Introduction

As discussed in Chapter 1, climate feedbacks are an integral aspect of the climate system. This chapter investigates the importance of cloud feedbacks. Although many of the best-known early climate models used prescribed clouds (e.g., Manabe and Bryan, 1969), the importance of potential changes in cloudiness for the problem of climate change has been recognized as a key factor since the 1970s (e.g., Arakawa, 1975; Charney et al., 1979). In particular, it is now widely appreciated that “cloud feedback” is a key source of uncertainty limiting the reliability of simulations of anthropogenic climate change (e.g., Houghton et al., 1990).

Nevertheless the whole concept of cloud feedback continues to be obscure, in part because the term “cloud feedback” is often used without being properly defined at all, and is rarely given a definition precise enough to show how it can be quantitatively measured. Further confusion arises from the fact that there are in fact many types of cloud feedbacks (e.g., Schneider, 1972; Schlesinger, 1985; 1988; 1989; Wielicki et al., 1995). In addition, it is widely perceived that existing atmospheric general circulation models (AGCMs) are incapable of making quantitatively realistic simulations of cloudiness.

The purposes of this chapter are to give a definition of cloud feedback, to discuss some particular types of cloud feedback, and to assess the prospects for simulations of cloud feedback on anthropogenic climate change.