Top-of-atmosphere albedo bias from neglecting three-dimensional
radiative transfer through clouds
Clouds cover on average nearly 70% of Earth’s surface and are important
for the global albedo. The magnitude of the shortwave reflection by
clouds depends on their location, optical properties, and 3D structure.
Earth system models are unable to perform 3D radiative transfer
calculations and thus partially neglect the effect of cloud morphology
on albedo. We show how the resulting radiative flux bias depends on
cloud morphology and solar zenith angle. Using large-eddy simulations to
produce 3D cloud fields, a Monte Carlo code for 3D radiative transfer,
and observations of cloud climatology, we estimate the effect of this
flux bias on global climate. The flux bias is largest at small zenith
angles and for deeper clouds, while the albedo bias is largest (and
negative) for large zenith angles. Globally, the radiative flux bias is
estimated to be 1.6 Wm-2 and locally can be on the order of 5 Wm-2.