Edition: U.S. / Global

New Evidence Ties Ozone Hole to Human Activity

Published: December 20, 1994

NASA scientists provided fresh evidence today that chlorines produced by human activity are chiefly responsible for eating away Earth's protective layer of ozone.

Detailed data sent back to Earth since 1991 by the orbiting Upper Atmosphere Research Satellite, the largest environmental monitor ever built, prove what NASA and other scientists have long suspected: the ozone hole is caused by chlorofluorocarbons, or CFC's, according to the National Aeronautics and Space Administration.

By process of elimination, NASA scientists found that the ozone-destroying acids detected by the satellite could only be caused by industrial gases since they do not occur naturally. CFC's, which are being phased out slowly under international agreements, are used as antifreeze, insulation and as refrigerants. Their common ingredient is chlorine.

"CFC's are responsible for the ozone hole," Dr. Mark Schoeberl, satellite project scientist, told a news conference at the Goddard Space Flight Center in suburban Maryland.

The ozone layer acts as a shield against potentially damaging ultraviolet rays from the Sun. If these rays should reach the surface of Earth at intense levels, they could cause crop damage, cancers and cataracts.

No one is certain how long the hole in the ozone layer that occurs each winter over the South Pole has been in existence. It was first detected in 1979.

Scientists fear that too much ozone depletion could send the swirling hole northward over more populated tropical and mid-latitude areas. NASA satellite photos show that the hole extends from the pole to the southern tip of South America.

Cold temperatures over the pole form ice clouds that lead to converting chlorine into ozone-eating chlorine monoxide. In turn, circular winds create a swirling "hole" that draws in more ozone. One atom of chlorine can destroy 10,000 to 100,000 ozone molecules.