  Carbon dioxide ice clouds are thought to play an important role for cold
terrestrial planets with thick CO2 dominated atmospheres. Various previous
studies showed that a scattering greenhouse effect by carbon dioxide ice clouds
could result in a massive warming of the planetary surface. However, all of
these studies only employed simplified two-stream radiative transfer schemes to
describe the anisotropic scattering. Using accurate radiative transfer models
with a general discrete ordinate method, this study revisits this important
effect and shows that the positive climatic impact of carbon dioxide clouds was
strongly overestimated in the past. The revised scattering greenhouse effect
can have important implications for the early Mars, but also for planets like
the early Earth or the position of the outer boundary of the habitable zone.
