Cloud feedback examined using a two-component time-dependent climate model

A zero-dimensional, time-dependent, two-component atmosphere-ocean climate model is used to investigate the influence of the primary climate feedbacks on the steady-state and time-dependent behaviour of the climate system. The model results show that water vapor and snow-ice albedo feedbacks may lead to multiple stable equilibria. We divide cloud feedback into three components arising from: cloud water content, cloud altitude and cloud amount. A sensitivity study shows that depending on the rate of change of cloud infrared emissivity and cloud albedo with temperature, several regimes with differing stability characteristics may be identified. In the model, the cloud water content and cloud altitude feedbacks, coupled with enhanced greenhouse longwave forcing, lead to the formation of a new warm stable equilibrium. In a time-dependent simulation with a single layer ocean, the global mean surface temperature rises gradually, then rapidly, finally reaching a value approximately 14 K warmer than at present, when an enhanced greenhouse flux of 4 Wm −2 is added. The model also suggests that, without additional short-wave or long-wave forcing, the cloud amount feedback may lead to free oscillations with a period of several years. When a weak annual solar forcing is imposed, these oscillations become chaotic