Researchers have seen the worst loss of ozone yet recorded over the Arctic, as bad as the loss that causes the ozone hole over the Antarctic every year, NASA said on Sunday.
Cold temperatures in the stratosphere seem to have caused the ozone depletion last winter and spring, NASA scientists and others reported in the journal Nature.
The ozone layer helps protect the Earth's surface from the sun's damaging rays. Chemicals such as chlorofluorocarbons can react with ozone to break it down.
Usually the damage isn't so bad over the Arctic. But this past year's destruction over the Arctic matches that seen in some years over the Antarctic, where an ozone "hole" has formed each spring since the mid-1980s.
Scientists from the United States, Germany, the Netherlands, Canada, Russia, Finland, Denmark, Japan, and Spain analyzed measurements from two NASA spacecraft, weather balloons, and other sources for the study.
At some altitudes, cold stratospheric temperatures that cause the ozone destruction lasted more than 30 days longer in 2011 than in any Arctic winter ever studied before, they said.
"This implies that if winter Arctic stratospheric temperatures drop just slightly in the future, for example as a result of climate change, then severe Arctic ozone loss may occur more frequently," said Gloria Manney of NASA's Jet Propulsion Laboratory in Pasadena, Calif.
It's not clear why the air was so cool over the Arctic this year, but scientists are checking.