The sun and some sundogs blaze over a research camp in Antarctica. The ozone layer usually shields the Earth from the sun's ultraviolet light, but a hole in the ozone forms each spring above Antarctica. (Photo submitted by Stefan Elieff/Sander Geophysics)

The depletion of the ozone layer has levelled off, and the amount of the UV-filtering gas has slightly increased over the last decade, European scientists say.

The finding is the result of compiling ozone measurements from several European and American satellites from 1979 to 2008.

The researchers from Chalmers University of Technology in Gothenburg, Sweden, combined the readings of several instruments on NASA and European satellites, some of which look vertically down to the ground, and others that look sideways at the layers of the Earth's atmosphere.

Jo Urban of Chalmers said their analysis shows a decline in ozone in the upper stratosphere of about seven per cent per decade between 1979 and 1997.

"A clear statistically significant change of trend can be seen around 1997," said Urban, in a release.

After 1997, Urban said, a small increase of about one per cent per decade was found, although statistically that increase was not significantly different from no change at all.

The results were presented as part of the European Space Agency's conference on atmospheric science in Barcelona in September.

Ozone, a bluish gas composed of three oxygen atoms, is harmful to breathe, but absorbs ultraviolet radiation that harms living organisms. Its presence in our stratosphere helps keep harmful UV rays originating from the sun from reaching the Earth.

The thinning ozone layer increases the risk of skin cancer and cataracts.

A hole in the ozone layer over Antarctica typically reaches its maximum size in September or early October, and then dissipates into smaller parts throughout southern latitudes, affecting the UV exposure in places such as New Zealand, Australia and South America.

NASA and the ESA have been monitoring the depletion of ozone through satellite observations since the 1970s. The increasing size of the hole in the 1980s was the motivation behind restrictions on the use of chlorofluorocarbons, or CFCs, introduced in the Montreal Protocol.