The ozone layer that protects people from the sun’s ultraviolet radiation is not recovering over most highly populated regions, scientists warned on Tuesday.
The greatest losses in ozone occurred over Antarctica but the hole there has been closing since the chemicals causing the problem were banned by the Montreal protocol. But the ozone layer wraps the entire Earth and new research has revealed it is thinning in the lower stratosphere over the non-polar areas.
Reduced protection from cancer-causing UV rays is especially concerning towards the equator, where sunlight is stronger and billions of people live. The reason for the falling ozone at lower latitudes is not known, though scientists suspect a chemical used in paint stripper and a change in atmospheric circulation caused by climate change.
The cause of the decline is unknown but might be the result of global warming. Ozone is produced by chemical reactions in the atmosphere over the tropics and then distributed towards the poles world by large air circulation currents. But warming trends could be strengthening these currents, moving more ozone to the poles and leaving less at lower latitudes.
Another suspect is so-called “very short lived substances” (VSLS) – industrial chemicals that destroy ozone. It was thought they broke down too quickly to reach the stratosphere, but that may need to be re-examined.