THE OZONE LAYER | hole absorbed faster than expected

The hole in the ozone layer decreases, and even faster than expected, announced a US scientific study published in the journal Science. Yet the problem is not yet resolved. Explanations with a specialist.

This is good news for the planet. The hole in the ozone layer is absorbed. Researchers, whose work was published Thursday in the famous journal Science, calculated that fell over four million km2 - roughly the size of the European Union - since 2000, when the phenomenon was at its highest level. Their study is based on measurements taken for fifteen years.

A suprise. "I did not think it would be too early," admitted Susan Solomon, professor of chemistry and climate science at the Massachusetts Institute of Technology - US academic research institute particularly renowned - the origin of the work.

"Overall the ozone hole appears to be on the road to recovery," the scientists conclude. They estimated that full recovery could be expected by 2050.

The responsible human activity

In the mid-1980s, scientists have found that the total amount of ozone decreased sharply over Antarctica. The hole in the ozone layer, gaseous shield protecting the Earth from ultraviolet solar radiation (UV), was discovered by analyzing readings from ground station dating back to the 1950s.

"It's not really a hole, according to BFMTV.com Slimane Bekki, research director at CNRS. Ozone is always present but the layer is very thin."

At the end of the southern winter and early spring, that is to say the end of August to October, the ozone layer is destroyed half on an altitude of 15-25 km. And it is human activity that is responsible. The reason: chemicals, including chlorofluorocarbons (CFCs). Since the late 1990s, the ozone concentration decreased by 15% on a total area of ​​20 million square kilometers, more than the Arctic Ocean.

"CFCs have a long life, between fifty and a hundred years, says Slimane Bekki. At 30 km altitude, these molecules decompose under the effect of UV radiation. They then release chlorine and bromine, which destroy the ozone layer."

The Montreal Protocol signed in 1987

To limit the phenomenon, the Montreal Protocol was signed in 1987. This international treaty foresaw the progressive ban of these gases. Atmospheric concentrations decreased by 10-15% compared to the peak of the late 1990s, according to the latest report by the World Meteorological Organization and the United Nations Environment Programme published in 2015.

"CFCs are man-made compounds that were synthesized in the middle of the last century, advanced Slimane Bekki, co-author of the report. They have developed rapidly, finding industrial applications in aerosols, fire extinguishers, refrigeration systems or air conditioning. at the time, it was not known that molecules expressed on the surface could be carried aloft. "

A phenomenon linked to climate change

Yet the battle is not yet won and the phenomenon could even grow in other parts of the globe.

"A decrease of the ozone layer over the place, Slimane Bekki remark. It is especially in the tropics, where the ozone layer is already very low, that the phenomenon is projected seems s' accelerate."

But in this case, the charge would be climate change, which could aggravate the phenomenon under the influence of greenhouse gases.