Stratospheric ozone loss in the Arctic has this year reached a level never observed before in the northern hemisphere.

Observations made since January from the ground and from balloons show that 40% of ozone molecules have been destroyed over the Arctic. The highest ozone loss previously measured in early spring, when ozone depletion reaches its maximum, was 30% in 2005. Nature first reported on this last month.

Scientists with the World Meteorological Organisation and the Alfred Wegener Institute of Polar and Marine Research (AWI) released the figures today at the general assembly of the European Union of Geosciences in Vienna.

There was a palpable sense in the EGU press room that the Arctic has indeed experienced its first-ever full-fledged ozone hole – massive ozone loss previously only observed over colder Antarctica.

“It’s a fair question to ask if there’s any difference left between seasonal ozone depletion in the Arctic and in Antarctica,” says Markus Rex, an ozone researcher with AWI.

“It’s unprecedented, but not totally unexpected,” says Geir Braathen of the WMO’s atmospheric environmental research division.

The main reason for the record ozone loss this year is that unusually cold stratospheric temperatures, extending until late in the season, have favoured the formation of polar stratospheric clouds. The catalytic chemical destruction of ozone molecules occurs on the surface of these clouds which form at 18-25 kilometres height when temperatures drop below -78 C.

Ozone-depleted air has in the past few weeks reached Scandinavia and northern China. More densely populated areas in Europe, Asia and North America have been spared so far, but an excursion of ozone-depleted air to mid-latitudes could still happen any time in the next two weeks or so.

The stratospheric ozone layer absorbs the bulk of harmful UV-B radiation reaching the Earth. Current conditions mean that, unprotected, people might get sunburned in 20-30 minutes.

“It’s not dramatic, but people do need to know this,” says Rex.

The phasing out of ozone-destroying chemicals since 1987 has so far merely led to an average 10% or so recovery of the polar ozone layers. Stratospheric ozone is not expected to fully recover to 1980 levels before the end of the century.

Image 1: CRNS. Image 2: Location of Arctic polar vortex on April 4, 2011 / AWI