Observed and modeled evolution of the tropical mean radiation budget at the top of the atmosphere since 1985

We have used satellite-based broadband radiation observations to construct a longterm continuous 1985-2005 record of the radiative budget components at the top of the atmosphere for the tropical region (20 degrees S-20 degrees N). On the basis of the constructed record we have derived the most conservative estimate of their trends. We compared the interannual variability of the net radiative fluxes at the top of the tropical atmosphere with model simulations from the Intergovernmental Panel on Climate Change fourth assessment report (AR4) archive available up to 2000 and showed that most of the models capture the 1991 Mount Pinatubo eruption signal in both its timing and amplitude; however, none of them simulate the observed trends. Further comparison showed that among the "best skilled'' models, which are those that showed the highest value of the correlation in simulating one or all of the observed net, shortwave, and longwave radiative fluxes at the top of the atmosphere, the model with an equilibrium climate sensitivity similar to 3.4 degrees C for the doubling CO2 represents the observed amplifying total feedback effect in the tropical atmosphere better than the models with a climate sensitivity similar to 2.7 degrees C or 4.3 degrees C. This total feedback effect was calculated on the basis of an assumed simplified system of interactions between the near-surface temperature and the net radiation at the top of the atmosphere.