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.

Out on the sand plains about 50 miles north of Minneapolis, there's a cluster of broken-down farmsteads that belong to the University of Minnesota. It's flat, unremarkable land, dotted with clusters of oak and pine, crossed by weedy, dead-end roads. Near a tin shed by the side of one of the trails, three circles of bare earth have been carved neatly into the stubbled grass. Each is divided into a grid of 6-by-6 plots that will soon be seeded with various sets of prairie plants--purple bush clover, butterfly weed, green coneflower, Indian grass.

By the time the plants come up next spring, a tanker truck will pull up here once a week, bearing pure carbon dioxide from a brewery. Researchers will fill a tank and pump high concentrations of CO2 over two of the three circles, using a sensor to make sure the level stays constant at about 150 percent of what it is now. The third circle will be left alone for comparison. The point is to find out how the plants grow in the enriched air, and whether diverse plots do any better than monocultures. It's a neat little study.

It is also an experiment inside an experiment. For a century and a half, humanity has been adjusting carbon dioxide in the atmosphere upward about 25 percent, bringing it to a level higher than it's been any time in the last 150,000 years. Now the results are starting to come in.

Over the past century the globe has warmed up about 1 degree, and the oceans have risen an inch. Ice is melting at the poles and atop mountain ranges. Droughts and floods are becoming more common. The very timing of the seasons has shifted; spring now comes a week earlier to the Northern Hemisphere than it did in the 1950s. Plankton has been dying in the ocean off California; bugs and plants are moving north or uphill; the Arctic permafrost is thawing; and strange things are happening with the El Niño system of ocean currents.

Global climate change, global warming, the greenhouse effect, whatever you name it, is no longer a controversial theory or even a worrisome prediction. With little fanfare, and considerable reluctance on the part of many researchers, it's become expert consensus. How much further to push the global experiment is a matter politicians from around the world are supposed to decide later this year. But the change already set in motion will continue at least until the children of children born now are old. What this means for the planet--20 years, 50 years down the road--is the question researchers at the UM's prairie site and elsewhere are trying to answer now.

You've heard the basic greenhouse explanation. It's like leaving your car out in the sun. Light comes through the windows at a certain wavelength; bounces off the interior; and can't get back out because of its new wavelength. Similarly the stratosphere--the layer of air some nine to 31 miles up from where we live--is less "transparent" to radiation bouncing off the globe's surface than to that coming in from the sun. Without this natural greenhouse, Earth's average temperature would be around 18 below.

The substances chiefly responsible for the greenhouse effect are water vapor, methane, and carbon dioxide. And since humans began vaporizing the world's coal mines and oil deposits around the mid-1800s, they've added billions of tons of CO2 to the atmosphere.

This much is basic physics. What was disputed, until recently, was whether those additions enhanced the natural greenhouse effect or simply blended in without further consequence. (One caveat: Though often confused, the greenhouse effect is not the same as the ozone-hole problem. In fact, they work somewhat at cross-purposes. Ozone deterioration, caused by chemicals until recently found in air conditioners, spray bottles, and styrofoam, allows more ultraviolet radiation to hit the surface of the earth, causing skin cancer and other problems. But thinning ozone makes little difference in terms of temperature; it could even help cool the globe, much as a fraying blanket would send you shivering at night. Just to make things more complicated, the chemicals that destroy ozone do also serve as greenhouse gases, probably canceling out the cooling effect right there.)

The jury appointed to answer the global-warming question was the Intergovernmental Panel on Climate Change, a body of 2,400 scientists set up by a United Nations conference in 1987. Its membership was drawn from the world's most illustrious research institutions; the U.S. delegation alone hails from places like the Lawrence Livermore National Labs, Harvard, MIT, and the Woods Hole Oceanographic Institute. The IPCC has released two "global climate assessments"; each ran thousands of pages, with footnotes enough to fill another volume. But if the first report was comparatively inconclusive, the second, published in 1995, was a bombshell.

First, the IPCC said in the 1995 report, its earlier findings (the 1-degree increase in global temperatures over the last century-plus, the 1-inch sea-level rise, and many other slight, but increasingly noticeable trends) had been confirmed by additional research. But, it added as it did in 1990, such trends in themselves didn't mean much: Global temperatures have fluctuated up to 10 degrees over geologic time, usually triggered by shifts in the earth's orbit around the sun. And though the most recent warming started right after fossil-fuel burning took off, that didn't prove a causal relationship. What led the IPCC to conclude that such a relationship did exist was a scientific breakthrough no one had expected for at least another decade or two: The computer models had fallen into place.

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