Crutzen's embrace of geoengineering was considered such a heresy within the climate-science community that some peers tried to stop publication of his essay. How could the man reverently known as "Dr. Ozone" possibly endorse such a scheme? Wouldn't the environmental damage outweigh the benefits?

Actually, no. Crutzen concluded that damage to the ozone would be minimal. The sulfur dioxide would eventually settle out in the polar regions but in such relatively small amounts that there, too, significant harm was unlikely. If a problem did arise, Crutzen wrote, the sulfur injection "could be stopped on short notice...which would allow the atmosphere to return to its prior state within a few years."

Another fundamental objection to geoengineering is that it intentionally alters the earth's natural state. To that, Myhrvold has a simple answer: "We've already geoengineered the earth."

In just a few centuries, we will have burned up most of the fossil fuel that took 300 million years of biological acc.u.mulation to make. Compared with that, injecting a bit of sulfur into the sky seems pretty mild. As Lowell Wood points out, sulfur isn't even the optimal chemical for a stratospheric shield. Other, less noxious-sounding materials-aluminized plastic micro beads, for instance-could make an even more efficient sunscreen. But sulfur is the most palatable choice "simply because we've got the volcano proof of feasibility," Wood says, "and along with that, a proof of harmlessness."

Wood and Myhrvold do worry that Budyko's Blanket might create an "excuse to pollute." That is, rather than buying time for us to create new energy solutions, it would lure people into complacency. But blaming geoengineering for this, Myhrvold says, is like blaming a heart surgeon for saving the life of someone who fails to exercise and eats too many french fries.

Perhaps the single best objection to the garden hose idea is that it is too simple and too cheap. As of this writing, there is no regulatory framework to prohibit anyone-a government, a private inst.i.tution, even an individual-from putting sulfur dioxide in the atmosphere. (If there were, many of the world's nearly eight thousand coal-burning electricity units would be in a lot of trouble.) Still, Myhrvold admits that "it would freak people out" if someone unilaterally built the thing. But of course this depends on the individual. If it were Al Gore, he might snag a second n.o.bel Peace Prize. If it were Hugo Chavez, he'd probably get a prompt visit from some U.S. fighter jets.

One can also imagine the wars that might break out over who controls the dials on Budyko's Blanket. A government that depends on high oil prices might like to crank up the sulfur to keep things extra cool; others, meanwhile, might be happier with longer growing seasons.

Lowell Wood recounts a lecture he once gave, during which he mentioned that a stratospheric shield could also filter out damaging ultraviolet rays. An audience member suggested that fewer ultraviolet rays would lead to more people getting rickets.

"My response," Wood says, "was that your pharmacist can take care of that with vitamin D, and it'll be better for your overall health as well."

All the rocket scientists, climate scientists, physicists, and engineers around the IV conference table chuckle at Wood's riposte. Then someone asks if IV, with Budyko's Blanket up its sleeve, should be working toward a rickets-prevention patent. Now they laugh louder.

But it's not entirely a joke. Unlike most of the patents IV owns, Budyko's Blanket has no clear route to profits. "If you were an investor of mine," Myhrvold says, "you might ask: 'Remind me again why you're working on this?'" Indeed, many of IV's most time-consuming projects, including a variety of AIDS and malaria solutions, are substantially pro bono work.

"This is the world's greatest philanthropist sitting on the other side of the table," Wood says with a chuckle and a nod toward Myhrvold. "Involuntarily so, but there he is."

As dismissive as Myhrvold can be toward the prevailing sentiments on global warming, he is quick to deny that he dismisses global warming itself. (If that were the case, he'd hardly spend so much of his company's resources working on solutions.) Nor is he arguing for an immediate deployment of Budyko's Blanket-but, rather, that technologies like it be researched and tested so they are ready to use if the worst climate predictions were to come true.

"It's a bit like having fire sprinklers in a building," he says. "On the one hand, you should make every effort not to have a fire. But you also need something to fall back on in case the fire occurs anyway." Just as important, he says, "it gives you breathing room to move to carbon-free energy sources."

He is also eager to get geoengineering moving forward because of what he sees as "a real head of steam" that global-warming activists have gathered in recent years.

"They are seriously proposing doing a set of things that could have enormous impact-and we think probably negative impact-on human life," he says. "They want to divert a huge amount of economic value toward immediate and precipitous anti-carbon initiatives, without thinking things through. This will have a huge drag on the world economy. There are billions of poor people who will be greatly delayed, if not entirely precluded, from attaining a First World standard of living. In this country, we can pretty much afford the luxury of doing whatever we want on the energy-and-environment front, but other parts of the world would seriously suffer."

Certain new ideas, no matter how useful, are invariably seen as repugnant. As we mentioned earlier, a market for human organs-even though it might save tens of thousands of lives each year-is one such example.

Over time, some ideas do cross the repugnance barrier to become reality. Charging interest on loans. Selling human sperm and eggs. Profiting from a loved one's premature death. This last example of course describes how life insurance works. Today it is standard practice to wager on your own death in order to provide for your family. Until the mid-nineteenth century, life insurance was considered "a profanation," as the sociologist Viviana Zelizer writes, "which transformed the sacred event of death into a vulgar commodity."

Budyko's Blanket may simply be too repugnant a scheme to ever be given a chance. Intentional pollution? Futzing with the stratosphere? Putting the planet's weather in the hands of a few arrogant souls from Seattle? It is one thing for climate heavyweights like Paul Crutzen and Ken Caldeira to endorse such a solution. But they are mere scientists. The real heavyweights in this fight are people like Al Gore.

And what does he think of geoengineering?

"In a word," Gore says, "I think it's nuts."

If the garden-hose-to-the-sky idea doesn't fly, IV has another proposal that relies on the same science but is perhaps slightly less repugnant. As it turns out, the amount of stratospheric sulfur necessary to cool the planet is equal to the amount that just a handful of coal-burning power plants already belch out. This second plan calls for simply extending the smokestacks at a few strategically located plants. So instead of spewing their sulfur-laden smoke several hundred feet into the air, these smokestacks would release it some eighteen miles high, into the stratosphere, where it would have the same net cooling effect as the garden-hose scheme.

This plan is appealing because it simply repurposes existing pollution without adding any more. Although an eighteen-mile-high smokestack might sound like a hard thing to build, IV has figured out how-essentially by attaching a long, skinny hot-air balloon to an existing power-plant smokestack, creating a channel that lets the hot sulfur gases rise by their own buoyancy into the stratosphere. This project is dubbed, naturally, "chimney to the sky."

And if even that plan is too repugnant, IV has something entirely different, a plan that is practically heavenly: a sky full of puffy white clouds.

This is the brainchild of John Latham, a British climate scientist who recently joined the IV stable of inventors. Latham is a gentle, soft-spoken man in his late sixties who is also a rather serious poet. So it caught his ear when, long ago, he stood on a mountaintop in North Wales with his eight-year-old son Mike, gazing down at a sunset, and the boy, pointing out how shiny the clouds were, called them "soggy mirrors."

Precisely!

"On balance, the role of clouds is to produce a cooling," says Latham. "If clouds didn't exist in the atmosphere, the earth would be a lot hotter than it is now."

Even man-made clouds-the contrails from a jet plane, for instance-have a cooling effect. After the September 11 terrorist attacks, all commercial flights in the United States were grounded for three days. Using data from more than four thousand weather stations across the country, scientists found that the sudden absence of contrails accounted for a subsequent rise in ground temperature of nearly 2 degrees Fahrenheit, or 1.1 degrees Celsius.

There are at least three essential ingredients for the formation of clouds: ascending air, water vapor, and solid particles known as cloud condensation nuclei. When planes fly, particles in the exhaust plume serve as the nuclei. Over landma.s.ses, dust particles do the job. But there are far fewer cloud-friendly nuclei over the world's oceans, Latham explains, so the clouds contain fewer droplets and are therefore less reflective. As a result, more sunlight reaches the earth's surface. The ocean, because it is dark, is particularly good at absorbing the sun's heat.

By Latham's calculations, an increase of just 10 or 12 percent of the reflectivity of oceanic clouds would cool the earth enough to counteract even a doubling of current greenhouse gas levels. His solution: use the ocean itself to make more clouds.

As it happens, the salt-rich spray from seawater creates excellent nuclei for cloud formation. All you have to do is get the spray into the air several yards above the ocean's surface. From there, it naturally lofts upward to the alt.i.tude where clouds form.

IV has considered a variety of ways to make this happen. At the moment, the favorite idea is a fleet of wind-powered fibergla.s.s boats, designed by Stephen Salter, with underwater turbines that produce enough thrust to kick up a steady stream of spray. Because there is no engine, there is no pollution. The only ingredients-seawater and air-are of course free. The volume of spray (and, therefore, of cloud reflectivity) would be easily adjustable. Nor would the clouds reach land, where sunshine is so important to agriculture. The estimated price tag: less than $50 million for the first prototypes and then a few billion dollars for a fleet of vessels large enough to offset projected warming at least until 2050. In the annals of cheap and simple solutions to vexing problems, it is hard to think of a more elegant example than John Latham's soggy mirrors-geoengineering that the greenest green could love.

That said, Myhrvold fears that even IV's gentlest proposals will find little favor within certain environmentalist circles. To him, this doesn't compute.

"If you believe that the scary stories could be true, or even possible, then you should also admit that relying only on reducing carbon-dioxide emissions is not a very good answer," he says. In other words: it's illogical to believe in a carbon-induced warming apocalypse and believe that such an apocalypse can be averted simply by curtailing new carbon emissions. "The scary scenarios could occur even if we make herculean efforts to reduce our emissions, in which case the only real answer is geoengineering."

Al Gore, meanwhile, counters with his own logic. "If we don't know enough to stop putting 70 million tons of global-warming pollution into the atmosphere every day," he says, "how in G.o.d's name can we know enough to precisely counteract that?"

But if you think like a cold-blooded economist instead of a warmhearted humanist, Gore's reasoning doesn't track. It's not that we don't know how to stop polluting the atmosphere. We don't want to stop, or aren't willing to pay the price.

Most pollution, remember, is a negative externality of our consumption. As hard as engineering or physics may be, getting human beings to change their behavior is probably harder. At present, the rewards for limiting consumption are weak, as are the penalties for overconsuming. Gore and other environmentalists are pleading for humankind to consume less and therefore pollute less, and that is a n.o.ble invitation. But as incentives go, it's not a very strong one.

And collective behavior change, as beguiling as that may sound, can be maddeningly elusive. Just ask Ignatz Semmelweis.

Back in 1847, when he solved the mystery of puerperal fever, Semmelweis was hailed as a hero-wasn't he?

Quite the opposite. Yes, the death rate in Vienna General's maternity ward plummeted when he ordered doctors to wash their hands after performing autopsies. Elsewhere, however, doctors ignored Semmelweis's findings. They even ridiculed him. Surely, they reasoned, such a ravaging illness could not be prevented simply by washing one's hands! Moreover, doctors of that era-not the humblest lot-couldn't accept the idea that they were the root of the trouble.

Semmelweis grew frustrated, and in time his frustration curdled into vitriol. He cast himself as a scorned messiah, labeling every critic of his theory a murderer of women and babies. His arguments were often nonsensical; his personal behavior became odd, marked by lewdness and s.e.xual impropriety. In retrospect, it's safe to say that Ignatz Semmelweis was going mad. At the age of forty-seven, he was tricked into entering a sanitarium. He tried to escape, was forcibly restrained, and died within two weeks, his reputation shattered.

But that doesn't mean he wasn't right. Semmelweis was posthumously vindicated by Louis Pasteur's research in germ theory, after which it became standard practice for doctors to scrupulously clean their hands before treating patients.

So do contemporary doctors follow Semmelweis's orders?

A raft of recent studies have shown that hospital personnel wash or disinfect their hands in fewer than half the instances they should. And doctors are the worst offenders, more lax than either nurses or aides.

This failure seems puzzling. In the modern world, we tend to believe that dangerous behaviors are best solved by education. That is the thinking behind nearly every public-awareness campaign ever undertaken, from global warming to AIDS prevention to drunk driving. And doctors are the most educated people in the hospital.

In a 1999 report called "To Err Is Human," the Inst.i.tute of Medicine estimated that between 44,000 and 98,000 Americans die each year because of preventable hospital errors-more than deaths from motor-vehicle crashes or breast cancer-and that one of the leading errors is wound infection. The best medicine for stopping infections? Getting doctors to wash their hands more frequently.

In the wake of this report, hospitals all over the country hustled to fix the problem. Even a world-cla.s.s hospital like Cedars-Sinai Medical Center in Los Angeles found it needed improvement, with a hand-hygiene rate of just 65 percent. Its senior administrators formed a committee to identify the reasons for this failure.

For one, they acknowledged, doctors are incredibly busy, and time spent washing hands is time not spent treating patients. Craig Feied, our emergency-room revolutionary from Washington, estimates that he often interacted with more than one hundred patients per shift. "If I ran to wash my hands every time I touched a patient, following the protocol, I'd spend nearly half my time just standing over a sink."