When global warming first emerged as a potential crisis in the late '80s, one academic analyst called it "the public policy problem from hell." The years since have only proven him more astute--15 years into our understanding of climate change, we have yet to figure out how we're going to tackle it. And environmentalists are just as clueless as anyone else: Do we need to work on lifestyles or on lobbying, on politics or on photovoltaics? And is there a difference? How well we handle global warming will determine what kind of century we inhabit-- and indeed what kind of planet we leave behind to everyone and everything that follows us down into geologic time. It is the environmental question, the one that cuts closest to home and also floats off most easily into the abstract. So far it has been the ultimate "can't get there from here" problem, but the time has come to draw a roadmap--one that may help us deal with the handful of other issues on the list of real, world-shattering problems.

The first thing to know about global warming is this: The science is sound. In 1988, when scientists first testified before Congress about the potential for rapid and destabilizing climate change, they were still describing a hypothesis. It went like this: Every time human beings burn coal, gas, oil, wood or any other carbon-based fuel, they emit large quantities of carbon dioxide. (A car emits its own weight in carbon annually if you drive it the average American distance.) This carbon dioxide accumulates in the atmosphere. It's not a normal pollutant--it doesn't poison you, or change the color of the sunset. But it does have one interesting property: Its molecular structure traps heat near the surface of the planet that would otherwise radiate back out to space. It acts like the panes of glass on a greenhouse.

The hypothesis was that we were putting enough carbon dioxide into the atmosphere

Glaciers like this one in Greenland are retreating at an unprecedented rate. KRT PHOTO

to make a difference. The doubters said no--that the earth would compensate for any extra carbon by forming extra clouds and cooling the planet, or through some other feedback mechanism. And so, as scientists will, they went at it. For five years--lavishly funded by governments that wanted to fund research instead of making politically unpopular changes--scientists produced paper after paper. They studied glacial cores and tree rings and old pollen sediments in lake beds to understand past climates; they took temperature measurements on the surface and from space; they refined their computer models and ran them backward in time to see if they worked. By 1995 they had reached a conclusion. That year the Intergovernmental Panel on Climate Change (IPCC), a group of all the world's climatologists assembled under the auspices of the United Nations, announced that human beings were indeed heating up the planet.

The scientists kept up the pace of their research for the next five years, and in the past five months have published a series of massive updates to their findings. These results are uniformly grimmer than even five years before. They include:

• The prediction that humans will likely heat the planet 4 to 6 degrees Fahrenheit in this century, twice as much as earlier forecast, taking global temperatures to a level not seen in millions of years, and never before in human history.

• The worst-case possibility that we will raise the temperature by as much as 11 degrees Fahrenheit, a true science-fiction scenario that no one had seriously envisaged before.

• The near certainty that these temperature increases will lead to rises in sea level of at least a couple of feet

• The well-documented fear that disease will spread quickly as vectors like mosquitoes expand their range to places that used to be too cool for their survival.

But it isn't just the scientists who are hard at work on this issue. For the past five years, it's almost as if the planet itself has been peer-reviewing their work. We've had the warmest years on record--including 1998, which was warmer than any year for which records exist. And those hot years have shown what even small changes in temperature--barely a degree Fahrenheit averaged globally--can do to the earth's systems.

Consider hydrology, for instance. Warm air holds more water vapor than cold air, so there is an increase in evaporation in dry areas, and hence more drought--something that has been documented on every continent. Once that water is in the atmosphere, it's going to come down somewhere--and indeed we have seen the most dramatic flooding ever recorded in recent years. In 1998, 300 million humans, one in 20 of us, had to leave their homes for a week, a month, a year, forever because of rising waters.

Or look at the planet's cryosphere, its frozen places. Every alpine glacier is in retreat; the snows of Kilimanjaro will have vanished by 2015; and the Arctic ice cap is thinning fast--data collected by U.S. and Soviet nuclear submarines show that it is almost half gone compared with just four decades ago.

In other words, human beings are changing the planet more fundamentally in the course of a couple of decades than in all the time since we climbed down from the trees and began making clever use of our opposable thumbs. There's never been anything like this.

Yet to judge from the political response, this issue ranks well below, say, the estate tax as a cause for alarm and worry. In 1988, there was enough public outcry that George Bush the Elder promised to combat "the greenhouse effect with the White House effect." In 1992, Bill Clinton promised that Americans would emit no more carbon dioxide by 2000 than they had in 1990--and that his administration would do the work of starting to turn around our ocean liner of an economy, laying the foundation for the transition to a world of renewable energy.

That didn't happen, of course. Fixated on the economy, Clinton and Gore presided over a decade when Americans, who already emitted a quarter of the world's carbon dioxide, actually managed to increase their total output by 12 percent. Now we have a president who seems unsure whether global warming is real, and far more concerned with increasing power production than with worrying about trifles like the collapse of the globe's terrestrial systems. In November, the hope of global controls on carbon dioxide production essentially collapsed at an international conference in the Hague, when the United States refused to make even modest concessions on its use of fossil fuels, and the rest of the world finally walked away from the table in disgust.

In the face of all this, what is an environmentalist to do? The normal answer, when you're mounting a campaign, is to look for self-interest, to scare people by saying what will happen to us if we don't do something: all the birds will die, the canyon will disappear beneath a reservoir, we will choke to death on smog.

But in the case of global warming, those kind of answers don't exactly do the trick, at least in the timeframe we're discussing. At this latitude, climate change will creep up on us. Severe storms have already grown more frequent and more damaging. The seasons are less steady in their progression. Some agriculture is less reliable. But face it: Our economy is so enormous that it handles those kinds of changes in stride. Economists who work on this stuff talk about how it will shave a percentage or two off GNP over the next few decades--not enough to notice in the kind of generalized economic boom they describe. And most of us live lives so divorced from the natural world that we hardly notice the changes anyway. Hotter? Turn up the air conditioning. Stormier? Well, an enormous percentage of Americans commute from remote-controlled garage to office parking garage--they may have gone the last year without getting good and wet in a rainstorm. By the time the magnitude of the change is truly in our faces, it will be too late to do much about it: There's such a lag time with carbon dioxide in the atmosphere that we need to be making the switch to solar and wind and hydrogen right about now. Yesterday, in fact.

So maybe we should think of global warming in a different wayÐÐas the great moral crisis of our moment, the equivalent in our time of the civil rights movement of the '60s.

Why a moral question? In the first place, because we've never figured out a more effective way to screw the marginalized and poor of this planet. Having taken their dignity, their resources and their freedom under a variety of other schemes, we now are taking the very physical stability on which they depend for the most bottom-line of existences.

Our economy can absorb these changes for a while, but for a moment consider Bangladesh. A river delta that houses 130 million souls in an area the size of Wisconsin, Bangladesh actually manages food self-sufficiency most years. But in 1998, the sea level in the Bay of Bengal was higher than normal, just the sort of thing we can expect to become more frequent and severe. The waters sweeping down the Ganges and the Brahmaputra from the Himalayas could not drain easily into the ocean--they backed up across the country, forcing most of its inhabitants to spend three months in thigh-deep water. The fall rice crop didn't get planted. We've seen this same kind of disaster in the last few years in Mozambique or Honduras or Venezuela or any of a dozen other wretched spots.

And a moral crisis, too, if you place any value on the rest of creation. Coral reef researchers indicate that these spectacularly intricate ecosystems are also spectacularly vulnerable--rising water temperatures will likely bleach them to extinction by mid-century. In the Arctic, polar bears are 20 percent scrawnier than they were a decade ago: As pack ice melts, so does the opportunity for hunting seals. All in all, this century seems poised to see extinctions at a rate not observed since the last big asteroid slammed into the planet. But this time the asteroid is us.

A moral question, finally, if you think we owe any debt to the future. No one ever has figured out a more thorough-going way to stripmine the present and degrade what comes after. Forget the seventh generation--we're talking 70th generation, and 700th. All the people that will ever be related to you. Ever. No generation yet to come will ever forget us--we are the ones present at the moment when the temperature starts to spike, and so far we have not reacted. If it had been done to us, we would loathe the generation that did it, precisely as we will one day be loathed.

But trying to make a moral campaign is no easy task. In most moral crises, there is a villain--some person or class or institution that must be overcome. Once they're identified, the battle can commence. But you can't really get angry at carbon dioxide, and the people responsible for its production are, well, us. So perhaps we need some symbols to get us started, some places to sharpen the debate and rally ourselves to action. There are plenty to choose from: our taste for ever bigger houses and the heating and cooling bills that come with them; our penchant for jumping on airplanes at the drop of a hat; and so on. But if you wanted one glaring example of our lack of balance, you could do worse than point the finger at sport utility vehicles.

SUVs are more than mere symbol. They are a major part of the problem--one reason we emit so much more carbon dioxide now than we did a decade ago is because our fleet of cars and trucks actually has gotten steadily less fuel efficient for the past 10 years. If you switched today from the average American car to a big SUV, and drove it for just one year, the difference in carbon dioxide that you produced would be the equivalent of opening your refrigerator door and then forgetting to close it for six years. SUVs essentially are machines for burning fossil fuel that just happen to also move you and your stuff around.

But what makes them such a perfect symbol is the brute fact that they are simply unnecessary. Go to the parking lot of the nearest suburban supermarket and look around: the only conclusion you can draw is that to reach the grocery, people must drive through three or four raging rivers and up the side of a trackless canyon. These are semi-military machines (some, like the Hummer, are not semi at all), Brinks trucks on a slight diet. They don't keep their occupants safer, they do wreck whatever they plow into--they are the perfect metaphor for a heedless, supersized society. And a gullible one, which has been sold on these vast vehicles partly by the promise that they somehow allow us to commune with nature.

That's why we need a much broader politics than the White House-lobbying that's occupied the big enviros for the past decade, or the mass-market mailing that has been their stock in trade for the past quarter century. We need to take all the brilliant and energetic strategies of local grassroots groups fighting dumps and cleaning up rivers, and we need to make those tactics national and international. So that's why some pastors are starting to talk with their congregations about what car they're going to buy, and why some college seniors are passing around petitions pledging to stay away from the Ford Explorers and Excursions and Extraneouses, and why some few auto dealers have begun to notice informational picketers outside on Saturday mornings urging their customers to think about gas mileage when they go inside.

The point is not that by themselves such actions--any individual actions--will make any real dent in the production of carbon dioxide pouring into our atmosphere. Even if you got 10 percent of Americans really committed to changing energy use, their solar homes wouldn't make much of a dent in our national totals. But 10 percent would be enough to change the politics of the issue, to insure the passage of the laws that would cause us all to shift our habits. And so we need to begin to take an issue that is now the province of technicians and turn it into a political issue--just as bus boycotts began to take the issue of race and make it public, forcing the system to respond. That response is likely to be ugly--there are huge companies with a lot to lose, and many people so tied in to their current ways of life that advocating change smacks of subversion. But this has to become a political issue--and fast. The only way that may happen, short of a hideous drought or monster flood, is if it becomes a personal issue first.

Bill McKibben is an environmentalist and former staff writer for The New Yorker whose work has appeared in Outside, Rolling Stone, Harper's and many other publications. He is the author of The End of Nature and Long Distance.

Now read "10 Facts About SUVs."