From the Editors8 Scientific American August 2000

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Global warming tends to inspire great huddles of pessimists and smallergaggles of optimists. Happily, each faction can find grist for its mill in anew government report from the U.S. Global Change Research Programthat projects how warming trends will affect this country. A draft of the

report is being posted for commentary on-line at www.gcrio.org/NationalAssessment/as this magazine goes to press.

According to the report’s authors, climate models suggest that temperatures in theU.S. will rise on average five to 10 degrees Fahrenheit (three to six degrees Celsius)over the next 100 years—a larger increase than the rest of the world will generallysee. The effects will vary from region to region: over much of the country, rainfalland humidity should increase, but the southeasternstates might get hotter and drier. Flooding may be morewidespread, but perversely, so too might drought, be-cause water management grows more complex as win-ter snowpacks in the mountains recede.

Western deserts could give ground to shrublands.Some ecosystems, such as vulnerable coral reefs oralpine meadows, could disappear. Fortified by highercarbon dioxide levels in the atmosphere, forests mightflourish, at least over the near term, but with a shiftedmix of tree species. We humans, meanwhile, will proba-bly contend with coastal flooding and other disruptions.

Conversely, the new hothouse con-ditions could benefit agriculture. Thegovernment report is optimistic aboutthe potential of farmers to adapt tochanging climates and to raise cropproductivity. For a world that dependsso heavily on U.S. grains and other foods, this is good news. But the changes may notentirely be a boon for the farm belt: not all regions or crops would gain equal advan-tage, and farmers may suffer in an economic climate of more fierce competition andsurplus. Nor does anyone yet know precisely how the pest populations could eventu-ally cut into this boost in agricultural and natural productivity.

Scant discussion in the report goes to warming’s effect on disease, which publichealth specialist Paul R. Epstein addresses in his article beginning on page 50.

Tropical diseases such as malaria may become uncomfortably more familiar to thoseof us in the currently temperate zone. Although outbreaks such as New York’s brush-es with West Nile virus cannot be attributed to climate change, milder winters thathelp pathogens or their hosts survive make these events increasingly probable.

One of the best things to be said for the report is that it emphasizes how uncertainthe course of global warming and its repercussions will be. Much depends on exact-ly how high and how quickly the temperature rises. Global warming’s doubters liketo emphasize the crudeness of even the best climate models, and they are right to doso. But the preponderance of evidence points to hotter days to come, which makesit only prudent to assess what the potential costs might be.

E D I T O R _ J O H N R E N N I E

If You Can’t Stand the Heat . . .

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Pessimists and optimists canboth find vindication in a new

report on climate change.

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