Antarctic ozone hole biggest on record, U.S. reports
Thu Oct 19, 2006 3:40 PM ET
WASHINGTON (Reuters) – This year’s ozone hole over Antarctica is bigger and deeper than any other on record, U.S. scientists reported on Thursday.
The ozone layer shields Earth from the sun’s harmful ultraviolet rays, and the layer thins out over the South Pole each year, primarily because human-made compounds release ozone-eating chlorine and bromine gases into the stratosphere.
“From September 21 to 30, the average area of the ozone hole was the largest ever observed, at 10.6 million square miles ,” said Paul Newman of NASA’s Goddard Space Flight Center outside Washington.
If the stratospheric weather conditions had been normal, the ozone hole would be expected to reach a size of about 8.9 million to 9.3 million square miles, about the surface area of North America, NASA said in a statement.
Scientists measure the total amount of ozone from the ground to the upper atmosphere in Dobson Units, and a NASA satellite detected a low level of 85 Dobson Units on October 8 of the East Antarctic ice sheet.
Scientists from the National Oceanic and Atmospheric Administration used balloon-borne instruments to measure ozone right over the South Pole, and by October 9 the total ozone in a column from the ground to the upper atmosphere had dropped to 93 DU from about 300 DU in mid-July.
Temperature variations in the Antarctic stratosphere causes the severity of the ozone hole to vary from year to year. Colder temperatures result in larger and deeper ozone holes, while warmer temperatures lead to smaller ones. This year, the lower stratosphere was about 9 degrees Fahrenheit (5 degrees Celsius) cooler than average.
Concentrations of ozone-depleting chemicals in the lower atmosphere have been declining since 1995, and scientists estimate the ozone hole will be completely recovered by about 2065.