Severe weather has caused an ozone hole five times the size of California over the Arctic, setting a record in matching ozone loss over Antarctica, scientists say.
About 13 miles above the ground, 80% of the ozone was lost, BBC reports.
A harsh chill over the North Pole at altitude caused the unprecedented hole which for two weeks moved over eastern Europe, Russia and Mongolia, exposing populations to higher, but unsustained, levels of ultraviolet light, it reports.
The long spell of cold conditions meant the chlorine chemicals that destroy ozone - once widely used in refrigerants and consumer aerosols - are at their most active, AFP reports.
Ozone loss is worse over the Antarctic because of the much colder temperatures.
"For the first time, sufficient loss occurred to reasonably be described as an Arctic ozone hole," said the study, appearing in the British science journal Nature.
It is not possible to know whether such a loss will occur again, it says.
A similar ozone loss occurred in Antarctica in the mid-1980s.
The study challenges conventional wisdom on the Arctic's susceptibility to ozone holes, which is based on limited studies of satellite observations, AFP reports.
Stratospheric temperatures in the Arctic have been extraordinarily varied in the past decade, the paper notes.
Four out of the past 10 years have been among the warmest in the past 32 years, and two are the coldest, AFP reports.