NASA scientists say that ozone layer might recover in the future, thanks to the changing climate and atmospheric circulation.
According to the scientists, Earth's ozone layer should eventually recover from the unintended destruction brought on by the use of chlorofluorocarbons (CFCs) and similar ozone-depleting chemicals in the 20th century, since greenhouse gases are changing the dynamics of the atmosphere.
Previous studies have shown that while the buildup of greenhouse gases makes it warmer in troposphere, the level of atmosphere from Earth's surface up to 10 kilometers (6 miles) altitude, it actually cools the upper stratosphere, between 30 to 50 kilometers high (18 to 31 miles).
This cooling slows the chemical reactions that deplete ozone in the upper stratosphere and allows natural ozone production in that region to outpace destruction by CFCs.
But, the accumulation of greenhouse gases also changes the circulation of stratospheric air masses from the tropics to the poles, according to NASA scientists.
In Earth's middle latitudes, that means ozone is likely to "over-recover," growing to concentrations higher than they were before the mass production of CFCs.
In the tropics, stratospheric circulation changes could prevent the ozone layer from fully recovering.
"Most studies of ozone and global change have focused on cooling in the upper stratosphere," said Feng Li, an atmospheric scientist at the Goddard Earth Sciences and Technology Center at the University of Maryland Baltimore County, Baltimore, Maryland, and lead author of the study.
"But, we find circulation is just as important. It's not one process or the other, but both," he added.
The findings are based on a detailed computer model that includes atmospheric chemical effects, wind changes, and solar radiation changes.
Working with Richard Stolarski and Paul Newman of NASA's Goddard Space Flight Center, Greenbelt, Maryland, Li adapted the Goddard Earth Observing System Chemistry-Climate Model (GEOS-CCM) to examine how climate change will affect ozone recovery.
The team inserted past measurements and future projections of ozone-depleting substances and greenhouse gases into the model.
Then, the model projected how ozone, the overall chemistry, and the dynamics of the stratosphere would change through the year 2100.
Though the concentration of chlorine and other ozone-depleting substances in the stratosphere will not return to pre-1980 levels until 2060, the ozone layer over middle latitudes is predicted to recover to pre-1980 levels by 2025.