October 1, 2002

U.S. atmospheric scientists report that the ozone hole over the Antarctic is much smaller than it was the past two years, and split into two separate holes during late September. The scientists stress that the smaller hole is due to this year’s peculiar weather patterns and may not be an indication that the ozone layer is recovering.

According to a September 30 press release, instruments aboard satellites operated by the National Aeronautics and Space Administration (NASA) and the National Oceanic and Atmospheric Administration (NOAA) estimate the area of the Antarctic ozone hole to be around 15 million square kilometers, well below the more than 25 million square kilometers observed during the past six years for the same time of year.

Researchers say that warmer than normal temperatures this year around the edge of the polar vortex that forms annually in the upper atmosphere over Antarctica are responsible for the smaller ozone loss. The last time the ozone hole was as small as it is this year was in 1988, and that was also due to warm temperatures.

The ozone layer prevents much of the sun’s harmful ultraviolet radiation from reaching the Earth’s surface. Recognition of the damage to the ozone layer led to international adoption of the Montreal Protocol in 1995and its amendments banning chlorine-containing chlorofluorocarbons (CFCs) and bromine-containing halons because of their destructive effect on the ozone layer.

Scientists also said that the Southern Hemisphere’s upper atmosphere was unusually disturbed this year, and that the weather patterns were so strong that the ozone hole split into two pieces during late September. "This is the first time we’ve seen the polar vortex split in September," said Craig Long, meteorologist at the NOAA Climate Prediction Center.

Ozone depletion occurs only at very low temperatures under the influence of solar radiation. The coldest temperatures over the South Pole typically occur in August and September. Thin clouds form in these cold conditions, and chemical reactions on the cloud particles help human-made chlorine and bromine chemicals rapidly destroy the ozone layer. Even though banned under the Montreal Protocol, CFCs and halons are extremely long-lived and still linger at high concentrations in the atmosphere.