equilibrium. Finally, transient climate evolution is simulated for the time-dependent radiative forcings corresponding to the scenarios BaU and D of the IPCC 1990. The contributions of various greenhouse gases are taken into account with an effective-CO2 method whose validity is shortly discussed. Several transient simulations have been undertaken with different tropopause height parameterizations. The results show further that the potential tropopause-height feedback can significantly influence the model response.

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