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The Top-of-the-Atmosphere Radiation Budget: Model Simulations vs. Direct Measurements over the Tropics
Reference
Andronova, N., Penner, J.E. and Wong, T. 2009. Observed and modeled evolution of the tropical mean radiation budget at the top of the atmosphere since 1985. Journal of Geophysical Research 114: 10.1029/2008JD011560.

What was done
The authors "used satellite-based broadband radiation observations to construct a long-term continuous 1985-2005 record of the radiative budget components at the top of the atmosphere (TOA) for the tropical region (20S-20N)," after which they (1) "derived the most conservative estimate of their trends" and (2) "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."

What was learned
First of all, the three researchers report that "the tropical system became both less reflective and more absorbing at the TOA," and that "combined with a reduction in total cloudiness (Norris, 2007), this would mean that the tropical atmosphere had recently become more transparent to incoming solar radiation, which would allow more shortwave energy to reach earth's surface." Secondly, they found that "none of the models simulates the overall 'net radiative heating' signature of the earth's radiative budget over the time period from 1985-2000."

What it means
With respect to the first of their findings, and the associated finding of Norris (2007), Andronova et al. state that these observations "are consistent with the observed near-surface temperature increase in recent years," which provides an independent validation of the TOA radiation measurements. With respect to their second finding, however, the failure of all of the AR4 climate models to adequately simulate the TOA radiation measurements basically discredits the models; and it reveals the irrationality of using them to inform international policy with regard to the need (or non-need) to regulate anthropogenic CO2 emissions. And the combination of these two conclusions suggests that the historical rise in the air's CO2 content has likely played a next-to-negligible role in the post-Little Ice Age warming of the world.

Reference
Norris, J.R. 2007. Observed interdecadal changes in cloudiness: Real or spurious? In: Broennimann, S. et al. (Eds.) Climate Variability and Extremes During the Past 100 Years. Springer, New York, New York, USA, pp. 169-178.

Reviewed 28 October 2009