SINOPSIS

A pair of papers recently published in Science have shown there is more absorption of solar radiation than estimated by current atmospheric general circulation models (GCMs), and that the discrepancy is associated with cloudy scenes.
We have devised a simple model showing how fields of broken clouds cause average photon path lengths to be greater than those predicted by homogeneous radiative transfer calculations of cloud/atmosphere ensemble with similar albedos, especially under and within the cloud layer. This one-sided bias is a contribution to the anomalous absorption. This model has been described by us previously and is reviewed here for clarity. We illustrate the model quantitatively with a numerical stochastic radiative transfer calculation. More than half the anomaly is explained, for the parameters used in the numerical example.