Antarctic ozone hole has split in two and shrunk

WASHINGTON -- The ozone hole over Antarctica is markedly smaller this year than in the last few years and has split in two, government scientists reported Monday.

The so-called "hole," actually an area of thinner than normal ozone, was measured at 6 million square miles in September. That compares with around 9 million square miles on September measurements over the last six years, according to researchers at the National Oceanic and Atmospheric Administration and National Aeronautics and Space Agency.

While ozone at ground level is considered a pollutant, the layer of ozone high in the stratosphere is vital to life because it blocks dangerous radiation coming from the sun. Thinning of the ozone layer could lead to a rise in skin cancer, experts warn. Aerosols and other chemicals are blamed for the thinning, and treaties banning those ingredients are expected to help the layer recover over time.

This year's improvement was attributed to warmer than normal temperatures around the edge of the polar vortex, or circular wind pattern that forms annually in the stratosphere over Antarctica, according to Paul Newman, a lead ozone researcher at NASA's Goddard Space Flight Center in Greenbelt, Md.

Craig Long, a meteorologist at the NOAA Climate Prediction Center, said the stratosphere over the southern hemisphere was unusually disturbed this year by the wind, causing the hole to split into two separate holes.

In 2001 the Antarctic ozone hole reached a maximum size of more than 10.2 million square miles, larger than the entire area of North America, including the United States, Canada and Mexico combined. In the year 2000, it briefly approached 11.5 million square miles. 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.

Thin clouds form

Newman explained that while "chlorine and bromine chemicals cause the ozone hole, the temperature is also a key factor in ozone loss."

The coldest temperatures over the South Pole occur in August and September. Thin clouds form in these cold conditions, and chemical reactions on the cloud particles help chlorine and bromine gases to rapidly destroy ozone. By early October, temperatures typically start to warm and the ozone layer starts to recover.

An Australian study published two weeks ago reported that chlorine-based chemical levels in the atmosphere are falling, and the hole in the ozone layer should close within 50 years.

Although the ozone layer has not yet begun to repair itself, the hole would probably start closing within five years, said Paul Fraser, of the Australian government-funded Commonwealth Scientific and Industrial Research Organization, or CSIRO.