The biggest concern facing Earth scientists today is the question of what people are doing to the planet. Our influence is massive. We undoubtedly affect climate and weather. But we don't know what we're doing. And until we find out, it's foolish to scare ourselves with scientifically questionable forecasts of doom. Yet, because some scientists continue to use the politics of fear to influence public policy, it's worth taking a quick look at recent developments concerning three of the popular scenarios.
The issues are serious. The need for research is great. But the fear has more in common with the Chicken Little fable than with science.
Nuclear winter. The thesis that smoke from fires ignited by nuclear blasts would cause a life-extinguishing chill has scared a lot of people.
Now the scientific uncertainties -- which everyone acknowledged -- have undermined this fearful notion. Stephen H. Schneider and Stanley L. Thompson of the National Center for Atmospheric Research (NCAR) have run the most refined computer simulations of nuclear winter yet made. The original uncertainties include such factors as the effects of the oceans in moderating the chill. Taking such effects into account, Schneider and Thompson find that the the nuclear cold would be short-lived and more like autumn than winter.
They do not say that the smoke would have no climatic effect. Indeed, they urge continued research to refine the prospects. But, as they explain in the summer issue of Foreign Affairs, ``There does not seem to be a real potential for human extinction; nor is there a plausible threshold for severe environmental effects.'' That threshold would be the minimum intensity of nuclear explosions needed to trigger nuclear winter. Some arms control advocates had argued for reducing nuclear arsenals below such a threshold, crudely set at between 500 to 2,000 warheads.
``Thus,'' the NCAR scientists say, ``the two unique conclusions of the original nuclear winter idea with the most important implications for policy have been removed.'' They warn against basing arms control policy on such uncertain science as that involved with nuclear winter.
The ozone scare. Stratospheric ozone filters out harmful ultraviolet radiation from sunlight. Its loss would be catastrophic. Scientists worry that fluorocarbons used in refrigerators and air conditioners leak into the stratosphere and destroy ozone.
Computer studies are inconclusive. Yet alarmists urge action to curb use of the chemicals now. They seize on every indication of ozone loss, however ambiguous, to bolster their case. Currently, they cite a drop in ozone over the Antarctic.
NCAR's Francis P. Bretherton, chairman of NASA's Earth System Sciences Committee, led a study of the research needed to understand humanity's environmental impact. Asked about the ozone hole, he explained that, scientifically, it represents ignorance. It may be just a natural fluctuation. We need to know what's happening. But there's no basis for hand-wringing.
Melting ice caps. The carbon dioxide from burning fossil fuels and other heat-trapping gases such as methane from rice paddies are slowly accumulating in the atmosphere. They may indeed warm the climate a bit over the next century. But no one knows how great the warming will be or what its consequences may entail.
Here again, there's more need for research than panic. For example, the influence of clouds in moderating the warming is one of the big uncertainties. Earlier this month, NASA reported a study suggesting that cloudiness might adjust itself to offset the so-called ``greenhouse'' warming. Data from the Earth Radiation Budget Experiment satellite indicate that clouds reflect more heat back into space than they retain. They appear to cool Earth's climate. No one yet knows how this fits into the overall greenhouse story. But our lack of understanding of such factors shows that our ignorance is still too great to support any climatic alarm.
Scientists who use fear to influence policy try to bring public awakening through imagined destruction. They lose credibility when they use shaky science. Because this obscures the legitimate need for research, they do disservice to both science and the public.
Robert C. Cowen is the Monitor's natural science editor.