by Whit Gibbons

November 25, 2002

Predictions can drive our actions, depending on their reliability and their consequences. Thus, although presumably reliable, a prediction by astronomers that two black holes will collide in space a distance of 400 million light years from Earth should not determine what you buy at the grocery store next week. On the other hand, an ice storm next week could significantly affect your plans. But the past record of local weather predictions in most regions is so dismal who would put together Saturday's shopping list based on Monday's ten o'clock weather report?

So how should we respond to predictions of changes in climate, the average long?term weather conditions in a region that could potentially have major consequences on our lives? I think we should heed the warnings promulgated by eminent scientists.

One practical reason for developing predictive models of Earth's changes hinges on concern for such phenomena as global warming and depletion of the ozone layer. For example, according to reputable sources, concentrations of gases in the atmosphere, namely chlorofluorocarbons (CFCs), the coolants used in air conditioning, have increased measurably since the 1950s. Continued overuse was predicted to cause further destruction of the ozone layer.

Likewise, dire predictions of global warming from some scientists have been based on measurements of increases in carbon dioxide and methane, "greenhouse gases," that end up as a shroud around the earth. Whether governments pay attention to and take action based on these predictions could determine how livable the world will be in the future.

Scientists trying to predict climate base their calculations on past climatic conditions. Several techniques have been developed to establish associations between cosmic conditions and the earth's atmospheric state. In addition, relationships have been established between global conditions and the presence of glaciers, the temperatures of tropical seas, and the advent of humans. One technique measures trace gases that were in the atmosphere up to 150,000 years ago by examining deep layers of polar ice formed centuries ago. The age of the ice layers is estimated based on known rates of deposition. Using complex procedures, scientists can measure gas levels in air bubbles trapped in polar ice. The trapped air presumably represents a sample from earlier times in Earth's history.

According to some findings using this technique, carbon dioxide and methane have increased steadily since 1750, roughly the beginning of the Industrial Revolution when power?driven machinery and factories began to be common. Thus the abrupt rise in levels of carbon dioxide and methane is attributed to humans and, as stated in one report, "support the prediction of a significant greenhouse warming [effect] for the next century."

Another method for gauging past climates and therefore more effectively predicting future ones is to relate periods of high and low temperatures to cosmic and geologic patterns. The earth's climatic history has presumably been greatly influenced by variations in the earth's orbit and orientation toward the sun that appear cyclical. The earth today is closest to the sun in January (winter in the Northern Hemisphere because of the tilt of the axis) and farthest away in June. But studies of celestial movement patterns indicate that 11,000 years ago the opposite was true, the consequence being colder winters and hotter summers. Can subtle celestial changes be predicted for the not?too?distant future that might result in more than subtle climatic effects?

The world's climates are not static. Glaciers once covered what is now the upper portion of the United States. Oceans once covered land where forests and cities now thrive. Even the world's carbon dioxide levels have been both higher and lower than today, although uncertainty exists about the true amounts.

According to some estimates, carbon dioxide levels 400 million years ago were as much as ten times higher than those today. So why worry about global warming? Well, consider this? Has the earth ever before experienced such abrupt and rapid increases in carbon dioxide? If so, then dramatic fluctuations may be within the realm of natural responses. If not, we should perhaps be a bit concerned.

If climates begin to change in our lifetimes, we will have worries of a different magnitude. Maybe we should forget about weather reports we cannot affect and pay more attention to climate forecasts that we can.

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