Weather: Prediction and Control

An old North Woods Indian known for his accurate weather forecasts was once approached by a newspaper reporter who inquired how he could tell that the coming winter would be a cold one. Gesturing toward the cabins of his neighbors, the Indian replied: "White man make big wood pile."

The story, told frequently down in Maine, is doubtless apocryphal. But it reflects the fact that despite modern instruments and meteorological methods, weather forecasting of any kind remains at best an inexact science. Dreams of actually doing something about the weather are equally unrealistic. People pausing to rest as they shovel out from under this winter's snows or shivering in chilled homes may look longingly toward a day when science will be able to make weather to order. Was the Big Freeze really necessary? Answer: alas, yes. Despite some limited successes in making it rain on demand, most scientists believe that, for the foreseeable future, weather modification is unlikely.

Wrathful God. What is likely is that the weather, as it has done throughout history, will continue to toy with its would-be forecasters, embarrassing them with rain when they call for clear skies, drought when they predict precipitation. Indeed, the weatherman's plight will probably not change a millibar from that described by the English meteorologist Sir Napier Shaw. Wrote he: "A forecaster's heart knoweth its own bitterness, and a stranger meddleth not with its joy."

The ancients believed that weather changed at the whim of the gods, and Homer's Odyssey contains several references to storms raised against Odysseus by a wrathful Poseidon. Modern-day meteorologists have established that earth's weather stems mainly from the sun. Each day radiation equal to some 17 trillion kilowatts reaches the earth's atmosphere from the sun and warms the planet, particularly around the equatorial regions, where this radiation strikes more directly than it does at the poles.

Heated tropical air rises and flows from the equator toward the colder polar regions, while cold polar air flows toward the equator. The planet's eastward rotation skews the movement of air and causes the prevailing westerly winds that blow from North America toward Europe, and roar across the southern oceans. Topographical features, such as land masses and mountains, and uneven heating patterns further alter the air flow. The result is the assortment of high-and low-pressure regions and the winds that give the earth its weather.

Forecasting the weather has long occupied man's attention. Early farmers and sailors, whose livelihoods--and sometimes lives--depended upon the weather, learned by experience how to read the signs that frequently presaged change. Sailors realized from early days the general wisdom of the poem "Sky red in the morning/ Is a sailor's sure warning/ Sky red at night/ Is the sailor's delight." Farmers observed that dandelions and other flowers closed when a storm was approaching and had a simple way of telling the temperature from the rate at which crickets chirp: count the number of times the insect chirps in 14 seconds and then add 40.

Meeting of Masses. But contemporary weathermen base their forecasts on ever-evolving knowledge about how the world's weather machine works. They know that cool air generally brings dry weather and clear skies and that warm air ushers in clouds. They have also learned what happens when air masses of different temperatures meet. A warm, moist air mass, being lighter, tends to ride up and over a cold mass, bringing long, warm rains. A moving mass of cold air, being heavier, tends to plow into a warm air mass like the blade of a bulldozer, triggering brief, violent precipitation at the front, or leading edge, and leaving clear skies in its wake.

Weather forecasting has improved in recent decades. Satellites now track storms from high above the earth. Monitoring stations provide agencies such as the National Weather Service with thousands of readings daily, recording air and sea-surface temperatures, barometric pressures, relative humidity and wind velocities and directions. Sophisticated computers enable weathermen to perform in minutes calculations that might otherwise take months.

With all these aids, short-term forecasting is relatively reliable. For example, a meteorologist can see that a mass of cold, dry air is moving down from Canada at 960 kilometers (600 miles) a day. He can check its direction, figure out how long it will take for its front to collide with, say, a warm, moist air mass sitting over New York and tell about when and where the resulting rains will begin (see chart). Weathermen can make three-day forecasts with reasonable accuracy.

Gambler's Hunch. But beyond three days, the meteorologist's batting average falls rapidly. Five-day forecasts are considerably less accurate; a 30-day forecast is usually little better than a gambler's hunch. "It's like playing dice," says Warren Washington of the National Center for Atmospheric Research in Boulder, Colo. "The odds are that a 30-day forecast will be better than a purely random guess--but not much better." Still, both Jerome Namias of California's Scripps Institution of Oceanography and Donald Oilman, director of the National Weather Service's Long Range Prediction Group, using advanced theories and masses of data, last fall accurately forecast this winter's weird weather patterns. The U.S. Weather Service's 30-day forecast for the period ending January 15, however, was only partially correct. The Service accurately predicted below-normal temperatures for New England and upstate New York, but incorrectly foresaw near-normal temperatures for the New York City area and much of the South and Midwest. It predicted below-normal precipitation for most of the northern half of the country--not the snows that paralyzed Buffalo.

Weathermen acknowledge that there are still enormous gaps in the meteorological data that they need for more precise predictions. There are huge areas of the Southern Hemisphere, for example, for which no sea-surface temperature, wind direction and velocity or barometric pressure readings are available.

More work must also be done on developing computer models of the weather. But no matter how advanced the tools and theories, most meteorologists concede that certain aspects of atmospheric behavior simply cannot be predicted.

Yet some of that behavior may be modified. Early man tried to influence the weather by using a variety of techniques, including sacrificing virgins or staging rain dances. Renaissance Europeans, noting that rains seemed to follow battles, theorized that the waters were shaken loose from the clouds by the noise of cannon.

Most historians date scientific rainmaking from 1946, when General Electric Researcher Vincent Schaefer put frozen carbon dioxide, dry ice, into a freezer and watched as a miniature cloud formed and snowflakes began falling. Several months later, working with Irving Langmuir, he tried his experiment on a larger scale. From a plane, he dropped dry ice into a cloud. The ice pellets triggered the formation of ice crystals, which melted into rain as they descended through the warmer layers of the atmosphere. Today, cloud seeding with dry ice or with silver iodide (which provides nuclei for the formation of ice crystals) is frequently carried out by Government and private rainmakers. The process has been used with some success to trigger rains over drought-parched Western and Midwest farm land. Cloud seeding has also been used in attempts to disarm hurricanes. In 1969 scientists seeded the clouds in the wall of the eye, or inner ring, of Hurricane Debbie; the wall expanded upward and outward, and its wind speeds decreased.

In another attempt to influence the weather, the U.S. Department of Defense spent $21.6 million on a seven-year program of cloud seeding to induce rain over parts of Southeast Asia during the Viet Nam War. Major purpose: to turn the Ho Chi Minh Trail, by which the North Vietnamese forces were being supplied, into an impassable quagmire. Its success: questionable; data produced by military authorities are insufficient to support their claim that they caused as much as 18 centimeters (7 in.) of rain to fall in one area during June 1971. The Soviets seem to have had better luck in their efforts to control hail by seeding clouds using rockets and artillery shells. In one region near the Bulgarian border, hail damage to crops was nine times greater in an unseeded area than it was in a section where clouds were seeded by Oblako rockets.

Even more elaborate weather-modification ideas have been proposed. Krafft Ehricke, a German-born rocket engineer, has revived an earlier suggestion that huge orbiting mirrors be used to reflect sunlight onto the dark side of the earth, preventing crop freezes and perhaps raising average temperatures enough to forestall the new ice age that some climatologists believe lies ahead (TIME, Jan. 31). Others have suggested paving large areas of desert with blacktop, which would absorb the sun's heat and warm the air above them, causing strong updrafts that could draw moist air in from nearby oceans.

Some scientists would like to see weather-modification programs accelerated. The U.S. Bureau of Reclamation, Colorado State University and others have conducted studies showing that carefully designed cloud-seeding programs can increase snowfall in areas of the Rockies by 15% or more, and Colorado authorities have appropriated nearly $200,000 for seeding clouds in four areas of their state. Lewis Grant of Colorado State University believes that clouds over the Rockies should be seeded routinely in years of abnormally low snowfall. Says he: "As far as I'm concerned, the medicine has been on the shelf ready to use for five years."

Safety Valve. But weather modification could also prove to be a mixed blessing. Ray Davis, a University of Arizona law professor, says rainmaking could be considered a form of "cloud rustling" and believes that diverting another nation's or state's cloud system could be construed as illegal diversion of its water. Says Davis, "If one country causes environmental harm to another, there is liability." He also cautions that weather modification could become a form of warfare, enabling hostile countries to cause droughts or floods in the lands of their enemies.

The long-term effects of weather modification might be even more disastrous. Meteorologists point out that tropical storms serve as an environmental safety valve, enabling the planet to distribute the enormous heat that would otherwise build up around the equator. Preventing these storms, they warn, could drastically alter the earth's atmosphere and climate, possibly for the worse. Others fear that altering weather patterns over one region of the globe could result in the disruption of rainfall and damage or even destroy vital crops elsewhere.

The more that scientists learn about the world weather machine, the more they realize that it is an engine of enormous complexity. They are only beginning to figure out how it works or predict what it will do next. Until man has a better understanding of the weather, he is wise not to tamper with it.

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