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Mending the Ozone Hole: A Triumph of Science and International Policy
by Anne C. Paine


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Compelling science, good monitoring systems, and international cooperation led to success in the effort to eliminate the production of chlorofluorocarbons (CFCs) and stop the depletion of the stratospheric ozone layer, according to Paul O. Wennberg '85, professor of atmospheric chemistry and environmental engineering at the California Institute of Technology.

In a lecture titled "Environmental Science and Policy: Stratospheric Ozone and the Regulation of CFCs," Wennberg, one of this year's MacArthur Foundation "genius" grant recipients, gave an overview of the development and chemistry of CFCs and the movement to eliminate them. His Oct. 5 lecture was part of a symposium celebrating the dedication of the Oberlin College Science Center.

The trouble began with what, at the time, seemed to be a good solution to a vexing problem. In the 1920s, when home refrigeration was beginning, Thomas Midgley, Jr., developed CFCs for use in refrigerants; these gases were safer than the toxic and flammable gases being tested as refrigerants at the time. CFCs eventually came to be used in aerosols, propellants, and foaming agents, and they are still used today in allergy and asthma inhalers.

(Wennberg noted that Midgley's career as a chemist had other unfortunate environmental consequences. Midgley was also responsible for the addition of tetraethyl lead to gasoline as an anti-knocking agent, which significantly increased levels of poisonous lead in the air during the 20th century. This too, at the time, was a good solution to a difficult problem, and no one predicted the adverse consequences that resulted.)

"CFCs are cheap to manufacture, and in the 1980s they were cheaper than milk," Wennberg said. "Eventually they make their way into the atmosphere, which is an oxidizing medium-it breaks down compounds that go into the air. But because CFCs are inert, there's no way for them to be degraded, except at very high temperatures."

Because they are so stable, CFCs move from the lower atmosphere into the stratosphere, where they are eventually broken down by ultraviolet rays from the sun, releasing chlorine. This chlorine is the agent involved in ozone destruction. The ozone layer is essential to life on Earth because it filters out cell-damaging radiation in ultraviolet (UV) light.

By 1974, Sherwood Rowland and Mario Molina predicted from available laboratory data that CFCs release chlorine into the upper atmosphere. They won the 1995 Nobel Prize in chemistry for their work.

"The political response to this scientific speculation varied," Wennberg said. "The United States, Sweden, and Canada immediately banned gratuitous uses-primarily in propellants and foaming agents. But the CFC rates still went up because other countries kept producing them. It was a real problem for U.S. businesses, which were at a disadvantage because they weren't operating on a level playing field. We were trying to solve a global problem on a local level."

By 1985, the U.S. was taking the lead in the international arena, and in March of that year, in Vienna, 21 nations signed on to the Convention for the Protection of the Ozone Layer, which set a framework to discuss and research the ozone problem. The Vienna Convention led in 1987 to the Montreal Protocol, which bound countries to reduce and eventually eliminate CFCs. Supplemental agreements made in London in 1990 and in Copenhagen in 1992 strengthened the protocol.

What was still lacking was concrete, visible proof that the ozone was being depleted. Between international meetings and conventions, Joe Farman, a British Antarctic Survey scientist who had been plotting data for about a decade, provided this evidence when he announced his discovery of the Antarctic ozone hole in a 1985 article in Nature. NASA had also been collecting data that would prove the existence of such a hole, but considering it anomalous, administrators had put the data aside for later evaluation.

"The problem with drinking from a fire hose and putting off anomalies to study later is that you often don't get around to it," Wennberg said. Within six months, NASA had confirmed Farman's work, he said.

During the 1990s, "the ozone hole continued to get broader and deeper. It seems that 2,000 parts of chlorine per trillion is what we have to get back to if we want to stop depletion of the ozone level. Estimates show that it will take until 2050 to reach that level," Wennberg said.

Although complete success is far in the future, current evidence shows movement in the right direction.

"Monitoring is taking place all over the world. We're now down 5 percent from where we were in 1999. The Montreal conventions are working and concentrations of chlorine are coming down," Wennberg said.

"Had we not taken action, by 2040 the UV dose would have doubled over most of the globe. Science and policy worked together to avert a near catastrophe."


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