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The inevitability--and limits--of dissent


IN 1965 IT WOULD have been difficult to find climate scientists who believed that humanly caused greenhouse warming was in progress, and for good reason: Average global temperatures had been declining since about 1940. That decline had ended by 1980 when scientists who prepared the Global 2000 Report, commissioned by President Jimmy Carter to survey the world's environmental problems, regarded scenarios of global warming to be as likely as global cooling. By the late 1980s, amid record high global temperature measurements, hardly anyone doubted that a general warming was occurring, though it could easily have been of natural origin.

According to William Stevens, writing in the New York Times of Sept. 10, 1995, climate experts on the Intergovernmental Panel on Climate Change (a United Nations body commissioned to advise the world's governments) agreed for the first time in 1995 that human activity is a likely cause of the warming of Earth's atmosphere. Thus, over the past three decades there has been clear movement of scientific opinion in the direction of a consensus for humanly caused greenhouse heating.

The consensus is not complete and never will be. Complete agreement within the scientific community is like the end of the rainbow: You may approach it but never reach it. There are bona fide scientists today who insist that the fluoridation of drinking water is a major cause of cancer, that cold fusion is a real phenomenon, that AIDS is not caused by HIV infection, that aliens have visited Earth, or that Noah's flood was a historic worldwide catastrophe. Science is not like a slot machine, where in one sublime moment three cherries come up and everyone knows that's a winner. Scientists have all the human foibles that create dissenters, including stubbornness, envy, defensiveness, and simple variation in what kind of evidence one requires to become convinced of something.

When scientists do achieve a near consensus, it does not mean that their position is correct, but only that it is their best collective effort. Consider the handful of climate modelers in the United States and elsewhere who use complex supercomputer programs to simulate past climate records and project future warming scenarios. These groups are competitive to a degree, each seeking their share--or more--of scarce funding and professional esteem, by doing better work than the other groups. But they are also cooperative, ensuring that one computer projection is not wildly out of line with the others, since all groups benefit from public faith in their efforts, and each would lose if funders came to regard modeling projections as chaotic and unreliable, with no more validity than long-term weather predictions. Each group follows the work of the others. Therefore, it is not surprising that their various published estimates of global temperature increase due to a doubling of atmospheric CO2, compiled in 1993 by M. den Elzen (1), were less diverse (and lower in magnitude) in recent years than in their early runs.

Does this mean that the modelers are finally getting it right? Not necessarily. Computer models of this kind are notoriously flexible and can be tuned to produce desired patterns of output. If global temperature were to drop steadily over the next decade, no doubt the various modeling groups could incorporate a suitable mechanism into their simulations to replicate that decline. So a consensus of modeling projections might not convince many of us that agreement means accuracy. On the other hand, it would convince me that these projections are the best that these modelers, collectively, are going to come up with.

If it is true that sophisticated observers once regarded science as wholly objective, surely that is no longer the case. Today it is commonplace to see scientists who represent opposing interest groups make contradictory factual claims to bolster their respective sides. We recognize that the products of science, like all human productions, are to some extent arbitrary social constructs reflecting personal, structural, and historical influences. Indeed, there are some sociologists of science who insist that science is not fundamentally different from any other method of knowing; from this position it follows that scientific claims have no special status as statements of truth. Probably more numerous are those, including most scientists themselves, who believe that the process of modern science, despite its subjective elements, does eventually discover real features of nature (viruses, ions, gravitational attraction, electromagnetic radiation, supernovae) in a way that other methods of knowing cannot, and that the special quality of this knowledge is manifest in the power of modern technologies that are based on scientific theory.

For those of us who hold this realist view, "objectivity" and "subjectivity" are taken as relative-not absolute-terms, and scientific knowledge is considered more objective than other systems of belief about the natural world; thus, it deserves special status. We regard the novel claims of an individual scientist as less objective than claims that appear in standard textbooks or are accepted by most informed scientists, though we expect that these novel claimants will occasionally be correct (but usually not). Furthermore, we distinguish established scientific knowledge, wherein scientific claims are trustworthy, from areas of active research where knowledge is uncertain. Most highly subjective, contradictory, or incorrect scientific claims occur in the areas of uncertain knowledge, or in the application of well-established knowledge to a novel or ambiguous situation (as when the established "greenhouse mechanism" is applied to atmospheric warming). Finally, we assume that the body of established scientific knowledge is cumulative and growing rapidly, and that many controversies over competing scientific claims are eventually settled in a reasonably objective manner.

In my own view, the power of science lies in three advantages. First, scientists tend to be intelligent, which is a necessary though not sufficient condition for intellectual achievement. Second, scientific reasoning is rational, meaning that theories must be consistent, logical, and mathematically correct, which is a clear improvement over other forms of reasoning still current. Finally, the requirement of modern science that theory be consistent with observation, for all its flexibility in application, is a unique constraint on speculation and has an excellent track record of discovery. None of these features guarantees good science, but they help greatly. The bottom line of all this is that our best reading of scientific truth is what the consensus of scientists believes it to be-maybe not God's Truth, but as good as we are going to get. If climate scientists eventually reach a strong consensus that humans are causing global warming, we ought to believe it.

However, even if God spoke to us, affirming that humans are warming the atmosphere, this would not dictate a change in our ways. Policy decisions require value judgments; they do not follow from facts alone. Americans and Europeans might plausibly argue that any reduction in our use of fossil fuels would be pointless because it would be swamped by China's massive increase in coal burning during the next century. Or we might simply prefer to let the next generation watch out for itself. These are value choices, independent of facts.

  1. Elzen, M.G.J. den. Global Environmental Change--An Integrated Modelling Approach (Utrecht, The Netherlands, International Books, 1993.

ALLAN MAZUR is professor of public affairs, Center for Environmental Policy and Administration/Center for Technology and Information Policy, Maxwell School of Citizenship and Public Affairs, Syracuse University. A specialist in the social aspects of technology, he is the author of The Dynamics of Technical Controversy (Washington, D.C.: Communications Press, 1981) and Global Social Problems (Englewood Cliffs, N.J.: Prentice-Hall, 1991).

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