Forum on Global Change Modeling



On October 12-13, 1994, a Forum on Global Change Modeling was held at the invitation of the Subcommittee on Global Change Research (SGCR) to help address requests from the White House Office of Science and Technology Policy (OSTP) and from Congressman Dingell to the General Accounting Office (GAO). The Forum labored to produce a consensus document and to provide the GAO representatives a sense of the debate on issues related to the use of climate models to inform policy. The charge to the panel and the report are attached [see caveat].

The invited participants included Eric Barron (chair), Joyce Penner, Chuck Hakkarinen, Dan Lashof, Jerry Mahlman, Pat Michaels, Roy Jenne, Richard Lindzen, Tamara Ledley, and Tom Wigley; a number of additional scientists were invited, but were only able to submit written comments. In addition, Mike MacCracken, Ken Bergman, Jay Fein, Mike Riches, Lowell Smith, Richard Poore, Robert Schiffer, Dave Goodrich, Courtney Riordan, Ghassem Asrar, Robert Watson, Tony Janetos, Rick Piltz, and Scott Sandgathe participated as agency, congressional, and OSTP representatives.

The report has been positively reviewed by a wider segment of the climate community. Still, the forum participants believe that this report is just a beginning. It includes the judgment of participating experts and reviewers-as opposed to detailed arguments-on the credibility of climate model projections. As an additional step, the community needs to take the next step of elucidating fully the reasons models make the predictions that they do. This effort should be a significant part of a rational approach to determine whether models are behaving reliably. One aspect of this extended process is the thorough international assessment that is being conducted by the Intergovernmental Panel on Climate Change (IPCC), which is due to be published in late 1995. Forum Charge

The charge to those attending the Forum and to those who submitted written comments was to develop a brief statement on the credibility of projections of climate change provided by General Circulation Models (GCMs) as background for potential interpretation of model results in the context of developing and considering national policy options. The focus of this effort was specifically on the climate aspects of the entire global change issue (figure 1) - thus not on the emission scenarios, the consequences of change to ecosystems and natural resource systems, or the socio-economic implications and potential for responses.

Working Objective Formulated by Forum Participants

The attendees at the Forum decided to develop an ordered list of statements from "virtually certain" to "uncertain" that summarizes the major findings and implications stemming from climate system model experiments (most commonly with GCMs) and the issues being debated in the scientific literature, and to express these statements in terms that indicate their potential policy relevance. The participants agreed to include with each ranked statement the basis for the consensus view. In addition, the participants at the Forum agreed to provide indications of where opportunities exist for early progress in reducing uncertainties and improving confidence in model projections. The report that follows consists of three parts. First, a number of conclusions are identified as "virtually certain," based on observations, experiments, and models. These conclusions provide a significant starting point for discussion, yet they do not directly stem from climate system model experiments. These statements are provided in Part 1 as an introduction. Second, Part 2 provides the ranked statements that refer to model experiments and predictions. Finally, a list of opportunities for early progress in reducing uncertainties is given in Part 3.

To Go to Part 1. Introduction