Climate change is bringing mixed news to the ozone layer. Thanks to increasing CO2 concentrations and shifting air currents, the mid-northern hemisphere, including the United States, Canada, and Europe, will likely see its ozone restored ahead of schedule, according to a new study. Meanwhile, areas throughout the tropics and the mid-southern hemisphere, such as Australia, New Zealand, and Peru, may experience a delay in their ozone recovery.
Ozone is an important part of the upper atmosphere that protects both humans and ecosystems from harmful UV-B radiation. In the 1970s, the loss of ozone from the stratosphere (10 to 50 kilometers above Earth's surface) became a large concern: Scientists realized that ozone-depleting chemicals such as chlorofluorocarbons (CFCs), used in everything from aerosols to refrigerators, were destroying the ozone layer worldwide, especially at the poles.
Those aren't the only emissions that impact ozone, however. Researchers have long known that greenhouse gases might help the layer recover by cooling the stratosphere, which slows the rates of chemical reactions that destroy ozone. But climate change has another effect: It changes patterns of global air circulation. Until several years ago, no one had looked at how this would impact the ozone layer.
A team led by atmospheric scientist Darryn Waugh of Johns Hopkins University in Baltimore, Maryland, ran a chemistry climate model, which simulates atmospheric dynamics, energy transfer, and changes in chemistry over the next century. The results show that an increase in air flow through the mid-southern hemisphere will slow the rate of ozone production there, delaying ozone recovery in places such as Australia and Argentina. Even by the end of the century, the ozone layer in the tropics will not return to pre-1960s levels, the team reports this week in Geophysical Research Letters. Conversely, the United States and other places in the Northern Hemisphere will see enhanced ozone recovery, allowing them to return to mid-20th century ozone levels by about 2030. Ozone recovery at the poles will be minimally affected by climate change.
The findings point to an increased risk of skin cancer among fair-skinned populations in places such as Australia and New Zealand and high-altitude regions such as Peru and Chile, says atmospheric scientist Dan Lubin of the Scripps Institution of Oceanography in San Diego, California.
Atmospheric scientist Theodore Shepherd of University of Toronto in Canada, says that previous models have found similar regional trends but that this study provides a greater understanding of the individual effect of both climate change and CFC reduction on ozone recovery. And atmospheric scientist Martyn Chipperfield of the University of Leeds in the United Kingdom notes that although the patterns seen in this study are probably robust, other climate models may indicate different rates of ozone recovery.