Slide 23 of 26
Notes:
The foregoing discussion of the ERL and the global heat budget focused upon changes in the out going infra red radiation, assuming that the reflection of solar radiation remained the same. If the global surface temperature does indeed continue to change, it must be anticipated that changes in wind patterns and the distribution of thunderstorms will affect the clouds that are responsible for most of the 30% of solar radiation that is currently reflected back to space. The year to year variability in these patterns is such that so far no systematic trend has reliably been detected. However, even small changes in the amount or distribution of cloudiness could potentially have a large impact on the rate of global warming, so they must be considered.
As will be seen from this and the following slide, any increase in low cloud would have an opposite effect to an increase in high cloud, making accurate simulation of the net particularly difficult. When physical scientists talk about predictions of global average warming over the coming century, the greatest cause of uncertainty beside human behavior is probably our ignorance of how to predict clouds.