by John Cairns,University Distinguished Professor Emeritus of Biology

Are the causes of environmental problems scientifically proven?

When concerned people talk about global warming and acid rain, they sometimes are countered with the statement, "It is not a scientifically proven fact!" as if that means we don't have to be concerned.

Unfortunately, what it means is we don't have a good understanding of what science means. Many people do not understand how science really works.

Science works by disproving things. There is rarely absolute proof or certainty. Most 'facts' are merely highly probably, not absolutely certain.

The news media sometimes use the word ‘theory' to imply that there is great uncertainty about whether the mix of gases in the atmosphere is a major determinant of the earth's temperature. However, there is not major scientific debate about that question.

Scientists working on atmospheric problems have recognized for nearly a century that water vapor, carbon dioxide, methane, and other gases trap radiation, including heat. They have concluded, for example, that Venus is hotter than earth because its atmosphere is made up almost entirely of carbon dioxide.

What scientists are debating is the extent to which changes in the gaseous mixture around the globe will change the earth's temperature.

The greenhouse theory (that increased carbon dioxide and other gases in the atmosphere can trap heat near the earth) is well accepted by mainstream science worldwide. Furthermore, a clear relationship has been detected between global temperatures and concentrations of carbon dioxide and methane in the earth's atmosphere in prehistoric times. This was done by examining air bubbles in the Antarctic ice cap. The core contains samples of air spanning two 'ice ages' and two warm interglacial periods. During this period, the average global temperature changed over a range of about 10 degrees and concentrations of carbon dioxide and methane changed along with it. Thus, certain changes in the atmosphere were associated with certain changes in the earth's temperature.

Nevertheless, it does not constitute conclusive evidence that changing the atmosphere either did or will inevitably change the temperature. For example, a baseball player's batting average could closely follow the stock market's ups and downs. It is doubtful that the batter is affected by the stock market. On the other hand, if there is increased drug use by pregnant women and the number of birth defects increases simultaneously, it would be prudent to see whether there is a connection between the two events.

It is well to remember that people often resist new discoveries in science because they seem intuitively unreasonable. For example, Copernicus, one of the world's great astronomers, showed in the early 1500's that the earth is not the center of the universe and that the earth revolves around the sun, not the sun around the earth. Copernicus was ridiculed, as have been many other now-revered scientists. Some even suffered physical harm for stating their beliefs.

Almost all new ideas carry with them a high degree of uncertainty. But when the consequences of the changes projected may be catastrophic, it is a good idea to look at the evidence in detail and objectively, rather than responding emotionally. Just because we don't wish to believe that something is true does not ensure that it will not happen.

Nor do we have to wait until a concern is a ‘scientifically proven fact’ to take action.

(John Cairns is a nationally recognized expert on the environment. He is a member of the National Academy of Sciences and official adviser to the federal government on questions of science and technology. He has been honored for his work by the UN and EPA, and received the Life Achievement Award from the Science Museum of Virginia. He does research to improve the quality of information used in making environmental decisions.)