The protective ozone layer in the Arctic that keeps out the sun's most damaging rays — ultraviolet radiation — has thinned about 40 percent this winter, a record drop, the U.N. weather agency said Tuesday.
The Arctic's damaged stratospheric ozone layer isn't the best known "ozone hole" — that would be Antarctica's, which forms when sunlight returns in spring there each year. But the Arctic's situation is due to similar causes: ozone-munching compounds in air pollutants that are chemically triggered by a combination of extremely cold temperatures and sunlight.
The losses this winter in the Arctic's fragile ozone atmospheric layer strongly exceeded the previous seasonal loss of about 30 percent, the U.N.'s World Meteorological Organization in Geneva said.
It blamed the combination of very cold temperatures in the stratosphere, the second major layer of the Earth's atmosphere, just above the troposphere, and ozone-eating CFCs from aerosol sprays and refrigeration.
"This is pretty sudden and unusual," said Bryan Johnson, an atmospheric chemist who works in the U.S. National Oceanic and Atmospheric Administration's Earth System Laboratory in Boulder, Colorado.
Atmospheric scientists concerned about global warming focus on the Arctic because that is a region where the effects are expected to be felt first.
This year, the Arctic winter was warmer than average at ground level but colder in the stratosphere than normal. Average Arctic temperatures in January range from about -40 to 0 C (-40 to 32 F) and in July from about -10 to 10 C (14 to 50 F).
U.N. officials say the latest losses — unprecedented, but not entirely unexpected — were detected in satellite observations and weather balloons that show at what altitudes the ozone loss is occurring.