Sharon Begley

Averages don't mean much to Jacques Couture, 47, whose family has been tapping Vermont's sugar maples "back to the 1700s, I think," he says. Sure, he's been hearing for years how some nasty-sounding thing called the "global mean temperature" is expected to rise in the coming decades. Couture figures that will bring nothing more worrisome than a couple more warmer days in August. But means, or averages, can hide great calamities. As the world warms, the climate belts most suitable to particular plants will shift toward the cooler poles. And nights will heat up even more than days will. "You need the cold nights for good sap flow," Couture says. The sugar-maple belt, which now dips into Tennessee, could contract like concrete in the cold, moving farther into Canada. Any trees still south of Maine might not have the cold spring nights needed to make their sap run. On the ledger sheet of global warming's winners and losers, count Couture, or his grandchildren, as potential losers.

Alan Johnson, president of Hudson Bay Port Co. in Churchill, Manitoba,employs 80 dockworkers to load 500,000 tons of grain into container ships. But the men work only from July to October. Before and after, sea ice blocks the bay. The hiatus doesn't do much for the local economy. But global warming might help. The planet, say computer climate models, should heat up the most near the poles. Churchill is about as close to the North Pole as you can get without running into elves. If the world warms, Churchill will be open for business more weeks every year. "The past few years," Johnson said in November, "the season seems like it's been longer. We still have open water now." Put Johnson, and northern ports, in the potential winners' column.

For more than a decade climatologists have been sounding the alarm: the continued release of "greenhouse gases" will almost certainly warm the world. Average annual temperatures for the earth's surface are already up 1 degree Fahrenheit in the last 100 years. And the pattern of warming--more in the Arctic than near the equator, more in the night than the day, more in winter than summer--fits that predicted by computer models of man-made climate change better than it does natural climate variability. Such findings spurred the United Nations' Intergovernmental Panel on Climate Change--some 2,500 scientists from academia, environmental groups, industry and government from more than 150 nations--to conclude, in 1996, that man-made warming has already been discerned. Last week the British Meteorological Office announced that November 1996 to November 1997 was the hottest year on record.

And more is on the way. Gases such as carbon dioxide (from deforestation and the burning of coal, oil and natural gas) act like little panes of glass in a greenhouse. With nations pouring at least 7 billion tons of carbon into the atmosphere every year, there is 30 percent more carbon dioxide in the air today than in 1860. (How do scientists know? They analyze pockets of air trapped in ice cores. Then they determine the age of the core by counting layers of ice deposition, much like counting tree rings.) So much warming is built into the atmosphere already that the planet will heat up another half degree in the next 20 years. That's why 160 nations meeting this week in Kyoto, Japan, will try to reach some kind of agreement on what to do about greenhouse emissions. But there's no way to undo the past. "Even if we are wildly successful in Kyoto," says Richard Moss of the IPCC, "we are in for a doubling of carbon dioxide by the middle of the next century."

If that happens, we could see the ultimate good news/bad news scenario. Heating bills will go down. That's good. But more people will die of heatstroke, as 465 Chicagoans did during a July 1995 heat wave. That's bad. Longshoremen in northern ports will work more days every year. That's good. But dengue fever, now confined to the tropics, may reach Winnipeg. And rising sea levels will obliterate more than 3,000 square miles of Louisiana coastline and wetlands. Both bad.

These forecasts illustrate the hidden power of the deceptively small temperature changes that climatologists expect. The IPCC warns that the world could be, on average, 1.8 to 6.3 degrees warmer by 2060. But some regions will warm much less and others, especially the interiors of northern continents, will warm much more. (That's how you get an average, after all.) The United States is facing a temperature rise of 5 to 10 degrees by 2060, with 10 to 30 percent less moisture in the ground during the summer growing season. And small temperature increases "become amplified when you run them through biological systems," says Daniel Hillel of the University of Massachusetts. The eggs of freshwater fish, for instance, are exquisitely sensitive to temperature. With a rise of 6 degrees, brook trout would be unable to live in more than half their southern Appalachian streams. Too bad for local anglers. Smallmouth bass and yellow perch, though, would expand their range across Canada by 300 miles. Fishermen there would come out winners.

Those are the kinds of regional effects that researchers and policymakers are now trying to forecast. Last month more than 400 scientists, economists, physicians, resort owners, fishermen, farmers and business people met in Washington to discuss how global warming could affect everything from ski resorts in Vermont to oystering in Puget Sound. And this week in Kyoto, the IPCC will distribute a 600-page report on how climate change will harm, or help, specific regions worldwide. At the end of a paragraph listing all sorts of "potentially irreversible" adverse effects, the report acknowledges that "some effects of climate change are likely to be beneficial."

For every 1.8-degree rise in average temperature, heating bills will fall 11 percent in the United States. Winners: people in northern towns like Green Bay, Wis., who will also save on snow-removal costs. But frigid temperatures have kept land in the Alaskan and Siberian Arctic as hard as rock. Now the permafrost in both places has begun to melt to the consistency of New England clam chowder. Alaskan towns are already spending up to $3 million to shore up every mile of sinking road. Another loser: Glacier National Park (1995 tourist spending: $80 million), all of whose glaciers, absent a miracle, will be gone by 2030.

Since what will happen to the world overall is still uncertain, what will happen to a particular region is even iffier. But one outcome--sea-level rise--is a pretty sure bet. Unlike weather, sea level does not depend on clouds, chance or mischievous jet streams. And it is already happening: seas have risen by almost 10 inches this century, and more thermal expansion of seawater and glacier melting will push oceans up even farther. IPCC calculation: 23 inches by 2100, half that by 2050. The United States could lose 10,000 square miles of coastland with a two-foot sea-level rise. Smith Island in Chesapeake Bay, home to an isolated community that still speaks in the Elizabethan lilt of their ancestors, may disappear beneath the waves. Sandy beaches in Monmouth County, N.J., and on New York's Long Island slope so gently that a sea-level rise of only one foot--likely by 2050--will inundate 100 feet of beach. One third of the Everglades sits less than 12 inches above the Atlantic; since the resident and rare Florida panther is not known for its breaststroke, it will face extinction. Still, communities can save shorefront developments by building sea walls. Much of New Orleans, and San Jose and Long Beach, Calif., are already below sea level, but they are still inhabited cities and not Atlantises. To protect Manhattan's 29-mile waterfront from a one-foot rise would cost just $30 million. Winner: construction crews.

But sea walls are no panacea. In Puget Sound, an additional sea-level rise of 14 inches will turn 40 percent of the mud flats, where shellfish spawn, into ocean floor, where they can't reproduce. Residents of Camden, N.J., and farmers in the central part of that state may find that the aquifer that supplies drinking water and irrigation has become brackish because rising seas push saltwater farther up the Delaware River, which recharges this aquifer. Miami's Biscayne aquifer is similarly vulnerable to such "salt intrusion." Winner: sellers of bottled water. Losers: farmers, who can't use saltwater on their crops ... and can't afford Evian for them, either.

Cathy Gill runs a commercial marina with her husband in Crystal River, on Florida's Gulf Coast. "We've heard all about" global warming, she says. If seas rise 10 inches (at the low end of projections for 2050), the waters will inundate enough of the Louisiana wetlands--where brown shrimp spawn--to slash the shrimp catch in the gulf by 25 percent. Add shrimpers to the list of potential losers in the greenhouse sweepstakes. But fishermen off Los Angeles are now hooking expensive yellowfin tuna thanks to warmer Pacific waters, like those brought by El Nino. In a warmer world, suspects climatologist Kevin Trenberth of the National Center for Atmospheric Research, El Ninos will be more common. Put southern-California fishermen on the list of potential winners.

If the world warms by even a few degrees, tropical diseases could follow the rising mercury. Once again, it is a specific quirk of global warming, not the global average, that poses the greatest threat. Nighttime temperatures will increase more--perhaps 10 percent more--than daytime temperatures. Winter readings will rise more than summer ones. Greenhouse skeptics see this as another sign that global warming will be benign; if the nights, which are naturally cooler than the days, are a little warmer than they are now, who will notice? And if winters are a bit balmier, bring it on. Except for one thing. Because nighttime and wintertime cold kills insects and their eggs, temperature determines how far from the equator tropical pests can survive. Mosquitoes that carry malaria cannot stand more than a few days below 62, explains Paul Epstein of Harvard University. Today that thermal barrier keeps malaria out of regions where 58 percent of the world's population lives. If the world warms 5 to 9 degrees, estimates the IPCC, 60 percent of the population will live in the malaria zone.

Some disease microbes have already benefited from climate change. Beginning in the late 1980s, the American Southwest experienced six years of drought. Populations of predators such as owls, snakes and coyotes fell. Then, in 1993, the spring rains fell in buckets. Pine nuts and grasshoppers flourished. Deer mice, which eat pine nuts and grasshoppers, exploded in number. The deer mice harbored hantavirus, which makes victims feel like they have the flu but can cause hemorrhaging, kidney disease and death from respiratory failure. Floods drove the mice from their burrows. They bit people; five died. "This pattern of drought and flood is what the climate models predict," says Epstein, "so we could be in for more outbreaks like this."

Agriculture is another crucible of climate change. Mark Wilcox's family has been farming the rolling plains of Saskatchewan since 1903. Winters are rough and long, with temperatures dipping below minus 40 for weeks at a stretch. "Whoever can leave for the winter, does," says Wilcox. But the cold weather has been good to Wilcox's wheat, the hard, low-gluten durum variety that millers turn into high-quality pasta flour. Wilcox, if he can coax greater yields from his 2,240 acres as global warming brings him more frost-free days and a longer growing season, could pick up customers from farmers to the south who can no longer grow durum wheat. "If they grow less," says Wilcox, "what is produced will be at a premium, and that'll help us, price-wise." Put Wilcox in the potential winners' column. Similarly, the hard, red winter wheat of the southern plains requires persistent winter cold to set flowers. In a greenhouse world, farmers in Oklahoma and Texas might be able to grow only low-quality, low-price spring wheat. They would be agriculture's losers.

How a warmer world will affect food production is one of the most complicated--and important--questions in the debate over warming. Skeptics argue that a worldwide greenhouse will be as beneficial to crops as an artificial greenhouse. In a warmer world, for one thing, growing seasons will be longer. In the northern temperate region, they are already eight days longer than just 11 years ago. And in a world richer in carbon dioxide (which plants "breathe" in), crops should grow larger faster. The IPCC optimistically notes that, "on the whole, global agricultural production could be maintained regional effects would vary widely."

That "but" conceals a lot of potential pain. Warming will shift climate belts toward the poles, and toward higher elevations, where it is cooler. Plants are already "climbing" the Alps at roughly 12 feet per decade. (Plants don't actually pack up their roots and walk to cooler climes, of course: shifting climate zones just changes where seedlings are able to take hold, and where mature plants die off.) That's why Wilcox could win while some farmer in Oklahoma could lose. Also, crops differ in how they respond to extra carbon dioxide. Wheat, rice and soybeans suck it up, and grow faster. Corn and sugarcane don't respond much. Other things being equal, farmers of the first three crops will win; farmers of the others might manage only a draw.

Warmth may seem like natural fertilizer, but "in fact all plants are adapted to an optimal temperature," explains Cynthia Rosenzweig of Columbia University. "Even Florida citrus yields could fall 30 percent if mean temperatures rise several degrees." Corn dies if temperatures reach 95 while the plant is flowering. And in a warmer world with more evaporation, the frequency and severity of dry spells in drought-prone regions may well increase. In the Central Plains, droughts could strike every other year by 2050. Thirsty corn and soybeans might fail in the Southeast and Great Plains but thrive farther north. "Some farmers will be net winners but others will be net losers," says UMass's Hillel, coauthor with Rosenzweig of the forthcoming book "Climate Change and the Global Harvest." "Florida's orange-crop loss may be South Carolina's gain."

Warmth that's good for crops is also good for crop pests. A longer growing season could, for example, enable grasshoppers to squeeze in another round of reproduction. Weeds and crop diseases will also thrive in a warmer world where fewer regions experience the harsh winters that keep pest populations in check. "All indications are that pests, and diseases like rusts and molds, will increase," says Linda Mearns of NCAR. In the United States and other affluent countries, farmers will likely adapt. They will irrigate more, fertilize more and apply pesticides more. But adaptation is expensive, and can go only so far. "The climate is going to be in continual change," says NCAR's Trenberth. "I'm not sure people realize this. Inability to plan may be worse than the changes themselves."

Living things that don't have farmers looking out for them may meet with a more dire fate. Kirtland's warbler, an endangered bird that nests exclusively under young jack pines in northern Michigan, faces a grim future: with more heat and less rain, jack pines there will likely die off in the next 30 to 90 years. So, therefore, may the warbler. Populations of Adelie penguins in the Antarctic Peninsula have fallen 40 percent in 22 years; midwinter mercury readings around the AdElie's home are up a huge 8 or 9 degrees in the last 50 years, melting the sea ice where the Adelie's food--shrimplike krill--lives. Bird lovers' greatest concern is the 1 million-plus sandpipers, red knots, ruddy turnstones and other birds that make a fuel stop at Delaware Bay during their spring migration to the Arctic. The birds' stop coincides with the emergence of horseshoe crabs, triggered by the full moon, from the ocean. The birds eat the newly laid crab eggs. But if the birds take wing from their wintering grounds earlier, because spring arrives earlier, then they will pass over the Delaware before the crabs emerge. In that case they would miss the caviar banquet, and be too low on fuel to reach the Arctic.

Things will get really interesting if the changes global warming brings are not incremental but sudden. One place vulnerable to abrupt change is the Atlantic Ocean current that brings warm water from the Sargasso Sea to Britain. The driving force behind the current is salty water that sinks when it gets cold, at its northern terminus. Like a grocery-store conveyor belt, the sinking of one end draws the rest of the belt forward--in this case, northward. But if the oceans warm enough, the water will not sink. The current would shut down, explains Wallace Broecker of Columbia University, with "consequences could be devastating." Dublin would have the climate of Spitsbergen, Norway, as the collapse of the current makes temperatures in Western Europe plunge 20 degrees in 10 years. Loser: European agriculture.

It shouldn't be surprising that climate change will produce some winners. After all, roofers in south Florida cleaned up after Hurricane Andrew, as do construction crews in California after earthquakes. But climate change will almost surely bring more losers than winners. Some losers will be able to buy a reprieve--New England ski-resort owners, faced with a shorter season, can dump man-made snow on their slopes, and governments can take steps to control tropical diseases, whose spread depends as much on public-health measures as on where pests can live. But such adaptations are expensive. And you can't write a check to bring back melted glaciers. The debate in Kyoto will focus on how much it will cost the world's economies to burn less coal, oil and gas. Now scientists are coming to understand who will lose if we don't.

In the poll, 11% say global warming would be 'disastrous' for today's adults while 29% say it would be that bad for today's children when they're grown.