Wheel of Global Fortune

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The chemical industry agreed to fund the AGAGE project for three years, Prinn says, because companies wanted to know how they were affecting the environment. The companies supplied information about production and sales of gases, and by the time the three years were up, the scientists had provided evidence that CFCs indeed persisted for a long time and had the potential to cause serious ozone destruction. The findings were dramatically confirmed in 1985, when a hole was spotted in the ozone layer above Antarctica. "We knew there were rapid increases in these gases and that humans were playing a huge if not exclusive role in ozone depletion and greenhouse-gas emissions," says Prinn. Recognizing the value of monitoring both these long-lived, dangerous chemicals and naturally occurring gases in the atmosphere, NASA took over as the primary funder of the project.

By 1988, the year after the milestone Montreal Protocol began phasing out CFCs in industrial countries, "the climate issue was getting big," says Prinn. It became so big that Prinn no longer had time to continue studying extraterrestrial chemistry: "The planets dropped to one side, and I began to focus on global climate." He and Thomas Jordan, then the head of the earth, atmospheric, and planetary sciences department, started the Center for Global Change Science in 1990 to study how the oceans, land, and atmosphere interact to determine the terrestrial climate.

But the work of the center did not take into account how human activity was contributing to climate change. So in 1991, hoping to combine the work of climate scientists with that of economists and other social scientists, Prinn teamed up with Jacoby to launch the Joint Program on the Science and Policy of Global Change. "At that time, [if you were] a scientist, getting involved in policy might taint you," says Prinn. He suspects that when he started the joint program, "some of my colleagues thought I'd gone off the deep end."

Indeed, the problem they'd taken on was an intricate one. The program's main project is a computer simulation called the MIT Integrated Global Systems Model, which can, among other things, predict the rise in global average temperature over time. It draws on information about variables including world economic growth, world population growth, technological change, emissions of greenhouse gases, and geological, oceanographic, and atmospheric dynamics. The researchers have used the megamodel to assess the potential impact on the planet's temperature of major energy bills being debated in Congress, and to determine the impact of alternative energy technologies on U.S. gross domestic product.

"Climate research is like an orchestra," says Prinn. "To make great music, you need to have all these things playing together." It took five years of rehearsing to integrate economic and climate models into a unified research tool. "We were looking at the whole earth: climate, human health, agriculture, economies," he says. "We knew the predictions would be uncertain, so we decided to give the odds of particular outcomes given particular choices."

Handling uncertainty means "doing hundreds and hundreds of runs of the model with different assumptions," says Prinn. For ex­ample, the model makes assumptions about economic factors such as productivity and innovation to predict industrial emissions of greenhouse gases. The researchers then look at the outcomes and assess how probable--and how dangerous--each might be.