Oct. 7, 2003 — This year's Antarctic ozone "hole" is the second largest ever observed, according to NOAA scientists. The size of the ozone depletion region shows an increase in its total size from last year, further indicating that the relatively smaller hole of 2002 was mostly a quirk of meteorological conditions over Antarctica. The difference is directly attributed to year-to-year temperature variations across the Antarctic continent, not an increase in the amount of ozone-depleting compounds in the atmosphere. "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 L. Albritton, director of the NOAA Aeronomy Laboratory in Boulder, Colo.
The Antarctic ozone "hole" is defined as thinning of the springtime ozone layer to levels significantly below those seen prior to 1979. 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.
Chlorine- and bromine-containing compounds from human activity are the primary cause of ozone depletion. The 1987 United Nations Montreal Protocol and its subsequent amendments sharply curtailed the use of chlorine-containing chlorofluorcarbons (CFCs) 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.
"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 the NOAA 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." NOAA provides predictions of expected levels of ultraviolet radiation in support of the Environmental Protection Agency's Sunwise program.

At South Pole Station, balloon-borne ozone-measuring instruments launched by the NOAA 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 Sept. 26 showed nearly complete ozone destruction in the 9-13 mile altitude layer. Total column ozone indicated a 60 per cent drop from early August measurements.
"This year, ozone depletion over the South Pole, from 7-to-14 miles above Antarctica, has shown large losses, similar to losses seen in the 1990s," said Bryan Johnson of the NOAA Climate Monitoring and Diagnostics Laboratory.
Ozone blocks harmful ultraviolet "B" rays. Prolonged over-exposure to ultraviolet radiation has been linked to skin cancer in humans and other adverse biological effects on plants and animals. The dramatic ozone "hole" exists only over Antarctica, but currently, the ozone layer over the United States is depleted by about 6 percent.
Temperature over the Antarctic affects the formation of polar stratospheric clouds, which accelerate the destruction of stratospheric ozone by human-produced chlorine and bromine compounds. The Antarctic ozone hole is still expected to recover in about 50 years, when the atmospheric amounts of reactive chlorine and bromine return to their pre-ozone-hole levels.
The observed size of the ozone depletion region in 2003 is a stark 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 Sept. 11, 2003, smaller than Sept. 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.

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Relevant Web Sites
NOAA Meteorological Conditions and Ozone in the Polar Stratosphere
NOAA Monitors Stratospheric Ozone
NOAA South Pole Ozone Program
NOAA 2003 Southern Hemisphere Ozone Hole Area

Media Contact:
Carmeyia Gillis, NOAA Climate Prediction Center, (301) 763-8000 ext. 7163