This is not a topic that I follow, but I was intrigued by some comments in a poster by Penner and Andronova, both leaders in their field, and spent some time at this poster. The abstract stated:
A transient change in the balance between the incoming and outgoing radiation is an important indicator of the changing Earth’s climate. In this paper we use available data from satellites (1980 to present) and ground measurements (1995 to present) to reconstruct the long-term evolution of the energy budget of the tropical atmosphere (20S-20N). We compare the estimate of the radiative budget with the corresponding estimates obtained from model simulations from the AR4 database. We show that in spite of the dramatic increase in the model’s ability to simulate past and recent temperature change, the models show different sensitivities to the Mt. Pinatubo eruption and do not agree with observations of the overall radiative balance tendencies over 1980-2000.
First, they spliced and interpolated the available instrumental records for outgoing longwave radiation and shortwave radiation at the TOA in the tropiocs (20S-20N) (ERBE, CERES).
They then examined trends at TOA reporting:
They reported that Pinatubo is represented well in “some” models, but that the El Nino-La Nina effect is poorly represented, as they miss the decrease in reflected radiation.
They report that the total (diffused plus direct) solar radiation 1994-2006 from the World Radiation Data Center shows an overall positive trend of ~1.5 wm-2, which they say is consistent with the small negative trend in outgoing SW at the TOA, since less reflection would mean that more radiation would reach the surface, noting in particular that the total increase can be attributed to the Australia-Fiji area.
Their conclusions are that:
While I noted at the top that I’m not familiar with the issues in this area in detail, these results seemed interesting in that they seem to reconcile the failure of the tropical troposphere to warm at a greater pace than the tropical surface. I presume that the decreased reflectiveness of the tropical atmosphere is unrelated to GHGs but might have something to do with aerosols or clouds or both. This also doesn’t contradict prior masking of GHG effects by aerosol effects.
However, the changes described here by Penner and Andronova are large ones and they seem like the sort of thing that should be got right by models being used for policy.