Did you know you're an active contributor to the world's biggest research project? It's called the Great Carbon Dioxide Experiment, and it can be summed up by a simple question: What happens if you double the amount of carbon dioxide in the earth's atmosphere?

Carbon dioxide (CO2) is a naturally occurring gas, constantly being absorbed and re-emitted by various parts of the ecosystem. But CO2 is also given off -- quite unnaturally -- whenever fossil fuels like gasoline, oil, natural gas, or coal are burned by human beings. Every time you step on your car's accelerator or fire up your gas grill to cook some burgers, you're pumping a little additional CO2 into the air. Multiply this by a few billion people, and you're talking about billions of tons of extra CO2 being released each year.

Computer-rendered maps show the hypothetical effects of rising sea levels on the southeast (red areas indicate newly submerged land.) The greenhouse effect influences sea levels in two ways: by increasing the volume of sea water (which expands as it warms) and by melting polar ice.

This experiment is especially compelling because carbon dioxide is far and away the most important of the greenhouse gases. These airborne gases work somewhat like the glass of a greenhouse or the windshield of a car on a sunny day -- letting the sun's rays pass through to hit the earth, then trapping the reflected energy in the form of infrared radiation.

For the most part, this atmospheric blanket is a good thing. Take it away, and the earth's average surface temperature would plunge to around zero degrees Fahrenheit. But make the greenhouse panes thicker (which is essentially what happens every time carbon dioxide is released into the air) and the temperature should theoretically start to creep higher.

How much higher? No one knows for sure. There's general agreement that levels of atmospheric carbon dioxide -- which has a life span of about 70 years -- have climbed 30 percent since 1900 (the end of the so-called preindustrial era). Most policy makers also accept the notion that atmospheric CO2 will rise to twice preindustrial levels by the middle of the next century; last year's international conference on climate change, held in Kyoto, Japan, was based on the premise that a doubling of CO2 levels is inevitable.

The trouble is, no one can say for sure just how all this added carbon dioxide will affect the world's weather. "People want us to tell them exactly how bad global warming will be, and who will be hurt most by it -- but science can't answer those questions," says Jerry Mahlman, director of the National Oceanic and Atmospheric Administration's Geophysical Fluid Dynamics Laboratory, at Princeton. He should know: GFDL -- established in 1955 by an act of Congress and funded entirely by the federal government -- is one of two supercomputer centers in the country capable of spinning out detailed long-range global warming scenarios. In an air-conditioned room on the Forrestal Campus, the lab's Cray T-90 32-processor supercomputer works around the clock, crunching equations at an average rate of 15 billion calculations per second as it models a smorgasbord of natural phenomena -- including hurricanes, holes in the ozone layer, and, most importantly, the future effects of increased greenhouse gases on the earth's climate.

"Since 1900, we've seen an increase in the earth's temperature of about 1.1 degrees Fahrenheit -- with one-quarter of this rise coming in the last three years," says Mahlman. "That increase is simply too great to be explained by the sun's getting brighter or other natural causes ... and it's right in line with what our models predict from the increased carbon dioxide levels."

This upward trend appears to be accelerating. The year 1997 went down as the hottest in recorded history (capping a decade of record-breaking temperatures), and the global average for the first five months of 1998 was a whopping half-degree higher than the 1997 average. The century-long warming spell has also caused the topmost layer of ocean water to heat and expand, apparently forcing the sea level up some six to eight inches over the past 100 years.

And the bad news is, things are only going to get worse. According to GFDL's models, the following projections have a better than 90-percent chance of coming true if and when CO2 levels reach the doubling point:

· We'll experience an additional surface warming of between 2.7 and 8.1 degrees F by the year 2100.

· Sea levels will also rise between one and three feet by 2100 -- and will continue rising steadily for at least another 500 years, as the added warmth works its way down into the ocean's depths.

· As temperatures rise, atmospheric water vapor will increase as well. This extra evaporation will cause precipitation to go up about 1 percent for each degree F of global warming -- but it will also dry out summer soil more rapidly. "Basically, the wet areas will get wetter, and the dry areas will get drier," says Mahlman.

· The higher latitudes of the Northern Hemisphere will heat up more, relatively speaking, than the rest of the globe, and northern sea ice will be sharply reduced. (Because of its greater mass, Antarctic ice appears more resistant to global warming.)

As a "best guess," says Mahlman, we can expect a 5-degree F warming and a two-foot increase in sea level by the end of the next century -- enough of a rise to imperil many low-lying Pacific islands and other coastal regions. (One country taking this prediction to heart is the Netherlands, which has launched a multibillion-dollar effort to increase the height of its sea walls.)

The GFDL models also suggest we'll see increasingly violent tropical storms and longer, hotter heat waves. And because the extra water vapor will produce more rainfall, surface seawater in higher latitudes will become less salty and thus less likely to sink -- inhibiting the top-to-bottom ocean circulation that's responsible for the Gulf Stream and other important sea currents. Any major change in this ocean turnover could cause shifts in global weather patterns and might also seriously disrupt marine life.

In short, our great-grandchildren can almost certainly look forward to a hotter, more humid, less hospitable planet. And the news gets worse: unless the world makes a titanic effort to reduce fossil-fuel consumption, carbon dioxide levels won't merely double. Once China, Russia, and India develop their industrial bases and start burning their vast coal reserves in earnest, we could well see a quadrupling of atmospheric CO2 by the mid-22nd century. GFDL models predict this would boost the surface temperature by 15 to 20 degrees F in most of North America, Europe, and Asia -- triggering a sea level rise measured in meters rather than feet and causing ocean circulation to virtually disappear.

"If that happens," Mahlman says dryly, "the result will not be fun. In fact, it will be very unfun."

THE POLITICS OF GLOBAL WARMING

Within the United Nations, the greenhouse effect has been officially acknowledged since 1995, when the U.N.'s International Panel on Climate Change noted a "discernible human influence" on world temperatures. The 1997 Kyoto Conference on global warming -- the third of its kind -- was an indication both of how seriously the problem is being taken and how hard it will be to reach a political solution. In the final Kyoto agreement, the major industrial nations, including the U.S., pledged to reduce their CO2 emissions to slightly below 1990 levels by the year 2008 -- a goal that will require major changes in our energy-supply system. Meanwhile, the developing countries (which are expected to be the major source of new CO2 emissions over the next century) were exempted from the deal, over the strenuous objections of the American delegation. As a result, the U.S. Senate is likely to reject the treaty.

"Unfortunately, there are no small fixes," says Mahlman. "Even if Kyoto were ratified, it would only slow the rate of CO2 increase. If we really want to stabilize emissions and hold carbon dioxide levels at double the preindustrial amount, the world is eventually going to have to reduce its fossil-fuel consumption by roughly 70 percent, compared to today's usage. This is going to be very hard, and the social resistance could be massive."

Are electric cars the answer? If you retooled every gas-guzzling auto and truck in the U.S., observes Mahlman, you'd only cut global CO2 emissions by 8 percent -- and that's assuming the electricity came from a non-carbon source. As things stand now, about half the world's electric plants are still powered by coal, while a growing number of other plants run on natural gas.

"Coal is the real problem," Mahlman says. When burned, coal gives off twice as much carbon dioxide as natural gas. It's also cheap, plentiful, and easy to transport, making it a poor country's quickest ticket to affordable electric power plants and a higher standard of living.

Understandably, the developing nations of the world don't want to lose their option of burning coal. The political controversy is heightened by the fact that global warming remains an uncertain science. Over the past 10 years, GFDL has improved its computing power 30-fold and gotten much better at modeling the vagaries of ocean circulation, atmospheric chemistry, and other key variables (its Modular Ocean Model is used by hundreds of researchers worldwide). But all these systems contain perplexing feedback loops that make completely accurate predictions impossible. That's why the experts offer a range of potential outcomes, which can easily be manipulated by different interest groups.

"Environmental groups tend to exaggerate the conclusions of our models to support their own value system." says Mahlman. "They focus on the worst-case projections, and play up recent floods and storms as a symptom of global warming when there's no scientific evidence for this. At the same time, the political right wing does the opposite: they want the issue of global warming to go away, because they don't want their energy supply and lifestyle messed up by icky environmental problems -- and this problem is the grandaddy of them all. They seem to think that the best way to make the issue go away is to dispute or downplay the science."

To illustrate his point, Mahlman quotes from a recent Associated Press story on how the Republican Congress, displeased with the Kyoto treaty, has slashed $200 million from President Clinton's budget for energy conservation and research -- and is now considering a law that would ban the White House and the Environmental Protection Agency from even talking about the subject of global warming. The story notes that in a recent Congressional hearing, the president of the American Coal Company characterized global warming as a "hoax."

A MULTIDISCIPLINARY APPROACH

If the Great Carbon Dioxide Experiment is a hoax, then a lot of scientists have been bamboozled. Amid growing evidence of a temperature rise, the 1990s have seen an explosion of interest in global-warming research. Not too many years ago, GFDL was one of just two or three climate-modeling centers in the world. Today, more than two dozen such centers around the planet are working on various aspects of the greenhouse problem.

GFDL has also helped spawn a new cottage industry at Princeton. Until fairly recently, the only biogeochemist on the faculty was Jorge Sarmiento, a professor in the Department of Geosciences' Atmospheric and Oceanic Sciences Program and an expert on the ocean's carbon cycle. "When I first came here in 1978, the only people I could interact with professionally were at GFDL," Sarmiento recalls. "Then, about six years ago, there was an incredible sea change."

This latest phase began in 1992, when the Department of Ecology and Evolutionary Biology (EEB) hired two new professors. One was Steve Pacala, a biologist who specializes in the terrestrial (land-based) carbon cycle -- a perfect match to Sarmiento's ocean-based expertise. The other was Simon Levin, an expert on the mathematical modeling of ecosystems.

A synergy developed: using a "coupled" atmosphere-ocean model developed by Syukuro Manabe and Ronald Stouffer at GFDL, Sarmiento and Pacala began working on a mathematical model that would track the complete cycle of carbon as it passed through its various incarnations as mineral deposit, atmospheric gas, plant or animal nutrient, and ions in the sea. Meanwhile, Levin became the first director of the Princeton Environmental Institute (PEI), a new interdisciplinary program formed to address major environmental issues by drawing on the pooled expertise of various university departments.

The geosciences department has also hired a host of new talent, including biogeochemist François Morel, who recently took over the directorship of PEI; Michael Bender, an expert on ocean-atmosphere interactions and the earth's climate history; Bess Ward, a biological oceanographer who studies the global nitrogen cycle; and Geoffrey Vallis, whose focus includes climate dynamics and the circulation of the atmosphere and the ocean. PEI has also instituted a postdoctoral fellowship program in environmental science and is seeking funding from the National Science Foundation for a new center that will study the role of trace metals in the environment.

"Princeton is now in a position to be a dominant player in the issue of global warming," says Sarmiento. The interdepartmental nature of PEI and the broad scope of the greenhouse problem itself has led to an unprecedented sharing of information and ideas among different academic groups -- ranging from joint research projects by the geosciences and EEB departments to seminars that bring scientists and economists together with policy experts from the Woodrow Wilson School and energy strategists from the Center for Energy and Environmental Studies. Last February, for example, the university's Center for Economic Policy Studies sponsored a wide-ranging forum on global warming, chaired by economist Alan Blinder '67.

One especially fruitful collaboration has been the partnership of Sarmiento and Pacala -- the oceanographer and the plant biologist. Among other findings, Sarmiento's analysis of the global carbon cycle has produced startling new evidence of how increased rainfall from global warming might change the ocean. Their computer models show that a "lid" of fresh water on the ocean's surface would cause its upper depths to stratify like a layer cake. Says Sarmiento, "This stratification could cause some dramatic shifts in the patterns of marine life -- including fish, phytoplankton, and coral reefs." With less ocean turnover, nutrients wouldn't be distributed to lower depths as well. In the middle latitudes, increased stratification would tend to favor smaller phytoplankton, associated with lower levels of ocean productivity. "It would essentially turn ocean 'forests' into 'deserts,'" says Sarmiento.

In addition, the decrease in ocean turnover caused by higher carbon-dioxide levels is likely to reduce the ability of the sea to absorb CO2. A great deal of Sarmiento and Pacala's research focuses on carbon dioxide "sinks": certain areas of the land and sea that act as carbon drains -- sucking carbon dioxide out of the surrounding atmosphere as fast as it builds up. These carbon sinks now absorb about half of the eight billion tons of CO2 released by humans each year.

The absorption effect appears to be divided roughly equally between ocean and forests. In a recent study based on atmospheric samples, Pacala and Sarmiento have concluded that the North American continent is acting as a major land sink -- draining CO2 out of the air about as quickly as U.S. industry produces it. Pacala believes that trees have something to do with this. "Plants eat CO2 for a living," he explains. "The world's forests exchange a total of 100 billion metric tons of carbon dioxide with the atmosphere each year."

Although the exact locations and mechanisms of these CO2 drains are unknown, the North American sink is probably the result of a historical coincidence. "The U.S. did most of its tree-cutting in the last century," says Pacala. "We're now in a period of reforestation, meaning that more carbon dioxide is being taken up by growing trees, which then store the carbon in their trunks."

According to Pacala, this new finding suggests that regrowing forests in regions of temperate Asia -- which has been largely stripped of trees -- and reversing the rapid deforestation of tropical forests (especially the Amazon Basin) could significantly slow the rise in CO2 levels. But more trees, he warns, would provide at best a temporary fix: "Once we regrow all the world's forests and all that extra carbon has been stored away -- which could take about 50 years -- then we'll have to look for some other solution. Basically, reforestation will buy us a generation's worth of time -- enough extra time, hopefully, to get our act together and start to deal with the fossil-fuel problem."

Three years ago, Sarmiento and Pacala formed the Carbon Modeling Consortium, a research group that also includes scientists from GFDL, Columbia University, NOAA's Climate Monitoring and Diagnostics Laboratory, the Atlantic Ocean Marine Laboratory, and the Pacific Marine Experimental Lab. Funded by a NOAA grant, the consortium will look more closely at how CO2 sinks operate on a local level. To get the necessary raw data, its scientists are banking on a proposed project called Carbon America, which would deploy aircraft to criss-cross the continent, gathering detailed regional information on carbon dioxide concentrations. A similar effort involving ships and buoys will collect information on ocean chemistry.

A national research panel headed by Sarmiento is now studying the possibility of creating a long-term observation network to identify carbon sinks and their sources. "If we can figure out exactly what's causing these CO2 sinks to occur," says Pacala, "we may be able to replicate these conditions in other places."

As the biogeochemists scramble to understand the big picture, Dan Kammen, director of the Woodrow Wilson School's Program in Science, Technology and Environmental Policy, is trying to devise ways to turn this scientific knowledge into useful action. "The discovery about carbon sinks is very important," he says, "because it suggests that we should be encouraging countries to do more than just cut back on carbon dioxide production. Active reforestation can be another part of the solution."

CARBON "BARTERING"

Kammen believes that one way to resolve the us-versus-them debate on carbon emissions could be an international "carbon bartering" system, in which developing nations are charged for the right to burn fossil fuels and given credit for such anti-CO2 measures as replanting forests, promoting energy efficiency, and investing in low-carbon technologies.

"Coal is the big worry," he says. "Right now, 40 to 50 percent of the world's electricity is produced by coal-powered plants. One immediate thing we can do is encourage nations to convert their power plants to natural gas, which contains only half as much carbon as coal. But we still need to get carbon emissions much lower in the long run."

In Kammen's view, the ultimate answer lies with solar power, wind power, biomass energy, and -- if properly managed -- hydroelectric and nuclear energy. "A number of these technologies are poised to become big players in a low-carbon economy," he says, "but we need to invest our financial and human resources in them on a much higher level than we have. It can take decades to develop any new energy technology. If we don't get these technologies started up now, we won't have the flexibility and the options we'll need later, should disaster strike."

In many ways, says Kammen, the developing world is ahead of the game, particularly in the use of solar and wind power and small-scale "micro-hydro" technology, all of which are becoming more cost-effective. "Kenya has more photoelectric devices per capita than anywhere else in the world," he notes. "They're buying 20,000 to 30,000 systems a year. In some villages, the only source of electricity is solar power. It's reliable, and much cheaper than extending the Kenyan electric-power grid at a cost of $10,000 per kilometer."

An even more exotic technological solution can be found floating along the corridors of the Engineering Quadrangle. That's where Rob Socolow, a professor of mechanical and aerospace engineering who recently stepped down as director of the Center for Energy and Environmental Studies, is working with colleagues Robert Williams and Joan Ogden on a novel idea known as "carbon sequestration." In its simplest form, this involves steam-treating natural gas or coal to transform its carbon content into carbon dioxide, leaving pure hydrogen behind. This hydrogen can then be used in hydrogen fuel cells to provide electric power and transportation (the cells are already being tested in prototype cars and buses). The unwanted carbon dioxide would be pumped into underground aquifers, deep coal seams, or the deep ocean, where it would remain indefinitely.

"I like this idea is because it's doable," says Socolow. "Hydrogen fuel cells exist and are getting better all the time. We also have experience with hydrogen production from fossil fuels, and with carbon dioxide transport. There's a well-developed oil recovery industry that sends CO2 over miles of pipeline and then pumps it deep into oil fields."

It's already clear that the idea works: motivated by Norway's national tax on CO2 emissions, Statoil, that country's leading oil and gas company, has been employing a form of carbon sequestration in its offshore natural gas operations for the past three years -- separating CO2 from the combustible component of gas and storing it safely away inside a nearby aquifer.

Each of these solutions is only part of the answer, however. They're all feasible, but the question remains: can they possibly provide enough low-carbon energy to run a world where the population is likely to grow by 50 percent over the next century?

ENERGY FROM NUCLEAR FUSION

"To bring all the world's nations up to a reasonable standard of living by 2050, we'll need about three times more energy than we're using now," says Rob Goldston *77, director of the Princeton Plasma Physics Laboratory (PPPL). "But the models tell us that if we want to level off carbon dioxide levels, we'll have to produce three times less CO2. In other words, we have to become 10 times more efficient in our use of carbon -- that's a different world than the one we're living in."

Goldston's office is also located on Forrestal Campus, just a short stroll down a tree-lined road from the climate-modelers at GFDL. Since the 1960s, scientists at PPPL have been quietly pursuing the Holy Grail of low-carbon power: fusion energy. Unlike nuclear fission, which splits atoms, fusion energy is created by getting hydrogen atoms to bond together, forming helium plus lots and lots of energy. The primary fuel for this reaction is deuterium, a hydrogen isotope found in sea water.

Fusion energy is also what powers the sun and hydrogen bombs. If fusion can be controlled and harnessed in a controlled way, it could provide another important source of low-cost, CO2-free energy in the future. For now, however, that's still a big "if." To create a fusion reaction, researchers must first heat the hydrogen isotopes to well over one million degrees inside a huge accelerator, while pinning this superheated plasma into place with a powerful magnetic field. So far, fusion experiments have produced only brief pulses of energy -- but those pulses are gradually expanding, according to Goldston.

"In 1973, in my second year as a Princeton graduate student, we had our first breakthrough -- producing 1/100th of a watt for 1/200th of second," he recalls. "Now, we're making over 10 million watts for the better part of a second. We've made very good progress, but the next steps will be more expensive." Scientists are working toward two goals: a bigger pulse (something like one billion watts will be needed to make a power plant viable) and a longer pulse. "These problems can be overcome," adds Goldston, "but only if the world's governments come up with the funds."

He speaks from experience: a few years ago, Congress abruptly ended funding for Princeton's largest fusion device, called a Tokamak. PPPL has continued its work on basic fusion research using a similar device at MIT and another in San Diego. In the meantime, Goldston and his colleagues are looking forward to next April, when the Forrestal facility will christen a new, more compact type of accelerator known as a Spherical Torus. The lab also has a proposal pending to build a Stellarator -- an even more advanced machine, which has its roots in the research of Princeton's fusion pioneer, the late Lyman Spitzer *38.

"If all goes well, we're talking about having working fusion energy on line by the middle of the next century," Goldston says. "I'm very optimistic that the science will be there -- but it's going to take an international collaboration. Unfortunately, while it's easy for people to plan for their grandchildren, it's hard for governments to think that far ahead. The real issue is whether the governments of the world have the political will to deal with something that won't be commercially available until 50 years from now."

Royce Flippin '80 is a freelance writer who lives in East Brunswick, New Jersey. For more information on global warming, visit GFDL's Website, at www.gfdl.gov.