Study Finds Drop in Ozone Level Worse Than Expected

Man-made chemicals have shrunk the Earth’s protective ozone layer by about 2.3% over most of the United States since 1969, and by significantly larger amounts near the north and south poles, scientists disclosed today in a long-awaited report.

The average ozone depletion over Australia and New Zealand is even higher, about 4%--large enough to cause at least a 20% increase in skin cancer in those areas over the next two decades, researchers said in the report issued by the National Aeronautics and Space Administration. The depletion may already be decreasing agricultural and fishery productivity in most temperate regions of the world, they added.

Chemical Release Blamed

Researchers said there is little doubt that the ozone depletion is due to the continued release of the destructive chemicals, called chlorofluorocarbons or CFCs, which are widely used in refrigerators and air conditioners as well as for the production of plastic foams. CFC molecules, when exposed to sunlight, can destroy ozone molecules in the stratosphere, the segment of the atmosphere extending from about 9 miles to 30 miles above the Earth’s surface.

Ozone molecules in the stratosphere absorb more than 99% of the ultraviolet radiation emitted by the sun, thereby protecting life on Earth from its destructive effects. When the CFCs destroy the ozone, more ultraviolet radiation reaches the Earth.

Disturbing Discovery

Perhaps most disturbing, the researchers said, is that the decrease in ozone is more than twice as large as scientists had expected when they began the study 17 months ago. This indicates the long-term effects of CFCs on ozone depletion may be much worse than previously believed.

The new report was issued one day after the Senate, by a vote of 83 to 0, ratified a treaty that would reduce future production of CFCs by 50% by the end of the century. Representatives of 46 nations agreed to the treaty in September in Montreal, but the United States will be the first large CFC-producing country to ratify it when President Reagan signs it.

The most recent projections, made by NASA in 1985, said that the average amount of ozone in the stratosphere would fall between 4.9% and 9.4% during the next century, with the greatest decreases occurring at high latitudes.

Estimates May Be Low

Based on the new results reported today, those estimates may be much too low, said UC Irvine chemist F. Sherwood Rowland, who headed one of the panels that prepared the report.

Scientists have predicted that every 1% decrease in ozone in the stratosphere will cause a 5% to 6% increase in skin cancers.

The new study was prompted by two “startling” developments, said NASA’s Robert Watson. The first was the discovery by British scientists in 1979 of a “hole” in the ozone layer over Antarctica every austral spring.

The “hole”--which is actually a short-term depletion of ozone by as much as 50% over an area larger than the United States--has shown a greater depletion and has persisted longer each year since 1979.

The second development was data from satellite instruments that suggested that the ozone layer was being depleted at a rate as great as 1% a year.

The new study, carried out by more than 100 scientists over a period of 17 months, used data from ground-based ozone detectors to calibrate the satellite data. The researchers concluded that the satellite instruments were deteriorating and showed a much greater ozone depletion than was actually occurring, Watson said.