For years, Ronald Prinn, ScD ‘71, had watched policymakers’ eyes glaze over when he presented them with alarming evidence of human-caused climate change. So naturally, the professor of atmospheric science was pleasantly surprised when he learned in October that the Intergovernmental Panel on Climate Change would share the 2007 Nobel Peace Prize with Al Gore for documenting and raising awareness of global warming.

The recognition of climate change as a vital problem has been a long time coming. But action is finally being taken, thanks to the many scientists who have spent years gathering and interpreting data–and publicizing its significance. That action includes a new push by members of the U.S. Congress to pass legislation aimed at curbing greenhouse-gas emissions.

As director of MIT’s Center for Global Change Science, Prinn has played a key role in bringing climate change to the public’s attention. His Advanced Global Atmospheric Gases Experiment (AGAGE) is cele­brating its 30th year of monitoring ozone-­depleting compounds (including the chlorofluorocarbons once widely used in aerosols) and greenhouse gases like methane. And a program that he founded in 1991 with Sloan School professor Henry Jacoby, an economist, has brought physical and social scientists into unusually close, ongoing collaboration with environmentalists to create climate models that account for the human causes and costs of global warming. They’re also trying to figure out what must be done to mitigate or stop it. An early advocate of incorporating science into public ­policy, Prinn has testified before Congress and served as a lead author on the Nobel Prize-winning climate panel’s 2007 report.

When he and Jacoby started the modeling project, Prinn says, they faced basic questions: “Could we ever credibly forecast climate?” And what was the best way to factor in human activity? Some colleagues “thought it was crazy” to tackle so complex a task, Prinn recalls. Even he considered the undertaking quixotic. But to him, it was a moral duty. “If you’re getting funding to study planet Earth, and you can help decision-making, you ought to do it,” he insists.

“The thing that’s unusual about Ron in relation to many other scientists,” says Jacoby, “[is that] from the earliest, he understood that the science, to be truly useful, needed to be integrated with the public policy, and he was willing to devote time and energy to that aspect of the work. There are many good scientists in the world. But not many of them are good at that kind of collaborative work.”

Prinn has watched his colleagues come around to the idea of modeling that includes inputs from many areas of research, including the social sciences. And he’s seen the public become concerned about the global warming predicted by those models. “It’s been interesting to see the evolution,” he says.

When Prinn was a graduate student at MIT in the late 1960s, only a few scientists in the world were studying the chemistry of Earth’s atmosphere. The space program was in its infancy, and Prinn earned his chemistry doctorate investigating the atmospheres of other planets: the composition of Jupiter’s clouds, the photo­chemistry of Venus. He was appointed an assistant professor in meteorology at MIT around the time he defended his thesis in 1971.

What sharpened his interest in the atmosphere of our own planet, he says, was his work in the 1970s modeling the environmental impact of Boeing’s proposed supersonic aircraft. In order to surpass the speed of sound, the Boeing 2707 would have flown through the thin air of the ozone layer. But the engines would have produced nitric oxide, which chemists knew destroys ozone. Prinn and other MIT researchers set up a computer simulation demonstrating the risks that a fleet of supersonic aircraft would pose to the ozone layer, which protects the planet from the sun’s ultraviolet radiation. Plans to build the fleet were eventually scrapped for a variety of reasons, but the work stayed with him. “I got interested in atmospheric chemistry on Earth,” he says.

In 1974, future Nobel laureates Sherwood Rowland and Mario Molina (who would become an MIT professor) published their seminal work describing how the inert chlorofluorocarbons (CFCs) widely used in refrigeration systems and spray cans could reach the ozone layer, where ultraviolet radiation might dislodge highly reactive chlorine molecules that could catalyze the decomposition of ozone. At the time, however, Rowland and Molina had no direct evidence that this was happening. Their work left chemists with a feeling of alarm: so little was known about the chemistry of the atmosphere, and in particular about the effects of man-made gases on it. No one knew what the life cycle of these gases might be–or whether the ozone layer was in fact breaking down. Did CFCs really persist in the atmosphere and travel into the ozone layer? How were naturally occurring, highly reactive chemicals called hydroxyl radicals interacting with the man-made emissions?

These questions spurred Prinn to launch, in 1978, a large-scale project to measure and model the chemistry of Earth’s atmosphere. AGAGE continuously monitors the emission rate and the persistence of 45 ozone-depleting and greenhouse gases, including CFCs, hydroxyl radicals, methane, and nitrous oxide. It also measures global levels of all the gases regulated under the Kyoto and Montreal Protocols (except carbon dioxide, which is monitored by a U.S. government agency). Findings from the project’s detectors at five coastal sites around the world show the regional distribution of these gases and allow researchers and governments to monitor where they originate and where they go. Results are posted online.

“Back in the 1960s, regional air pollution was the major interest in atmospheric monitoring and science; global monitoring was really the field of only a few scientists,” recalls Paul Fraser, who leads the changing-atmosphere research group at Australia’s national science agency, the Commonwealth Scientific and Industrial Research Organisation. (One of those few was Caltech’s Charles Keeling, who had begun continuous monitoring of atmospheric carbon dioxide levels in Mauna Loa, HI, in 1958.)

“Ron’s big contribution was to expand the idea that we had to look at the Earth globally, not only for CO₂ but for all the gases important for climate change and ozone depletion,” says Fraser. “That was a big change of emphasis in where the exciting science was being done. His work has led to a major expansion in the effort of research agencies around the world in studying the global problem as well as maintaining regional pollution studies.”

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.

Since 1999, Prinn, Jacoby, and their collaborators have published many scientific papers based on the model’s predictions. And to get the word out to the public and to lawmakers, they made a pair of gambling wheels to represent the probabilities of a range of temperature increases over the next hundred years. Like upright versions of the wheel used on Wheel of Fortune, each is a spinning pie chart. One wheel assumes no policy change, and the other assumes that the Kyoto Protocol–which calls for reducing emissions of carbon dioxide and five other greenhouse gases–is implemented by 2010 by all the countries that originally agreed to it. It also assumes adoption of more aggressive policies that lower global greenhouse-gas emissions to less than double their preindustrial levels by 2100. (See “Which Wheel Would You Rather Spin?” opposite.)

In public speeches, Prinn demonstrates the two wheels and asks how much the audience, given $100,000 to gamble, would pay for an energy policy that let them spin the one with the more favorable outcomes. The answer, he says, tends to be around $10,000. The cash is entirely hypothetical, of course, but Prinn says his informal surveys reveal that the public is willing to invest money in the short term in order to lower the risk of disastrous climate change. And the investment required could turn out to be surprisingly small. According to a British study completed last year, implementing policies that mitigate climate change would cost just 1 percent of the global gross domestic product.

“People are used to dealing with uncertainty,” says Prinn. “They are used to thinking about changing their habits and paying for something even when they know the outcome they want is not guaranteed.” For example, a patient informed of a heart-attack risk 50 percent above average is unlikely to refuse to pay for cholesterol medication just because a particular life expectancy can’t be promised.

Right now, says Prinn, “the computers are purring away, working full time to do a new set of calculations�� that incorporate new findings about, among other things, the oceans’ ability to absorb heat. The oceans slow down warming, “but not as much as we thought,” he says. “It would have been wonderful if the science had concluded it’s not such a bad situation, but that’s the nature of our research. We let the results fall where they may.” The MIT scientists are now redoing the wheels to depict a more urgent situation.

Prinn is convinced that the United States can’t wait any longer to mitigate climate change, and he harbors only cautious optimism that it will act quickly enough. “I have a wait-and-hope-and-see attitude about what [policy changes] might happen to address this issue,” he says. “Energy security is looming [larger and larger]. These are issues liberals and conservatives are concerned about.” Within academia, “the students are driving change,” he says. “Young people are not climate skeptics.”

Which Wheel Would You Rather Spin?
Betting how hot the planet will get if we do­­–or don’t–cap greenhouse-gas emissions.

The MIT Joint Program on the Science and Policy of Global Change created a pair of spinning gambling wheels to demonstrate the potential impact of policies designed to mitigate global warming. Program researchers estimated the probability of negligible, moderate, and dramatic global average temperature increases between 1990 and 2100 if the original signers of the Kyoto Protocol (including the U.S.) enact its provisions by 2010 or earlier and implement even more stringent policies lowering emissions to less than double their preindustrial levels by 2100. They also calculated the probabilities assuming no policy change and created pie charts showing the likelihood of various global temperature increases under both scenarios. (Each piece of pie represents a range of temperature ­increases; its size reflects its probability.)

The “no cap” wheel has only a sliver representing a temperature increase of less than 1 ºC; if the wheel is spun, there’s just a 4.1 percent probability (1 chance in 24) that it will stop there. The odds of landing on the wedge showing an increase greater than 5 ºC are about 1 in 26, or 3.8 percent.

In the “cap” scenario, milder warming is more probable; the two largest temperature increases from the “no cap” wheel are not included. The largest increase, greater than 3 ºC, represents odds of about 1 in 29, or 3.5 percent. The odds of milder increases are much better: 1 in 6, or 15.8 percent, for less than 1 ºC and 36 percent for between 1 and 1.5 ºC.

Both wheels are due for sobering revisions, however, in view of new findings that oceans don’t slow global warming as much as previously thought.