GENEVA, Switzerland – The ozone layer has recovered at the poles, but the lower stratospheric ozone over the most populated latitudes has declined, according to a study published on Tuesday in the scientific journal Atmospheric Chemistry and Physics.
An international team headed by ETH Zurich University and the Physikalisch-Meteorologisches Observatorium Davos, have discovered that despite the ban on chlorofluorocarbons (CFCs), the concentration of ozone in the lower part of the stratosphere has continued to decline.
The study threw up unexpected results, because scientific models did not predict the decline, leading scientists to believe the ozone layer would fully recover by 2050.
Researchers used satellite measurements spanning the last three decades together with advanced statistical methods and data from centers in the United Kingdom, the United States, Canada and Finland, as well as information provided by NASA.
“The finding of declining low-latitude ozone is surprising, since our current best atmospheric circulation models do not predict this effect. Very short-lived substances could be the missing factor in these models,” William Ball, ETH researcher and head of the study, said.
Ball added that ozone had increased significantly in the upper layers of the stratosphere and the polar regions were recovering thanks to the Montreal Protocol, signed in 1987.
The ozone forms in the Earth’s atmosphere from the photo dissociation of molecular oxygen, primarily in the tropical stratosphere.
It is then transported to the middle latitudes beyond the tropics, forming a protective “ozone layer” around the globe.
A large portion of the resulting ozone stays in the lower stratosphere and absorbs UV rays from the sun because, if they reach the surface of the Earth, they could damage the DNA of plants, animals and humans.
The researchers said the new findings are a concern but stopped short of saying they were alarming, pointing to the drastic improvements achieved since the Montreal Protocol.
Joanna Haigh, co-director of the Grantham Institute at Imperial College London in the United Kingdom, warned that the potential for harm in lower latitudes may actually be worse than at the poles, given that the UV radiation is more intense in these areas and they are more populated.
The study concluded that efforts should now focus on obtaining more accurate information on ozone depletion.