The Forecast: Hazy and Puzzling

In its Planet of the Year issue (Jan. 2), TIME highlighted numerous threats to the earth's environment. The magazine will continue to pursue that story, covering new developments and actions taken to solve ecological problems. This is the first of our follow-up reports:

Is the earth warming up or not? Many scientists say it is, thanks to the greenhouse effect, the heat-trapping property of gases that pollute the atmosphere. Some computer studies indicate that the warming could cause more frequent droughts and eventually produce a major climatic upheaval. Others say, not necessarily: increased cloudiness and other mitigating phenomena could counteract the warming before it has significant effect.

Last week the naysayers appeared to pick up a bit of ammunition in the continuing debate. A study by the National Oceanic and Atmospheric Administration published in the journal Geophysical Research Letters shows that the climate in the 48 contiguous states of the U.S. has remained pretty much unchanged for nearly a century. By analyzing data gathered at weather stations across the U.S. between 1895 and 1987, meteorologist Kirby Hanson and two NOAA colleagues found that the average annual temperature had fluctuated between 52 degrees F and 54 degrees F, with no statistically significant long- term trend either up or down. The same was true of average rainfall, which generally ranged from about 33 in. to 36 in. yearly.

At first glance, the study would appear to be a serious blow to the greenhouse theory. Not so. The U.S. makes up only 1.5% of the earth's surface, and the country's temperature trends are not necessarily indicative of what is taking place on the planet as a whole. James Hansen, head of NASA's Goddard Institute for Space Studies and one of the most prominent proponents of the greenhouse theory, was not at all swayed by the new study. "Even in a warming world," he says, "you'd still expect on a statistical basis to see local variation -- one region cooler than the average, another hotter. If you look at an area as small as the U.S., then natural variability is very large. But % it's the global average that is important." While other climate experts are slower to make concrete predictions, Hansen's studies of global temperatures suggest that the warming trend has already begun and will soon become widely apparent. Warns the NASA scientist: "Our model predicts that by the middle of the 1990s, the greenhouse effect should be pretty clear not only to scientists, but also to the man in the street."