Weather: a new period of extremes?

So you think today's weather is unusual and the climate must be changing? Well, you just might be right. But, then again, you may be wrong. As any "old-timer" can tell you, with weather the unusual is unsual. This makes it extremely difficult to determine whether or not the climate is changing.

But climatologists are as interested in this question as the person digging out after a record snowfall or the survivor of an unprecedented heat wave.

In the early 1970s some of the scientists studying world weather patterns became convinced that the climate was changing. Weather patterns, they proposed , would become more variable, with more severe winters, summer heat waves, and droughts.

Ten years later, this remains a hotly debated theory. And the recent spate of severe wintes, hot spells, and apparently abnormal weather conditions is adding new fuel to the scientific argument.

Although the basic question has not been answered yet, the scientists have come up with some climate insights. One is that the period from the end of the Dust Bowl days in the 1930s to the mid-1970s was remarkable in a number of respects.

"It was a long, lucky period as far as agriculture goes," observes Steven Schneider of the National Center for Atmospheric Research (NCAR) who is intensively studying the relationship between climate and agriculture. It was a period in which temperature and rainfall patterns were significantly less variable than has been the case historically.

"It's been worse since the mid-1970s," Mr. Schneider adds.

In 1979, Thomas Chico and William D. Sellers of the University of Arizona analyzed annual temperature variability in the US since 1896. They found that the temperature varied considerably more from 1900 to 1930 than it did from 1930 to 1970. The greatest decrease in variability was in the Midwest and was due primarily to milder and more uniform winters.

"This variability hit its lowest point in the early 1970s. From that period on, it's very hard to tell," says Professor Sellers. Although no one has yet done the painstaking research required to look at what has happened in the last five years, a number of experts do feel that the pattern of the recent past has been broken.

While cautioning that each year has its major weather "anomaly," Robert Livezey, a research meteorologist with the National Weather Service (NWS), observes, "We appear to have broken with the trend of the last 40 years."

To find two extremely cold winters back to back comparable to those that the Eastern United States experienced in 1976-77 and 1977- 78, weather experts have to go back more than a century to 1855-56 and 1856-57. Last summer's heat spell in the Southwest was the worst since 1957.

On the other hand, the droughts in the 1970s were rather mild, historically speaking.

A return to the more extreme weather patterns of the past could have serious implications for US society. For several years now, Steven Schneider of NCAR has been arguing that modern US agriculture has not yet been tested by unfavorable weather patterns that can be expected sooner or later. In his book, "Genesis Strategy," Mr. Schneider argued that we must store up adequate food reserves in years of plenty for the lean years that are sure to follow.

Such an outlook affects weather-dependent enterprises besides agriculture. The skiing industry is an example. So far, this winter has been warm and dry over most of the US West. As a result, most Western ski areas do not have an adequate base of natural snow.

However, "most of the Western ski areas learned a valuable lesson from the 1975-76 drought. They bought snowmaking equipment. As a result, 26 out of the 32 areas in Colorado are open, at least on a limited basis," reports debbie Dix of Colorado Ski Country.

In addition, ski resorts such as Vail and Aspen, Colo., are trying to diversify. They are putting in other types of recreational facilities and trying to attract people year-round.

Lack of snowpack in the eastern Rockies, last summer's heat wave, and below normal autumn rainfall is causing problems now for traffic on the Mississippi River. Low water has resulted in barges going aground, and some areas of the river have been at least temporarily closed to commercial traffic. According to Clarence Vicroy, a regional hydrologist for NWS, the upper Mississippi may reach record low levels unless there is major precipitation in its drainage within the next month.

"It's shaping up as very, very bad . . . both for the short range and the long term," Mr. Vicroy says.

If dry conditions hold through the spring, farmers in the region may face shortages of irrigation water.