In a little over three decades, world communities have come together for a historic agreement to keep the hole in the ozone layer from growing. This international treaty, known as the Montreal Protocol, has banned the use of harmful chemicals that adversely affect the Earth's natural ozone barrier, which in turn protects us from the sun's ultraviolet radiation.
A recently published article in the European Society of Geophysical Sciences journal Atmospheric Chemistry and Physics suggests that ozone recovery at lower latitudes is not going as expected. In particular, the ozone layer at mid and low latitudes, where most people live, is showing unexpected declines for reasons that are still unclear.
Today it is lower than 20 years ago, which is important because the data obtained does not correspond to what our models of atmospheric processes that should occur in the lower layers of the stratosphere suggest.
The results obtained may be indicative of a problem with the inaccuracy of the atmospheric circulation models that have been used so far. But the ozone layer can also get thinner as ozone-depleting substances such as chlorine and bromine, which are not regulated under the Montreal Protocol, reach the stratospheric ozone layer.
Scientists speculate that the participation of so-called "very short-lived substances", such as chlorine and bromine, were previously ignored because they did not have to exist long enough in a free state to reach the ozone layer. Therefore, the researchers propose to correct the existing models of the Earth's atmosphere circulation, taking into account the assumed factors.
So far, only one thing is clear: the still unexplained decrease in ozone at low latitudes should not be taken as a failure of the Montreal Protocol, thanks to which by 2030 there will be a million fewer skin cancers per year. The Protocol also helps to combat climate change: from 1989 to 2013, the measures in place helped to avoid emissions of pollutants in the amount of 135 billion tons. This is equivalent to about 5.6 billion tonnes of CO2 emissions per year.
Scientists believe that further action against climate change under the Montreal and Paris Climate Agreements must continue. At the very least, constant monitoring of both the ozone layer and the Earth's atmosphere as a whole is required, since new unexpected environmental factors may appear that are not taken into account by existing climate models.
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