The wide variety of topics reviewed in this paper show the rapid expansion of cloud physics into strategic and applied areas of research. While good progress has been made in understanding Polar Stratospheric Clouds and their role in depleting ozone, the role of CCN in climate, radiative transfer through clouds, and the initiation of ice in clouds, more work remains to be done in order to resolve some of the outstanding issues in these areas. Ice initiation is a fundamental problem that has still not been solved, and merits continued attention as also suggested by Cooper [1991] in his review of theoretical and observational cloud physics. Another important area for continued research is the effect of ice particle shape on radiative transfer through clouds. Both climate predictions and remote sensing of rain by satellite depend on accurate predictions of the effects of ice on both IR and visible radiation. Further observational studies of PSC's are also needed in order to resolve some of the outstanding questions concerning the type and phase of the cloud particles involved in the destruction of ozone. The role of DMS in producing CCN is still not resolved, and requires more study. The effect of anthropogenically produced CCN on climate is currently not well understood and will clearly receive increased attention in future years.
As shown in this review, clouds and precipitation play an important role in many of the ``strategic'' and applied environmental problems facing our society. While significant progress was made during 1991-1994, successful resolution of these problems will require continued focus on the physics of clouds and precipitation in future years.
Acknowledgments. I would like to acknowledge Carol Makowski for typing this manuscript and Steve Nelson, Roger Pielke, and two anonymous reviewers for their helpful comments.