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It was probably always too much to believe that human beings would be responsible stewards of the planet. We may be the smartest of all the animals, endowed with exponentially greater powers of insight and abstraction, but we're animals all the same. That means that we can also be shortsighted and brutish, hungry for food, resources, land--and heedless of the mess we leave behind trying to get them.

And make a mess we have. If droughts and wildfires, floods and crop failures, collapsing climate-sensitive species and the images of drowning polar bears didn't quiet most of the remaining global-warming doubters, the hurricane-driven destruction of New Orleans did. Dismissing a scientist's temperature chart is one thing. Dismissing the death of a major American city is something else entirely. What's more, the heat is only continuing to rise. This past year was the hottest on record in the U.S. The deceptively normal average temperature this winter masked record-breaking highs in December and record-breaking lows in February. That's the sign not of a planet keeping an even strain but of one thrashing through the alternating chills and night sweats of a serious illness.

The U.N.'s Intergovernmental Panel on Climate Change issued a report on the state of planetary warming in February that was surprising only in its utter lack of hedging. "Warming of the climate system is unequivocal," the report stated. What's more, there is "very high confidence" that human activities since 1750 have played a significant role by overloading the atmosphere with carbon dioxide hence retaining solar heat that would otherwise radiate away. The report concludes that while the long-term solution is to reduce the levels of CO2 in the atmosphere, for now we're going to have to dig in and prepare, building better levees, moving to higher ground, abandoning vulnerable floodplains altogether. When former Vice President Al Gore made his triumphant return to Capitol Hill on March 21 to testify before Congress on climate change, he issued an uncompromising warning: "We do not have time to play around with this."

Some lingering critics still found wiggle room in the U.N. panel's findings. "I think there is a healthy debate ongoing, even though the scientists who are in favor of doing something on greenhouse gases are in the majority," says Republican Congressman James Sensenbrenner of Wisconsin. But when your last good position is to debate the difference between certain and extra certain, you're playing a losing hand. "The science," says Christine Todd Whitman, former administrator of the Environmental Protection Agency (epa), "now is getting to the point where it's pretty hard to deny." Indeed it is. Atmospheric levels of CO2 were 379 parts per million (p.p.m.) in 2005, higher than at any time in the past 650,000 years. Of the 12 warmest years on record, 11 occurred between 1995 and 2006.

So if the diagnosis is in, what's the cure? A crisis of this magnitude clearly calls for action that is both bottom-up and top-down. Though there is some debate about how much difference individuals can make, there is little question that the most powerful players--government and industry--have to take the lead.

Still, individuals too can move the carbon needle, but how much and how fast? Different green strategies, after all, yield different results. (See "51 Things We Can Do," page 69.) You can choose a hybrid vehicle, but simply tuning up your car and properly inflating the tires will help too. Buying carbon offsets can reduce the impact of your cross-continental travel, provided you can ensure where your money's really going. Planting trees is great, but in some parts of the world, the light-absorbing color of the leaves causes them to retain heat and paradoxically increases warming.

Even the most effective individual action, however, is not enough. Cleaning up the wreckage left by our 250-year industrial bacchanal will require fundamental changes in a society hooked on its fossil fuels. Beneath the grass-roots action, larger tectonic plates are shifting. Science is attacking the problem more aggressively than ever. So is industry. So are architects and lawmakers and urban planners. The world is awakened to the problem in a way it never has been before. Says Carol Browner, onetime administrator of the EPA: "It's a sea change from where we were on this issue." Here are the ways that sea is shifting the most:

The Scientists' Solutions

If the Earth is choking on greenhouse gases, it's not hard to see why. Global carbon dioxide output last year approached a staggering 32 billion tons, with about 25% of that coming from the U.S. Turning off the carbon spigot is the first step, and many of the solutions are familiar: windmills, solar panels, nuclear plants. All three technologies are part of the energy mix, although each has its issues, including noise from windmills and radioactive waste from nukes.

Biofuels, however, are the real growth science, particularly after President George W. Bush, in his State of the Union address, called for the U.S. to quintuple its production of biofuels, primarily ethanol. That was good news to American corn farmers, who produce the crop from which the overwhelming share of domestic ethanol is made. But the manufacture of corn ethanol is still inefficient: the process burns up almost as much energy as it produces.

A better answer is sugarcane ethanol, which yields eight times the energy it takes to make and provides 40% of all the fuel sold in Brazil. But such ethanol causes environmental problems of its own, as forests are cleared for cane fields. Better still would be to process ethanol from agricultural waste like wood chips or the humble summer grass called switchgrass. The cellulosic ethanol they produce packs more energy than corn ethanol, but it also takes more energy to manufacture. "If you make ethanol by burning coal, you defeat the purpose," says Sarah Hessenflow Harper, an analyst for the advocacy group Environmental Defense.

Until we can dial down the carbon, a more immediate strategy might be to find somewhere to put it all--to sequester it underground. In the same way we store radioactive waste from nuclear reactors, so too could we collect the gaseous CO2 from power plants.