The Hot Zone

Global warming isn't just a theory anymore. Now the arguments are about how dire the changes in world climate will be, how soon they'll come--and what, if anything, can be done to moderate them.

And that's just the story of the North--which, according to the models, is in for a much better time of it than the Southern Hemisphere. For much of Africa and Latin America, the models forecast average temperature increases up to twice as high as those of North America, Europe, and much of Asia. That means more droughts for parts of the world that already suffer from chronic water shortages. A mild shift in monsoon patterns could wipe out entire regions where farmers barely get by now. This is known as the "green north-brown south" pattern; the consequences for migration alone are staggering.

There are, however, two great equalizers: the oceans and the bugs. Both have ways of evading containment, and neither is very well understood. Ocean waters are slower to react to atmospheric changes than the air. But they have, the IPCC reported, been getting warmer. That may have caused the 70-percent die-off California researchers discovered two years ago among the tiny sea organisms called plankton. And if plankton is in trouble, so are the fish that eat it--as well as the 30 percent of humanity that rely on fish for food and agricultural fertilizer. (Closer to home, a University of Minnesota biologist estimates that at the predicted rate of warming, something like 40 percent of the walleye and northerns could disappear from the lake country.)

Tropical storms--hurricanes, typhoons, cyclones--by contrast, like warm water. They don't even form in places where the surface temperature isn't at least 78 degrees. Researchers aren't far enough along with the models to say for sure that global warming will bring more storms, but the insurance industry has been taking notice.

Meanwhile, on mountain ranges from the Rockies to the Alps, glaciers have been pulling back, in some places as fast as 100 feet or more each year. In Austria, the retreating ice exposed the body of a man who'd tried to cross the mountains the last time the glacier was this small--before the Roman Empire. Melting ice, along with the fact that warm water expands, is the most likely explanation for the last 100 years' ocean-level rise. And there's more to come: The IPCC projects that if current trends continue, the seas will rise 12 inches by 2050, flooding most of the East Coast's beaches and up to one-fifth of countries like Bangladesh and the Netherlands.

As for the bugs, first the good news: Researchers expect that as climate warms, fewer people in North America and Europe will die of cold-season illnesses, including flu. Most of the rest of humanity's predators, however, stand to see global warming as a boon. Right now, about 45 percent of the world is suitable habitat for the mosquito that carries malaria. With a 5-degree average warming, the insect could expand its range to 60 percent of the globe, reaching upland mega-cities like Nairobi, Kenya and Harare, Zimbabwe, as well as to a good part of the central United States. In the past few years, the mosquito has been found 1,700 feet up on Latin American mountains where it never used to climb above 1,000 feet.

Similar projections apply for the bug that carries dengue hemorrhagic fever, an illness that starts with headaches and ends with fatal internal bleeding. It, too, has been moving north and uphill, bringing an epidemic that began in Argentina to much of Mexico and into the States. Hantavirus, which has killed 60 people in the United States since it appeared in the Southwest four years ago, was handed outbreak conditions by a series of odd-weather years in which mice multiplied.

The world's lead killers, waterborne microbes, also thrive in warmer waters, and they love to be sloshed around by floods. The Third World, where 6 million children already die each year for lack of clean water, will feel the consequences first. But Los Angeles, Phoenix, and Miami also know what it means to be water-starved; even Minneapolis has reason to consider the effects of pollution and microbes in the Mississippi River water it drinks.

And that's only the devil we know. It doesn't take much to figure out that as weather conditions push plants and animals to their limit, new diseases are likely to be carried out of the interiors of forests; or that climate stress, like any other kind, can weaken the immune systems of humans, plants, and animals, making them more susceptible to disease just when they can least afford to be. Perhaps, some public-health researchers figure, it will be disease that finally puts global warming front and center.

Beyond all the predictions, though, one more great unknown lingers. Wily as it seems, climate is actually an astonishingly balanced system. Winds work to even out air temperatures between the poles and the tropics. Plants and tiny mollusks store carbon that would otherwise float in the atmosphere. The oceans swallow massive amounts of heat and move it around, with pachydermal speed, in currents larger than all the world's rivers put together.

But just as those forces balance each other, they can also feed on each other. Feedback crescendos, researchers believe, are what caused past climate "flips," in which the globe switched from one state of relative equilibrium to another--not, as it used to be thought, in millions or even thousands of years, but in as little as a few decades. That's what happened some 11,000 years ago, during an event called the Younger Dryas--a kind of climatic hiccup at the end of the last Ice Age. Meltwater from the shrinking glaciers diluted salty ocean waters and set off a chain reaction in the way warm and cold water masses moved around. In a nutshell, the Gulf Stream that keeps northern Europe comfortable took an unpredictable turn, and glaciers returned to much of the continent. And in Minnesota, mammoth and mastodon disappeared as the forests they roamed became deep freezes.

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