More cracks appear in `nuclear winter' predictions

Nuclear winter continues to melt. The more scientists refine their computer studies, the more it appears that an Ice Age chill is not an inevitable consequence of nuclear war. Now an analysis of such studies by Joyce E. Penner of the Lawrence Livermore National Laboratory shows the scientific uncertainties to be so large no one knows what the climatic consequences of nuclear war might be.

It's important to clear up those uncertainties to the fullest extent possible. Few climatologists doubt that the smoke and dust thrown into the atmosphere by nuclear war could affect climate. Arms control strategists need to know what to expect. But, as Penner explains in the Nov. 20 issue of Nature, nobody knows that yet.

Meanwhile, what has become clear is the shoddy nature of the manipulative public-relations campaign that hyped half-baked science as a prophecy of climatic disaster. Russell Seitz, a visiting scholar at the Harvard Center for International Affairs, details this story in the fall issue of the journal the National Interest.

Even before the original - admittedly simplistic - study had been through the review process that normally precedes scientific publication, nuclear winter's promoters hired an advertising agency to get their message across. As Seitz notes, ``More money was spent in the 1984 fiscal year on video and advertising than on doing science.''

It's important to realize why the science involved is half-baked.

Penner lists several major uncertainties. There's the simple fact that no one knows how much smoke or what kind of smoke might be involved. She notes that the published range of values assumed for the smoke emission factors ``may not even include the right value.''

Clouds are expected to form over large fires. No one knows how effectively these would scavenge smoke particles and rain them out. Lack of good data on the optical properties of the smoke make it hard to estimate how thoroughly it would block sunlight. Penner finds that ``published estimates [of those properties] yield a wide range of values, which allows the prediction of either comparatively minor effects on climate or massive effects.''

Penner concludes, ``It seems clear, therefore, that nuclear winter is not necessarily a probable outcome of nuclear war, although it's certainly a possibility.'' Much more research is needed to predict effects on climate. That includes experiments with large fires to get good data on the smoke - experiments such as those now planned by the United States Defense Nuclear Agency.

The original nuclear winter prediction was also based on poor computer simulations. These neglected such basic elements as the difference beween land and sea. In recent, more sophisticated simulations, the predicted cooling has lessened. Some of the latest computer runs foresee only mild temperature drops, although these could include summer frosts in middle latitudes.

As an attempt to understand what nuclear war might do to climate, this is good research as far as it goes. But it has yet to yield such understanding. That's why it can only provide half-baked scientific support for propaganda that uses fear of nuclear winter to try to influence arms control strategists to reject nuclear weapons.

As climatic modeler Stephen H. Schneider of the National Center for Atmospheric Research points out, nuclear winter remains ``a scientific and socially important problem, even if `global G"otterd"ammerung' is not a likely outcome.'' Schneider, whose own research has tempered nuclear winter's chill, explains in a letter in the Wall Street Journal: ``...the process of science is to step from simple ideas to more complex calculations. That is what has happened in the nuclear winter case, a normal evolution of science.''

Schneider also regrets that press and public lose sight of the scientific context of this research, ``focusing instead on the latest up or down calculation.'' That could be avoided if all scientists followed Schneider's lead and let this research go through a normal evolution. But it's hard for lay press and public to share Schneider's perspectve when some scientists launch a media blitz.

What's at stake here is sound arms control policy and scientific credibility. We need less fear and more knowledge to make better policy. And as Joyce Penner told the Associated Press: ``If any of this [nuclear winter research] is going to have any effect on nations, it has to be credible. As long as these scientific uncertainties are floating around, it's not as credible as it can be.''