Man's Inadvertent Modification of Weather and Climate

M

AN MAY be changing his weather. And if he is, the day may come when he will either freeze by his own hand or drown. The delicate balances within the atmosphere and the history of climatic change in the past suggest that through his inadvertent actions he may be driving the atmosphere either to a disastrous ice age—or as bad-to a catastrophic melting of the ice caps. Either may literally be possible, but it depends on just what he is doing to the atmosphere. He does not know for sure.

Evidence continues to build that his activities and his growing populations alter the chemical composition of the earth's atmosphere and change its heat balance. And in turn these two alterations, in tandem, change weather and climate. But the processes and outcomes of such changes are largely unknown.

The science and technology of weather modification are only in their infancies. But they could grow overnight if man will increase his efforts to learn what he is inadvertently doing to his own atmosphere.

CLIMATIC CHANGES OF THE PAST

Geological and historical records clearly show that major climatic fluctuations have taken place down through history. Since the last advance of the ice sheet in Eurasia about 10,000 years ago, the permanent ice cover in the Northern Hemisphere has been limited largely to the Arctic Ocean, Greenland, and some high latitude islands.

But alternating periods of warming and cooling have occurred during the last 10,000 years. In the last century, instruments have been available to keep current records, and they show a pattern of climatic fluctuations.

Climate is much too complicated to be described by any single parameter. One useful guide is the average annual temperature at the earth's surface. Beginning in about 1890, this average temperature began an irregular climb. By 1940, it was 1.1° F. higher than it had been during the decade from 1880 to 1890. But in the 30 years from 1940 to 1970, the average temperature has fallen about 0.5° F. Thus, during the last three decades, one-half of the warming that occurred during the preceding six decades has been erased.

Associated with rising temperature in the Northern Hemisphere were movements of the frost and ice boundaries. Simultaneously, pronounced aridity gripped the south central parts of Eurasia and North America. This led to dust-bowl conditions in some areas and a northward displacement of the polar fronts. The recent lowering of the temperature has been accompanied by the shifting of frost and ice boundaries to the south and marked increases in rainfall in parts of previously arid continental regions. In the last two winters, ice coverage in the North Atlantic has been among the most extensive in over 60 years. Because of it, Icelandic fishermen suffered great losses, and the colder temperatures substantially diminished Iceland's agricultural output. In contrast, the rains in central continental regions, particularly in India and East Africa, contributed to high wheat yields. These experiences illustrate dramatically how sensitive the complex pattern of human activity is to relatively small shifts in climate. Man's ability to predict such changes is still very limited.

These fluctuations of only a few tenths of a degree observed over decades are small compared to the climatic variations of the "Little Ice Age” from 1650 to 1840, the warmer period between A.D. 800 and A.D. 1000, and the still larger variations of a few degrees associated with the few earlier ice ages and their retreats.

HOW MAN CAN CHANGE CLIMATE

The key question is: To what extent are climatic fluctuations of the past years due to natural processes or to man's intervention?

Man can change the average atmospheric temperature slightly and thus significantly affect climate in at least seven ways:

• He can increase the carbon dioxide content of the atmosphere by burning fossil fuels.

• He can decrease atmospheric transparency with aerosols (tiny solid or liquid particles floating in the air) from industry, automobiles, and home heating units.

• He can decrease atmospheric transparency by introducing dust (particles larger than aerosols), primarily through improper agricultural practices.

• He can alter the thermal properties of the stratosphere (upper atmosphere) with water from the combustion of jet fuels.

• He can heat the atmosphere by burning fossil and nuclear fuels. • He can change the ability of the earth's surface to reflect sun radiation back into space through urbanization, agriculture, deforestation, and reservoirs.

• He can alter the rate of transfer of thermal energy and momentum between the oceans and atmosphere by spilling oil on the water's surface. Such oil films on the ocean come from incomplete combustion or spills from sources such as vessels and drilling towers.

Carbon Dioxide-An Earth Warmer?

The atmosphere's energy, which determines weather and climate, is derived primarily from visible solar radiation absorbed by the earth's surface and atmosphere. The absorption of that energy tends to raise the temperature at the surface. The earth's surface maintains its thermal balance (keeps from overheating) by radiating energy back to space at longer wavelengths. Carbon dioxide in the atmosphere absorbs incoming visible radiation, but in amounts too small to have any appreciable effect on the radiation reaching the lower atmosphere and the earth's surface. However, carbon dioxide is virtually opaque to some long-wave radiation that is emitted by the earth's surface. Thus, when carbon dioxide concentrations increase, heat loss through radiation from the surface is reduced-the "greenhouse" effect.

Attempts have been made to calculate carbon dioxide effects on the average surface temperature. One investigator calculated that atmospheric carbon dioxide content increased at a nearly constant rate from the 19th-century level of about 290 parts per million to 330 in the late 1950's. This increase-about 14 percent-could have caused the temperature rises observed with instruments during the first 40 years of this century.

Recent surprising findings indicate that as increasing fossil fuel consumption raises carbon dioxide output, a lesser percentage of it is retained by the atmosphere, and a larger portion is absorbed by the oceans. Scientists from Sweden and the Environmental Science Services Administration (ESSA) say that only about half the carbon dioxide produced by fossil fuels from 1958 to 1960 remained in the atmosphere. During the last 5 years, less than 40 percent of manmade carbon dioxide has stayed in the atmosphere. Other calculations also show that the effect of carbon dioxide on the temperature, as illustrated in the preceding paragraph, has been overestimated.

A detailed series of observations by Swedish, Scripps Institution of Oceanography, and ESSA scientists shows that from 1958 to 1970 the carbon dioxide concentration in the atmosphere increased from 312 to 320 parts per million—an average annual jump of 0.7 parts per million. This rate, if continued, would double manmade carbon dioxide accumulations in the atmosphere in about 23 years. Yet the bulk of carbon dioxide has entered the atmosphere at a time when the earth's surface temperature was falling rather than rising. Thus, the heating effects of carbon dioxide are apparently being counteracted by natural fluctuations or by other manmade activities.

Any attempt to extrapolate the future effect of carbon dioxide on climate must be uncertain because the fraction of carbon dioxide that will enter the ocean is unknown. If 60 percent of the emissions of carbon dioxide remains in the atmosphere and there is a 5 percent yearly growth of fossil fuel consumption, then by 1990 there would be about 400 parts per million in the atmosphere. If this were not offset by other activity, then the earth's average surface temperature would increase by 1.4° F. On the other hand, if 40 percent of the artificially produced carbon dioxide enters the atmosphere and the present 4 percent growth of fossil fuel consumption continues, then a level of 400 parts per million will not be reached until about the year 2010.