Top of atmosphere broadband radiative fluxes derived from satellite measurements exhibit surprisingly large decadal variability in the tropics which appears to be related to changes in cloudiness. Climate models fail to reproduce these changes, even when all of the currently known climate forcing agents are prescribed. The interannual variability and spatial signal of the observed changes are analysed and compared to various configurations of the Hadley Centre climate model. Applying EOF analysis to the spatial patterns of the variability shows that these are dominated by El Ni¿o in both the satellite data and the model. However, the second EOF reveals the pattern due to the observed decadal-scale variation in outgoing longwave radiation (OLR), but this is not captured by the climate model. This suggests that either the model lacks some internal physical process or some additional external forcing that is responsible for the observed changes in OLR.