Gradual decline in chemicals that diminish the ozone

This can last up to three months, when conditions change and the ozone hole closes.

In recent years, there has been a gradual decline in chemicals that diminish the ozone. The 1987 Montreal Protocol, which led to the elimination of harmful chemicals in refrigeration and aerosol spray cans, has played a major part in this. Even so, if could be decades before the damaging chemicals are dispersed from the atmosphere.

Sophisticated computer predictions show the ozone could recover by 2050, although the Antarctic hole may not be repaired for another 20 years, show figures from the 2010 Quadrennial Ozone Assessment, published by the World Meteorological Organization and United Nations Environment Programme, with input from NASA and the NOAA.