It is 25 years since the world took urgent action to slow the catastrophic decline of ozone in the earth’s atmosphere with the signing of the Montreal Protocol.

The international agreement banned the production and release of man-made substances, such as chlorofluorocarbons (CFCs), which were destroying the protective blanket of ozone in the stratosphere (10–50 kilometres above Earth’s surface).

Australian Antarctic Division atmospheric scientist Dr Andrew Klekociuk said ozone is vital to life on earth as it absorbs harmful ultraviolet radiation and influences climatic conditions.

“Without the Montreal Protocol the planet today would be a very different place; in the mid-latitudes under the most extreme conditions, human skin would burn within 5 minutes of being exposed to the sun,” Dr Klekociuk said.

The ozone hole was first detected over Antarctica when British scientists compared the amount of ozone found in the early 1980s with earlier measurements which dated back to 1956.

“The ozone hole forms each year when there is a sharp decline, currently up to 60%, in the total ozone over most of Antarctica for a period of about two months during September and October.

“The most recent figures for the 2011 Antarctic ozone hole show it was relatively large, at 25.7 million square kilometres in area, and by this measure, the 11 largest of the 32 holes assessed since 1979.”

“There are signs that ozone recovery has commenced but a clear decrease in the size of the Antarctic Ozone Hole is not expected to be noticeable until between 2012 and 2020, with recovery to pre-ozone hole levels between 2050 and 2070,” Dr Klekociuk said.

The Australian Antarctic Division and research partners recently commenced a new assessment of the effects of ozone depletion and recovery on climate in the Southern Hemisphere.

The work involves improving the capabilities of the Australian ACCESS climate model to simulate atmospheric chemical processes in greater detail.

The research is aimed at helping to assess trends in temperatures and ozone concentrations in the stratosphere, and how these trends will interact with climate change at the Earth’s surface.