Threat to Ozone Layer Leaves Science Pondering Its Risks

Risky technologies have been making news regularly for at least a quarter of a century, yet each new controversy seems to catch government and the public off guard. The latest example is the discovery of a “hole” in the ozone layer over the Antarctic that is prompting some atmospheric scientists and environmental organizations to call for stronger regulations on ozone-depleting chemicals.

Periodic revelations like this are inevitable, given the complexity of the global ecosystem, the immense variety of technological endeavors and the relative immaturity of the environmental sciences. Yet our public policies too often are framed as if it were possible to achieve a good understanding of all the hazards, real and potential. This leaves many policies unduly vulnerable to surprises. A more realistic approach would assume from the outset that uncertainty is high, and would adopt strategies for mitigating risk that do not rely on the illusory hope of achieving perfect scientific understanding.

The ozone debate illustrates the problem. The Environmental Protection Agency organized a major conference in mid-September to assess scientific knowledge about the Antarctic situation. This was one step in the current strategy aimed at “getting the facts” about the ozone problem. While superficially appealing, this strategy may be fatally flawed, for there are hardly any cases in which science is able to supply definitive answers for risk regulators.

Thus there have been significant revisions in ozone-depletion estimates nearly every year for the past decade. Between 1982 and 1983, for example, depletion estimates were cut in half. In 1984-85, however, new research indicated that ozone destruction might be exponential, potentially leading to depletion more than four times higher than previously believed. Then came the Antarctic puzzle. And there is little reason to believe that the latest revelations will be the last.

What, then, is to be done? The U.S. government’s early decision-making on ozone offers a good model. The 1977-78 ban on most aerosol chlorofluorocarbons (CFC) was enacted even though measurable ozone depletion had not yet occurred. The implicit strategy was to err on the side of caution, rather than chancing ozone depletion while waiting for scientific certainty that might never come. By reducing CFC releases, the ban diminished whatever threat might exist. And it did so at a reasonable cost, since more essential uses of CFC (for refrigeration) were still permitted. Canada and a few other nations joined the ban, but most governments held off in the hope that further research would provide definitive guidance.

Now that pressing new concerns have arisen, is it time to enact additional precautions? Would they be worth the costs--and, if so, how cautious is cautious enough? While these are questions of policy more than science, scientists potentially can provide policy-makers with a basis for sensible judgments about how cautious to be. To achieve this, however, scientific advice needs to be reoriented. Instead of focusing narrowly on the “facts” about atmospheric phenomena, researchers need to focus more on these questions:

--If the ozone situation were deteriorating, how much warning would we get? To the extent that key variables are agreed on, a wait-and-see approach may be satisfactory. The Antarctic confusion may be an indicator of crucial gaps in stratospheric chemistry and physics, in which case a more cautious approach to ozone policy is indicated.

--Is it possible to establish outer limits on the probability and extent of the risks? If consensus is high that the worst conceivable risks are bearable or that severe outcomes are highly unlikely, policy-makers probably can afford to wait. But if scientists cannot set bounds on the risks, policy ought to be erring much further on the side of caution.

--How much depletion could be avoided by what degree of additional restrictions? It might be desirable to reduce the use of numerous chemicals (not just chlorofluorocarbons) that release chlorine, bromine and nitrogen oxides into the stratosphere. But what substitutes are available, how much would it cost to switch to them and what percentage of the total depletion threat could thereby be circumvented? For example, it would be relatively painless to limit the rapidly growing foam-blowing industry, which uses CFC to make molded seat cushions. But would this and other easy options provide meaningful amelioration of the threat? Recent ozone studies have paid little attention to exploring such options. Yet the attractiveness of additional precautions will depend heavily on their economic and political feasibility more than on scientific facts per se .

One small step in this direction occurred at a conference earlier this month in Geneva, where the EPA proposed a worldwide freeze on the production of CFC, and an eventual phase-out. Much stronger measures have been advocated by environmental groups to encourage a search for safer substitutes. But most European representatives were hesitant even about the relatively weak EPA proposal, which suggests that policy-makers still have a long way to go in recognizing the limitations on science as a guide for regulating risks.