Richard C. J. Somerville
Catherine Gautier
Co Chairs

The Aspen Global Change Institute (AGCI) devoted its first of three 1994 summer science sessions to the topic of climate-radiation feedbacks and the credibility of atmospheric models. This summer institute took place at the AGCI headquarters in Aspen, Colorado from July 10 to July 23, 1994. Twenty-five scientists participated, including three graduate students, a few young postdoctoral researchers, and a preponderance of senior people. Nearly all of the group stayed for the full two weeks.

The topic was picked because of its scientific importance and timeliness. Cloud-radiation interactions have long ranked as one of the most critical areas in global change research. In particular, when climate models are intercompared, cloud-radiation parameterizations are responsible for most of the global-mean differences in sensitivity to greenhouse gas increases. The uncertainty in model responses is directly due to a lack of fundamental understanding of the physical processes involved. A major research effort is underway worldwide in response to this challenge. As one prominent example, the Atmospheric Radiation Measurement (ARM) Program, the flagship global change effort of the U. S. Department of Energy, has been undertaken in response to this pressing scientific need. Furthermore, closely related research areas, such as the role of atmospheric aerosols in climate, are also beginning to receive the attention they deserve. We felt that the time was ripe to devote a two-week AGCI summer session to this general area, with a format designed to encourage a thorough examination of the key scientific issues, something that is impossible at a typical research meeting which lasts a few days and is made up of many short talks.

This AGCI session was an invitational meeting, with the participants chosen to ensure that a broad range of relevant topics was covered. The represented areas of expertise included climate modeling, satellite remote sensing, in situ measurements, theoretical dynamics, radiation, and cloud physics, among others. Several of the group were actively involved in general circulation model (GCM) research, especially developing parameterizations for GCMs. Several of the group were involved in major field programs, such as ARM, CEPEX and COARE. Although we had considered inviting a few representatives of the policymakers who are most interested in climate and global change, we ended up not having any people from the policy world. Thus, essentially all the expertise of the participants was in various aspects of the physical climate system.

We had written in advance to the participants, asking them each to give a talk, for about an hour, on a topic of their choice. Typically, the topic was on some aspect of their own recent research related to the general subject area of cloud-radiation interactions and closely allied fields. We suggested to each invitee that it would be especially interesting to hear about new work, work in progress, and thoughts on important directions for future work. We advised them that their audience would be the group of all the other participants, so that the general level of the talk should be that of a research seminar.

We did not require the speakers to provide any advance write-up of their talk, or even a title. We wanted to encourage spontaneity, and we especially wanted the participants to talk about their current research interests, rather than to report on work which they might have already finished, or even published. We did ask participants to feel free to bring reprints and preprints with them, however, and AGCI photocopied and distributed a considerable amount of this kind of material, together with copies of the transparencies used in each of the talks.

We scheduled two or three of these lectures on each of the ten weekday mornings, so it was possible to accommodate all the participants, even allowing generous time for discussion. Because the discussions were spirited, many of the talks lasted far beyond the one-hour limit. Those who wished to give more than one talk were encouraged to do that too. During the afternoons, several specialized discussion groups formed around topics which the participants themselves selected. In addition, we held impromptu tutorials on GCMs and on fractals and multi-fractals, in which experts in these areas provided background material for the research talks. We also held wrap-up sessions at the end of each of the two weeks, in which we tried to summarize our progress and identify key issues for further attention. Finally, we held two public lectures, open to the Aspen community.

The speakers worked with writer-editors to produce a summary of each talk, including figures and references as appropriate. Edited versions of these summaries make up this report of the meeting.

When good scientists are brought together for two weeks in a pleasant and unstructured environment with few distractions, then worthwhile scientific interactions occur spontaneously. Every working scientist knows that new ideas and new research collaborations often spring from such meetings, and they were among the most valuable products of this AGCI session. Our goal was simply that at the end of the two weeks, the participants should feel that the experience had been intellectually worthwhile and that the seeds of some promising research had been sown. This goal was certainly met at this AGCI session.