Graduate students huddled in the middle of a classroom in the Tang Center are in the midst of a passionate negotiation when Professor John Sterman yells, "Time's up! Give me a number!" Getting no reply, he begins plugging figures into a laptop.

Sterman, Jay W. Forrester Professor of Management and director of the System Dynamics Group, is manipulating a new model for climate change. Input the amount of carbon dioxide emitted by every nation, in billions of tons per year, and the model lays out such environmental impacts as changes in sea level and global surface temperature for the years 2010 through 2100. Sterman had divided the class into three blocs--developed, developing, and less developed nations--and given them five minutes (after a few minutes of discussion within their blocs) to negotiate an agreement on greenhouse-gas emissions. They played hardball, and the five-minute limit expired without an agreement. So Sterman has to resort to figures reflecting "business as usual."