We have already admitted that we do not know the cause of the large-scale glaciations that have taken place at various times in the earth’s history. In one sense, investigating the cause is an academic exercise; on the other hand, some hypotheses describe changes in the atmosphere which may relate to modern atmospheric changes being made by man. There are literally dozens of hypotheses for the cause of the ice age. Many of them have serious flaws, many rely on unique happenings on the earth or in the solar system and many require special physical or chemical conditions. As yet, we lack the knowledge to prove any hypothesis.
The various theories can be grouped into (1) astronomical and (2) terrestrial hypotheses. The first group includes those which involve changes in the relationship of the earth to the sun or other bodies. For example, it has been variously suggested that glaciation has been brought about by (1) a decrease in radiation given off by the sun, (2) an increase in distance between the earth and the sun resulting in colder temperatures on earth, and (3) a decrease in the tilt of the earth’s axis, causing a decrease in the sun’s energy received at higher latitudes in the winter. It has also been suggested that the earth, traveling through the galaxy with the rest of the solar system, has passed through concentrations of dust. The dust would provide extra nuclei around which drops of precipitation (snow) could form.
The second group of hypotheses include those which refer to changes taking place as a result of processes occurring on earth. These involve possible changes in land masses, in the oceans, in the atmosphere, or in combinations of these. For example, a time of increased volcanism might have added dust to the air which served as condensation nuclei. Uplift of a land mass could have diverted or blocked oceanic currents, thereby changing the climate, especially if polar areas were affected. Conversely, the submergence or splitting of a land mass could have changed the oceanic circulation. It has been suggested that polar wandering and continental drift operated in such a way that the continents and Arctic Ocean were placed in precisely the right positions for the intricate mechanisms of evaporation, condensation, and precipitation to cooperate in a sequence which produced an icecap over places now far removed from the poles.
Hypotheses which indicate the atmosphere as the cause of glaciation mostly involve changes in the amount of carbon dioxide (CO2), water vapor, or dust present. Because CO2 absorbs long heat waves given off by the earth, an increase in atmospheric CO2 might cause a warming of the earth’s surface. Increased evaporation might then occur, adding moisture to the air which, in high latitudes, would fall as snow. On the other hand, the increased moisture content could produce an increased cloud cover, and clouds could cause the solar energy to be reflected back into the space. Eventually, therefore, the earth might cool due to the lack of solar energy, and because melting of the snow would be slowed, a glacial age would ensue.
As yet, the available data are insufficient to allow predictions based on a change of the variables of the system to be made. This explains the reasons for the debate about the consequences of moisture which would be added to the atmosphere by a supersonic air transport plane (SST). We are at least aware of the fact that the lithosphere, hydrosphere, and atmosphere comprise a highly complex system that includes a great number of physical and chemical variables. Taking the time dimension into account, we should clearly realize that the reason it is so difficult to understand the causes of the Ice Age is that we are far removed from the time in which these events occurred.
Why dwell on this? This becomes understandable if one considers the following: first, the earth is dynamic, not static. Who is to say that we have seen the last of the ice ages, when we do not even know what caused them? Was the Wisconsin stage the last, or will there also be a Minnesotan or a Kentuckian stage? Second, the onset of the stages of the Pliestocene occurred rapidly in geological terms, as well as in terms of human history. Civilization could be affected drastically if another glacial stage were to occur. Third, if adding carbon dioxide to the atmosphere is indeed a cause of glaciation, we might be capable of bringing about another ice age.
We know that since the beginning of the industrial age we have added roughly another 10 percent to the carbon dioxide content of the atmosphere. This has been entirely a result of the burning of fossil fuels. If you note . . . that we have, so far, burned less than one-tenth of the world’s coal and petroleum, it should be obvious that the continued burning of fossil fuels will contribute an enormous amount of carbon dioxide to our atmosphere. Whether or not the oceans will be able to take enough carbon dioxide from the air and store it in solution, thus the balancing situation, is unknown.
What might happen if the ice in Greenland and Antarctica should melt or even begin to increase? If all the ice in the icecaps were to melt, enough water would be added to the ocean to raise the sea level about 200 feet. Consider the results: coastal areas would be inundated, places such as Holland and Florida would be almost entirely under water, and all of the world’s seaports would have to be abandoned. In the United States, many of the major cities would be included: New York, Boston, Philadelphia, Baltimore, Washington, Miami, New Orleans, Los Angeles, San Francisco, San Diego, Seattle, and hundreds of others would be completely, or almost completely, under water. Rich and important agricultural lands would disappear, and hordes of the world’s populace would jam onto the shrunken continents. The ecology of fisheries and wildlife habitats would alter radically as the coastline configurations were changed.
On the other hand, what if the the icecaps grew and another glacial age occurred? Since water would then be withdrawn from the oceans and incorporated into icecaps, the sea level would be lowered. By mapping features that form above the water and which are now submerged, we know that the sea level was as much as 300 feet lower during the Pliestocene glacial stages than it is today. Large areas of the continental shelves--those portions of the continents which lie under the sea--were exposed at that time. Were this lowering of sea level to occur again, our seaports would be located on dry land, the plant and animal ecology would be greatly changed, and more land would be available for living space or other use. Whether this land would be suitable for agriculture is another problem, as conditions might be too cold or too dry to permit cultivation of the land.
In either case, the climate would change because of factors that induce such an advance or retreat. In addition, local climatic changes would occur here and there because of changes and land geography and the shifting of ocean currents. All of these changes would involve temperature and precipitation changes, with concomitant changes in water supply, wildlife, agriculture, and our life-style.