OneWorld.net (U.S.)

BOULDER, Colorado, October 8, 2003 (ENS) - This year's Antarctic ozone hole is the second largest ever observed, say scientists from three U.S. federal agencies. The size of the ozone depletion shows an increase in total size from last year, indicating that the smaller hole of 2002 was due to "a quirk of meteorological conditions over Antarctica."

Researchers from the National Oceanic and Atmospheric Administration (NOAA), the National Aeronautics and Space adminstrator (NASA), and the Naval Research Laboratory made the observations.

"This year, ozone depletion over the South Pole, from seven to 14 miles above Antarctica, has shown large losses, similar to losses seen in the 1990s," said Bryan Johnson of NOAA's Climate Monitoring and Diagnostics Laboratory.

The difference is a result of "year-to-year temperature variations across the Antarctic continent, not an increase in the amount of ozone-depleting compounds in the atmosphere," the agencies said.

"We expect to see year-to-year variations in the size of the ozone hole, because stratospheric temperatures can vary from year to year. In colder years, the same amount of ozone-depleting compounds can destroy more ozone, in comparison to warmer years," said Daniel Albritton, director of the NOAA Aeronomy Laboratory in Boulder.

The observed size of the ozone depletion region in 2003 is a contrast from 2002. The reduced size in 2002 was attributed to warmer than normal stratospheric temperatures and temperature patterns above Antarctica.

The size of this year's Antarctic ozone hole reached 10.9 million square miles on September 11, 2003, smaller than September 10, 2000, the largest ever recorded when it covered 11.5 million square miles. Last year the ozone hole was smaller, covering 8.1 million square miles.

Extreme cold in the upper atmosphere is one key factor that affects the amount of ozone loss caused by ozone depleting compounds. Year-to-year changes in the size and amount of depletion in the vertical column of the ozone hole are dominated by the year-to-year variations in temperature in this part of the atmosphere, the researchers say. "Although international protocols have greatly reduced the production and release of ozone depleting chemicals, they will remain active in the stratosphere for several decades," said James Laver, Director of NOAA's Climate Prediction Center. "With the protective atmospheric layer so compromised, greater amounts of ultraviolet radiation may be allowed to reach the surface and potentially increase certain health risks."

Compounds containing chlorine and bromine from human activity are the primary cause of ozone depletion. The 1987 United Nations Montreal Protocol limited the use of chlorofluorcarbons and bromine containing halons.

Because of the protocol, the amounts of these ozone depleting substances have begun to decline in the lower atmosphere and to level off in the stratosphere, where the ozone layer resides, the scientists have observed.

At South Pole Station, balloon borne ozone measuring instruments launched by NOAA's Climate Monitoring and Diagnostics Laboratory reveal the vertical structure of the developing ozone hole. An important gauge for identifying when future recovery of the Antarctic ozone hole begins is the severity of depletion observed in the upper atmosphere near the main ozone layer.

Ozone measured by a balloon instrument on September 26 showed nearly complete ozone destruction in the nine to 13 mile altitude layer. Total column ozone indicated a 60 percent drop from early August measurements.

The Antarctic ozone hole is still expected to recover in about 50 years, the scientists said, when the atmospheric amounts of reactive chlorine and bromine return to their pre-ozone hole levels.

Ozone blocks harmful ultraviolet B rays from the Sun. Prolonged overexposure to ultraviolet radiation has been linked to skin cancer in humans and other adverse biological effects on plants and animals.

The ozone hole exists only over Antarctica, but currently, the scientists say, the ozone layer over the United States is depleted by about six percent.

Copyright Environment News Service (ENS) 2003. All Rights Reserved.