The warm surface layer is lighter than the cold water beneath, and therefore stays on the surface. "So what we need to do is fix that," he says.

It is a tantalizing puzzle-all that cold water, trillions upon trillions of gallons, lying just beneath the warm surface and yet impotent to defuse the potential disaster.

But Nathan has a solution. It is basically "an inner tube with a skirt," he says with a laugh. That is, a large floating ring, anywhere from thirty to three hundred feet across, with a long flexible cylinder affixed to the inside. The ring might be made from old truck tires, filled with foamed concrete and lashed together with steel cable. The cylinder, extending perhaps six hundred feet deep into the ocean, could be fashioned from polyethylene, aka the plastic used in shopping bags.

"That's it!" Nathan crows.

How does it work? Imagine one of these skirted inner tubes-a giant, funky, man-made jellyfish-floating in the ocean. As a warm wave splashes over the top, the water level inside the ring rises until it is higher than the surrounding ocean. "When you have water elevated above the surface in a tube like that," Nathan explains, "it's called 'hydraulic head.'"

Hydraulic head is a force, created by the energy put into the waves by wind. This force would push the warm surface water down into the long plastic cylinder, ultimately flushing it out at the bottom, far beneath the surface. As long as the waves keep coming-and they always do-the hydraulic head's force would keep pushing surface water into the cooler depths, which inevitably lowers the ocean's surface temperature. The process is low-impact, non-polluting, and slow: a molecule of warm surface water would take about three hours to be flushed out the bottom of the plastic cylinder.

Now imagine deploying these floats en ma.s.se in the patches of ocean where hurricanes grow. Nathan envisions "a picket fence" of them between Cuba and the Yucatan and another skein off the southeastern seaboard of the United States. They'd also be valuable in the South China Sea and in the Coral Sea off the coast of Australia. How many would be needed? Depending on their size, a few thousand floats might be able to stop hurricanes in the Caribbean and the Gulf of Mexico.

A simple throwaway version of this contraption could be built for roughly $100 apiece, although the larger costs would come in towing and anchoring the floats. There's also the possibility of more durable and sophisticated versions, remote-controlled units that could be relocated to where they are most needed. A "smart" version could even adjust the rate at which it cools the surface water by varying the volume of warm water it takes in.

The most expensive float Nathan envisions would cost $100,000. Even at that price, allocating 10,000 of them around the world would cost just $1 billion-or one-tenth the amount of hurricane property damage incurred in a single year in the United States alone. As Ignatz Semmelweis learned about hand-washing and as millions of heart patients learned about cheap pills like aspirin and statins, an ounce of prevention can be worth a few tons of cure.

Nathan isn't yet sure the float will work. For months it has been undergoing intense computer modeling; soon it will be tried out in real water. But all indications are that he and his friends have invented a hurricane killer.

Even if it were capable of eliminating tropical storms entirely, that wouldn't be wise, since storms are part of the natural climate cycle and deliver much-needed rainfall to land. The real value comes from cooling down a Category 5 storm into a less destructive one. "You might be able to manipulate the monsoon rain cycle in tropical areas," Nathan enthuses, "and smooth out the boom-or-bust nature of rainfall in the Sahel in Africa, aiming to prevent starvation."

The float might also improve the ocean's ecology. As surface water heats up each summer, it becomes depleted of oxygen and nutrients, creating a dead zone. Flushing the warm water downward would bring rich, oxygenated cold water to the surface, which ought to substantially enhance sea life. (The same effect can be seen today around offsh.o.r.e oil platforms.) The float might also help sink some of the excess carbon dioxide that has been absorbed by the ocean's surface in recent decades.

There remains, of course, the question of how, and by whom, these floats would be deployed. The Department of Homeland Security recently solicited hurricane-mitigation ideas from various scientists, including Nathan and his friends. Although such agencies rarely opt for cheap and simple solutions-it simply isn't in their DNA-perhaps an exception will be made in this case, for the potential upside is large and the harm in trying seems minimal.

As dangerous as hurricanes are, there looms within the realm of nature a far larger problem, one that threatens to end civilization as we know it: global warming. If only Nathan and his friends, such smart and creative thinkers who aren't afraid of simple solutions, could do something about that...

CHAPTER 5

WHAT DO AL GORE AND MOUNT PINATUBO HAVE IN COMMON?

The headlines have been harrowing, to say the least.

"Some experts believe that mankind is on the threshold of a new pattern of adverse global climate for which it is ill-prepared," one New York Times article declared. It quoted climate researchers who argued that "this climatic change poses a threat to the people of the world."

A Newsweek article, citing a National Academy of Sciences report, warned that climate change "would force economic and social adjustments on a worldwide scale." Worse yet, "climatologists are pessimistic that political leaders will take any positive action to compensate for the climatic change or even to allay its effects."

Who in his or her right mind wouldn't be scared of global warming?

But that's not what these scientists were talking about. These articles, published in the mid-1970s, were predicting the effects of global cooling.

Alarm bells had rung because the average ground temperature in the Northern Hemisphere had fallen by .5 degrees Fahrenheit (.28 degrees Celsius) from 1945 to 1968. Furthermore, there had been a large increase in snow cover and, between 1964 and 1972, a decrease of 1.3 percent in the amount of sunshine hitting the United States. Newsweek reported that the temperature decline, while relatively small in absolute terms, "has taken the planet about a sixth of the way toward the Ice Age average."

The big fear was a collapse of the agricultural system. In Britain, cooling had already shortened the growing season by two weeks. "[T]he resulting famines could be catastrophic," warned the Newsweek article. Some scientists proposed radical warming solutions such as "melting the arctic ice cap by covering it with black soot."

These days, of course, the threat is the opposite. The earth is no longer thought to be too cool but rather too warm. And black soot, rather than saving us, is seen as a chief villain. We have cast endless streams of carbon emissions skyward, the residue of all the fossil fuels we burn to heat and cool and feed and transport and entertain ourselves.

By so doing, we have apparently turned our tender planet into a greenhouse, fashioning in the sky a chemical scrim that traps too much of the sun's warmth and prevents it from escaping back into s.p.a.ce. The "global cooling" phase notwithstanding, the average global ground temperature over the past hundred years has risen 1.3 degrees Fahrenheit (.7 degrees Celsius), and this warming has accelerated of late.

"[W]e are now so abusing the Earth," writes James Lovelock, the renowned environmental scientist, "that it may rise and move back to the hot state it was in fifty-five million years ago, and if it does most of us, and our descendants, will die."

There is essentially a consensus among climate scientists that the earth's temperature has been rising and, increasingly, agreement that human activity has played an important role. But the ways humans affect the climate aren't always as obvious as they seem.

It is generally believed that cars and trucks and airplanes contribute an unG.o.dly share of greenhouse gases. This has recently led many right-minded people to buy a Prius or other hybrid car. But every time a Prius owner drives to the grocery store, she may be canceling out its emission-reducing benefit, at least if she shops in the meat section.

How so? Because cows-as well as sheep and other cud-chewing animals called ruminants-are wicked polluters. Their exhalation and flatulence and belching and manure emit methane, which by one common measure is about twenty-five times more potent as a greenhouse gas than the carbon dioxide released by cars (and, by the way, humans). The world's ruminants are responsible for about 50 percent more greenhouse gas than the entire transportation sector.

Even the "locavore" movement, which encourages people to eat locally grown food, doesn't help in this regard. A recent study by two Carnegie Mellon researchers, Christopher Weber and H. Scott Matthews, found that buying locally produced food actually increases greenhouse-gas emissions. Why?

More than 80 percent of the emissions a.s.sociated with food are in the production phase, and big farms are far more efficient than small farms. Transportation represents only 11 percent of food emissions, with delivery from producer to retailer representing only 4 percent. The best way to help, Weber and Matthews suggest, is to subtly change your diet. "Shifting less than one day per week's worth of calories from red meat and dairy products to chicken, fish, eggs, or a vegetable-based diet achieves more greenhouse-gas reduction than buying all locally sourced food," they write.

You could also switch from eating beef to eating kangaroo-because kangaroo farts, as fate would have it, don't contain methane. But just imagine the marketing campaign that would be needed to get Americans to take up 'roo-burgers. And think how hard the cattle ranchers would lobby Washington to ban kangaroo meat. Fortunately, a team of Australian scientists is attacking this problem from the opposite direction, trying to replicate the digestive bacteria in kangaroos' stomachs so it can be transplanted to cows.

For a variety of reasons, global warming is a uniquely th.o.r.n.y problem.

First, climate scientists can't run experiments. In this regard, they are more like economists than physicists or biologists, their goal being to tease out relationships from existing data without the ability to, say, invoke a ten-year ban on cars (or cows).

Second, the science is extraordinarily complex. The impact of any single human activity-let's pretend we tripled the number of airplane flights, for instance-depends on many different factors: the gases emitted, yes, but also how the planes affect things like convection and cloud formation.

To predict global surface temperatures, one must take into account these and many other factors, including evaporation, rainfall, and, yes, animal emissions. But even the most sophisticated climate models don't do a very good job of representing such variables, and that obviously makes predicting the climatic future very difficult. By comparison, the risk models used by modern financial inst.i.tutions seem quite reliable-but, as recent banking meltdowns have shown, that isn't always the case.

The imprecision inherent in climate science means we don't know with any certainty whether our current path will lead temperatures to rise two degrees or ten degrees. Nor do we really know if even a steep rise means an inconvenience or the end of civilization as we know it.

It is this specter of catastrophe, no matter how remote, that has propelled global warming to the forefront of public policy. If we were certain that warming would impose large and defined costs, the economics of the problem would come down to a simple cost-benefit a.n.a.lysis. Do the future benefits from cutting emissions outweigh the costs of doing so? Or are we better off waiting to cut emissions later-or even, perhaps, polluting at will and just learning to live in a hotter world?

The economist Martin Weitzman a.n.a.lyzed the best available climate models and concluded the future holds a 5 percent chance of a terrible-case scenario-a rise of more than 10 degrees Celsius.

There is of course great uncertainty even in this estimate of uncertainty. So how should we place a value on this relatively small chance of worldwide catastrophe?

The economist Nicholas Stern, who prepared an encyclopedic report on global warming for the British government, suggested we spend 1.5 percent of global gross domestic product each year-that would be a $1.2 trillion bill as of today-to attack the problem.

But as most economists know, people are generally unwilling to spend a lot of money to avert a future problem, especially when its likelihood is so uncertain. One good reason for waiting is that we might have options in the future to avert the problem that cost far less than today's options.

Although economists are trained to be cold-blooded enough to sit around and calmly discuss the trade-offs involved in global catastrophe, the rest of us are a bit more excitable. And most people respond to uncertainty with more emotion-fear, blame, paralysis-than might be advisable. Uncertainty also has a nasty way of making us conjure up the very worst possibilities. (Think about the last time you heard a b.u.mp in the night outside your bedroom door.) With global warming, the worst possibilities are downright biblical: rising seas, h.e.l.lish temperatures, plague upon plague, a planet in chaos.

It is understandable, therefore, that the movement to stop global warming has taken on the feel of a religion. The core belief is that humankind inherited a pristine Eden, has sinned greatly by polluting it, and must now suffer lest we all perish in a fiery apocalypse. James Lovelock, who might be considered a high priest of this religion, writes in a confessional language that would feel at home in any liturgy: "[W]e misused energy and overpopulated the Earth...[I]t is much too late for sustainable development; what we need is a sustainable retreat."

A "sustainable retreat" sounds a bit like wearing a sackcloth. To citizens of the developed world in particular, this would mean consuming less, using less, driving less-and, though it's uncouth to say it aloud, learning to live with a gradual depopulation of the earth.

If the modern conservation movement has a patron saint, it is surely Al Gore, the former vice president and recent n.o.bel laureate. His doc.u.mentary film An Inconvenient Truth hammered home for millions the dangers of overconsumption. He has since founded the Alliance for Climate Protection, which describes itself as "an unprecedented ma.s.s persuasion exercise." Its centerpiece is a $300 million public-service campaign called "We," which urges Americans to change their profligate ways.

Any religion, meanwhile, has its heretics, and global warming is no exception. Boris Johnson, a cla.s.sically educated journalist who managed to become mayor of London, has read Lovelock-he calls him a "sacerdotal figure"-and concluded the following: "Like all the best religions, fear of climate change satisfies our need for guilt, and self-disgust, and that eternal human sense that technological progress must be punished by the G.o.ds. And the fear of climate change is like a religion in this vital sense, that it is veiled in mystery, and you can never tell whether your acts of propitiation or atonement have been in any way successful."