Many people have asked me whether global warming and the ozone hole are related. The short answer is "no". The long answer starts with "tangentially". Here's the scoop.
The ozone layer, found in the lower part of the stratosphere 9 to 20 miles up, prevents harmful ultraviolet radiation from reaching the Earth's surface. The depletion of the ozone (which is now recovering) was due to man-made chemicals like chlorofluorocarbons.
Global warming, in contrast, is what happens when high concentrations of greenhouse gases such as carbon dioxide (CO2) trap heat in the Earth's atmosphere. The increase in CO2 concentration is mainly due to the burning of fossil fuels and deforestation.
So they are separate problems, but there is one way they do interact. Greenhouse gases raise the temperature in the lower atmosphere, but decrease it in the upper atmosphere or stratosphere, where the ozone layer is.
I know that sounds counterintuitive – here's why it happens. Heat leaves the Earth by radiating into space, and CO2 is one of the radiators. With higher CO2 concentrations, the altitude at which the CO2 radiates to space increases. This causes more cooling in the stratosphere, and thus lower temperatures.
The cooling in the stratosphere leads to the creation of more ice crystals. Since reactions that destroy ozone occur on the surface of ice crystals, higher CO2 concentrations exacerbate ozone depletion. The role of ice crystals in ozone depletion is also why the problem is worse in cold places like Antarctica, where the ozone hole appears.
Year-to-year fluctuations make it hard to tell for sure, but the ozone layer appears to be mending, and the hole over Antarctica could be gone in a few decades. The recovery is thanks to an international treaty banning the use of chlorofluorocarbons – a hopeful reminder that nations can come together to solve global environmental problems.