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.

Granted, the people of those times may have been more susceptible to climate change than we (at least those with air conditioners and food supplies carted in from thousands of miles away) are now. But from what's known so far, average temperature is just the start of global climate change--or, as many researchers prefer to call it, just plain "global change."

To start with, there is a nasty rule that says a slight increase in the average means an exponential rise in extremes. If Minneapolis/St. Paul get only a little warmer, days with a "heat index" of 95 degrees or more--the kind that can kill the old, the young, and the sick--could come four times to 10 times as often.

If flooding becomes just a little more common, extreme floods increase that much more; a 100-year-flood plain can become a 10-year-flood plain. The same goes for 100-year droughts, and so on.

One of the reasons why researchers now speak of "global climate change" rather than "global warming" is that warmer temperatures change the way air and precipitation move. Minnesota, as it happens, sits at the intersection of three major climate forces--warm, moist air from the Gulf, winds from the West, and the Alberta clippers. A slight shift in one or all of them could bring anything from a little extra snowfall to a new tornado alley. Stanford University climatologist Stephen Schneider calls the region "ground zero of climate change" for precisely that reason.

As climate shifts, so do the boundaries within which plants and animals can live. University of Minnesota researchers have been studying samples drilled from deep lakes and forest floors for traces (plant pollen, fossilized fly wings, ash from prairie fires) of eras long gone. They've found that through geologic time, trees like spruce and oak have pulsed back and forth across the region, crossing vast territories in pursuit of favorable climate; in fact, the forests growing here now may have evolved precisely in response to constant climate change at the glacial boundary.

But those changes were gentle compared to what's down the road. Margaret Davis, a University of Minnesota regents' professor in ecology, says even at their fastest rate, the trees she studied moved no more than two-thirds of a mile per year. Under current climate projections, "we're asking them to go about ten times that fast. And I fear that a lot of species won't be able to keep up."

How exactly the landscape will change is hard to forecast. UMD's John Pastor has run calculations which suggest that at the IPCC's projected rate of warming, spruce, maple, birch, oak and pine could all but disappear from sandy soils in northern Minnesota. There's nothing unduly apocalyptic, the data indicates, in envisioning parts of Voyageurs National Park and the Boundary Waters, which now make up the southern edge of the "northern boreal forest," as landscapes of stumps.

Dying forests, of course, would be at much greater risk of burning. The Canadian Forest Service has found that forest fires were up almost fourfold in the mid-1990s from a decade earlier; Minnesota, too, has seen a record number of blazes. Fires, in turn, release carbon the trees have heretofore been storing--more greenhouse-enhancing CO2.

And don't forget the peat bogs that cover much of the Arctic and chunks of northern Minnesota. They contain, says UM regents' professor Eville Gorham, about one-third again as much carbon as there is in the world's atmosphere now. Even a slight warming could cause many peat bogs to dry up and release CO2; or the permafrost below some of them could thaw and release another potent greenhouse gas, methane. In a worst-case scenario, vast tracts of peat could catch fire, smoldering for years at a time in what Gorham calls the "Kuwait of the North."

But the plants of most immediate concern in global-warming scenarios are agricultural crops. There are those who argue that there's nothing to worry about. Avowed "climate skeptic" Sherwood Idso notes that CO2, besides warming the atmosphere, serves as an airborne fertilizer. Thus, humans should celebrate fossil-fuel burning--because it heralds a "rebirth of the biosphere," the return to a "paradise lost" of lush growth.

Most ag researchers are not so sure. Aside from the matter of how long crops could sustain a CO2-induced growth spurt, changed weather patterns are almost guaranteed to affect production. Crop failures are likely in portions of the world's corn belts as rains fail to show or heat spikes wilt crops. As far back as 1988, the U.S. Environmental Protection Agency calculated that crop acreage in the Midwest could decline by 25 percent under the global-warming projections of the time. In one scenario, a string of severe droughts could turn Kansas into a desert in as little as a decade. What's more, warmer temperatures bring better conditions for pests, from grasshoppers to corn borers.

There is an easy answer: Farming will just have to move north. It looks a lot less attractive when you consider the upheaval involved (ask any small town in southern Minnesota). Nor is it clear that the sandy soils of, say, northern Minnesota and Alberta could perform the way the Central Plains' deep-down black dirt has. And even if it all works out, a transition period of dicey harvests could be bad news at a time when the world's food supply looks increasingly uncertain.

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