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Many people are reducing their risks. In Punta Arenas, Chile's southernmost city, some parents keep their children indoors between 10 a.m. and 3 p.m., and soccer practice has been moved from midafternoon to later in the day. The Australian government issues alerts when especially high UV levels are expected, and public-service campaigns warn of the dangers of sunbathing, much as U.S. ads counsel people not to smoke. In New Zealand schoolchildren are urged to wear hats and eat their lunches in the shade of trees.
Scientists are also concerned about the potential effect of ozone depletion on the earth's climate systems. When stratospheric ozone intercepts UV light, heat is generated. That heat helps create stratospheric winds, the driving force behind weather patterns. Says Sherwood Rowland, a chemist at the University of California at Irvine, who first discovered the dangers of CFCs: "If you change the amount of ozone or even just change its distribution, you can change the temperature structure of the stratosphere. You're playing there with the whole scheme of how weather is created."
Weather patterns have already begun to change over Antarctica. Each sunless winter, steady winds blow in a circular pattern over the ocean that surrounds the continent, trapping a huge air mass inside for months at a time. As the sun rises in the spring, this mass, known as a polar vortex, warms and breaks up. But the lack of ozone causes the stratosphere to warm more slowly, and the vortex takes longer to dissipate. This leads to even more ozone destruction: the polar vortex acts as a sort of pressure cooker to intensify chlorine's assault on ozone molecules.
When Rowland and his colleague, Mario Molina, issued the first ozone alert back in 1974, they had no idea that depletion would be particularly severe in Antarctica or in any other part of the world. What they did predict was that CFCs would not disintegrate quickly in the lower regions of the atmosphere. Instead the hardy chemicals would rise into the stratosphere before dissociating to form ClO and other compounds. The highly reactive chlorine would then capture and break apart ozone molecules. Each atom of chlorine, it was later determined, could destroy up to 100,000 molecules of ozone -- at a far faster rate than the gas is replenished naturally.
But Rowland and Molina had deduced only the broadest outlines of the process. The details had to wait until the mid-1980s, when atmospheric scientists realized belatedly that while worldwide ozone levels had declined somewhat, there was an enormous deficit in Antarctica every year. Determined to understand whether CFCs were the culprit, NASA mounted a series of flights from Punta Arenas into the Antarctic in 1987. They revealed unusually high concentrations -- up to 1 part per billion -- of ClO. They had found the smoking gun Rowland and Molina had predicted.