Ozone layer keeps thinning out despite decades of protection: study

GENEVA, Feb. 6 (Xinhua) -- Contrary to recent scientific assumptions, the ozone layer, which protects life on the Earth from harmful ultra-violet radiation, continues to deplete on a global scale even after decades of efforts to protect it, according to an international study on Tuesday.

The study, by a team of scientists led by researchers in Zurich, was published on Tuesday in the journal Atmospheric Chemistry and Physics. Scientists have demonstrated the results by using satellite measurements spanning the past 30 years combined with advanced statistical methods.

The ozone thinning process began in the 20th century when excessive quantities of chemicals, including chlorofluorocarbons (CFCs), were released into the atmosphere. These substances were banned in 1989 in accordance with the Montreal Protocol and since then the ozone layer in the upper stratosphere has recovered significantly, particularly in the polar regions.

However, total ozone levels in the atmosphere remained the same and now scientists at the federal institute of technology ETH Zurich showed that this is because ozone in the lower stratosphere declined steadily over the past three decades.

In November 2015, for instance, scientists measured the solar radiation at the Glaciar Union camp in the Antarctica, found that the ozone hole reached a record size with 10 squared kilometers, more than the double of the average of the season.

William Ball, an atmospheric researcher at ETH Zurich and the first author of the study, explains that this had been so difficult to demonstrate, because so-called "summer smog" caused by human activity "masks the stratospheric decline in the satellite measurements."

Scientists are not yet sure what accounts for this continuing decline, but one explanation could be that climate change modifies the pattern of atmospheric circulation. Chemicals of industrial origin released into the atmosphere could also be responsible for the development.

Substitutes for the particularly harmful CFCs are less thinning for the ozone layer but are not neutral either. These chemicals could so far have been "an insufficiently considered factor in the models," said Ball.

Nevertheless, scientists said these new findings were "concerning but not alarming," as more research now needs to be done in order to monitor and investigate the causes behind the continuing ozone decline in the lower stratosphere. Enditem