Graeme L. Stephens is a professor in the Department of Atmospheric Sciences at Colorado State University. His research interests include the use of remote sensing to study the Earth’s climate with emphasis on clouds and radiation. Currently he is the principal investigator of NASA's CloudSat mission, which is designed to probe clouds providing the kinds of information illustrated in Figure 5 of this article. Address: Department of Atmospheric Sciences, Colorado State University, Ft. Collins, CO 80253. Internet: stephens@atmos.colostate.edu http://cloudsat.atmos.colostate.edu