On the scattering greenhouse effect of CO₂ ice clouds

The authors offer some remarks on the greenhouse effect due to high clouds that reflect thermal infrared radiation, but do not absorb or emit it. Such clouds are an idealization of the CO₂ ice clouds that are thought to have existed early in the history of Mars. Clouds of this type enter also in the ability of Earth to recover from a globally glaciated "cold start" and in the determination of habitable zones of planetary systems. A simplified model of cloud optical effects is used to estimate the effect of high CO₂ ice clouds on the planetary radiation budget in the solar and infrared spectrum. tt is argued that the scattering greenhouse effect certainly cancels out a large pan of the cooling effect due to the cloud's visible albedo and in some circumstances may even lead to a net warming as compared to the no-cloud case. Speculative implications for the climate of early Mars are discussed.