Last year's severe winter in the northern hemisphere depleted the earth's ozone to such record levels that scientists say the loss can "reasonably be described as an Arctic ozone hole."

A study published in the British journal Nature suggests the trigger was an annual polar vortex, a large-scale cyclone over the Arctic, which last year was formed in extremely cold conditions and created a hole roughly five times the size of Germany.

In April, the hole moved over parts of eastern Europe, Russia and Mongolia and exposed populations to higher levels of harmful ultra-violet (UV) light.

When intact, the earth's ozone reduces levels of UV light coming through to earth, which can otherwise damage vegetation, and cause skin cancer and cataracts.

Satellite technology tracked the ozone hole over Europe

A challenge to accepted theories

Chemical ozone destruction happens every year over both of the earth's polar regions - the Arctic in the north and Antarctic in the south.

Ozone loss in the Antarctic tends to be worse because it generally gets colder there.

And until now, analysis of the Arctic has suggested that the loss, while variable, is far more limited.

But measurements taken by satellite during the 2010-2011 Arctic winter-spring found the ozone badly depleted at a height of between 15 and 23 kilometers (9.3 and 14.3 miles).

The highest level loss was found between 18 and 20 kilometers and amounted to more than 80 percent.

"The ozone destruction began in January," Gloria Manney, one of the authors of the study at the Jet Propulsion Laboratory in California, told the AFP news agency, "[and] ozone values in the polar vortex region were much lower than usual from early March through late April - after which the polar vortex dissipated."

Back to the 80s

The Arctic ozone hole spread over an area of about two million square kilometers (777,000 square miles) and was observed for about 27 days. Its size was similar to the ozone loss seen in Antarctica in the mid-1980s.

But Manney said the higher exposure to UV light had not been constant because the vortex moved every day until it faded.

While the study suggests this year's Arctic ozone hole was caused by a deep chill over the North Pole, ozone holes have also been caused by the use of man-made chlorine-based compounds that were once common in refrigerants and aerosols.

Author: Zulfikar Abbany

Editor: Michael Lawton