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Ozone depletion
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  Evidence at last
One of the benefits of a large, diverse scientific community is that many scientists can simultaneously work on the same problem from different angles. Some scientists worked in labs refining the sub-hypotheses contained within the models and the Molina-Rowland hypothesis. Some worked on developing more sophisticated models that could more accurately determine the expected results. And others worked on getting atmospheric measurements to test the hypothesis.

Ozone concentration fluctuations between 1926 and 1975

Ozone levels fluctuate so widely that it is difficult to detect subtle trends over a short-term period, as shown by these ozone measurements for the atmosphere over Switzerland taken between 1926 and 1975.
The ultimate test of the Molina-Rowland hypothesis would be finding actual ozone depletion, but in 1975, that evidence was not easy to come by. First of all, according to the models, it would take a long time for CFCs to move high enough in the atmosphere to be broken down — and that means that we should expect a delay between when CFCs are released and when the ozone layer is damaged. Secondly, ozone levels fluctuate naturally — up to 10% given the season, time of day, and the sun's energy output — and all this variation makes it more difficult to detect subtle changes in average ozone level. The Molina-Rowland hypothesis predicted that, even with the delayed reaction, some ozone depletion would have occurred by 1975, but it would have been impossible to separate from all the natural fluctuations in ozone levels.

Instead, scientists turned to a different expectation generated by the models: the levels of CFCs that ought to be found at different altitudes. According to the models, CFCs should be completely unaffected in the lower atmosphere but destroyed by solar radiation at higher altitudes. In 1975, using high-flying aircraft- and balloon-borne instruments, two independent groups of scientists measured CFC concentrations at different altitudes. Their results confirmed that CFCs reached the upper atmosphere in amounts consistent with the idea that CFCs are unscathed by their journey through the lower atmosphere. The results also showed that, as CFCs moved through the upper atmosphere, they were being destroyed at the rates predicted by the Molina-Rowland hypothesis.

The Molina-Rowland Hypothesis

Despite this evidence, some weren't convinced that a ban on CFCs was the right action. Given the large economic impact of a ban — it was estimated that industries relying on CFC production generated $8 billion in business and employed 200,000 people in 1974 — several scientists in the field advocated waiting a few years for science to make more progress on the issue before making any policy decisions. They didn't doubt the scientific validity of the hypothesis, just the wisdom of a ban. CFC manufacturers, on the other hand, were trying to cast doubt on the Molina-Rowland hypothesis any way they could. Industry spokespeople repeatedly downplayed the idea as "just a hypothesis," neglecting to mention the evidence supporting it. The industry also brought out their own "expert" to challenge Molina and Rowland's ideas, sponsoring a month-long speaking tour for Richard Scorer — a professor well known for his research on pollution, a lower atmosphere phenomenon. Despite all the hype from the CFC industry, the facts that Scorer had not published a single scientific paper on the chemistry of the upper atmosphere or conducted any research within the field made him an untrustworthy source of information on the Molina-Rowland hypothesis.

take a sidetrip
  • Many different scientists worked on the CFC problem from many different angles. For more information on the role of community in science, see Science: A community enterprise.

  • Some aspects of the CFC debate were clouded by media messages. For more information on how to find trustworthy sources of information and separate science from spin see Untangling media messages and public policies.

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