Ozone Depletion at the Poles: The Hole Story Emerges

Last August, in the dark of the Antarctic winter, more than 100 scientists descended to the southern tip of the globe, some to monitor the stratosphere from airplanes flying high above Antarctica, others to sample it with balloons and remote sensing equipment from ground stations on the continent. The massive assault was an urgent effort to determine the cause of the ozone hole—the depletion of ozone in the lower stratosphere that has occurred with increasing severity each spring since the mid‐1970s. After analyzing their data, these scientists reconvened last May in Snowmass, Colorado, to present for the first time all the details of their findings. The extensive new data leave no doubt that man‐made chlorofluorocarbons are primarily responsible for the ozone hole. They elucidate more clearly than ever before the unique wintertime meteorological conditions that allow chlorine compounds from these CFCs to destroy virtually all the ozone in the lower stratosphere over the Antarctic: The ice clouds that form in the dry, frigid stratosphere seem to facilitate chemical reactions that free chlorine atoms from those compounds in which they are normally trapped. The freed chlorine atoms can then ravage the ozone. Although this general hypothesis was gaining wide support even before the recent expedition, the new data put it on firmer grounds and allow the specialists to start filling in the details.