What causes the ‘holes’?
The polar ozone holes are areas of lower concentration of stratospheric ozone that form over the Antarctic and the Arctic due to human activities. Ozone depleting substances containing chlorine and bromine atoms are released to the atmosphere through human activity, for example, through the use of aerosols and from refrigeration and air conditioning equipment. When these chemicals combine with certain weather conditions, particularly prolonged, extreme cold and strong winds that often occur in the stratosphere over the poles in Spring, chemical reactions cause ozone molecules in the stratosphere to be destroyed at a faster rate, leading to severe depletion of the ozone layer.
Antarctic ozone hole
What is it?
The Antarctic ozone hole is a thinning or depletion of ozone in the stratosphere over the Antarctic each spring. This damage occurs due to the presence of chlorine and bromine from ozone depleting substances in the stratosphere and the specific meteorological conditions over the Antarctic. The Antarctic is much colder than the rest of the planet and experiences consistent strong winds.
The Antarctic ozone hole develops in August and dissipates in late November when warmer weather and ozone rich air from outside the polar vortex disrupts the chemical reactions causing ozone depletion.
What has happened so far?
Abnormally low ozone concentrations in the stratosphere above the Antarctic were first reported by British scientists in 1985.
The Antarctic ozone holes in 2000 and 2006 were the largest on record, measuring around 29.8 and 29.6 million square kilometres respectively (more than three and a half times the size of Australia). At times they extended over populated areas in Chile, South America.
With the decrease in ozone depleting chemicals in the atmosphere, Antarctic ozone holes in recent years have not been as large or as deep as these earlier holes. However, a very cold, stable stratosphere could still lead to a large amount of ozone depletion in future years. One way the stratosphere might cool significantly is through the continued build up of carbon dioxide (CO2) and other greenhouse gases, along with synthetic greenhouse gases, in the atmosphere.
More information about the Antarctic ozone hole
Antarctic ozone hole summary reports
Issued by CSIRO each year when the Antarctic hole forms in the Southern Hemisphere spring.
Total Ozone Mapping Spectrometer (TOMS) satellite data 1997-2017
The data are the October 1-15 averages of the total column ozone amount, given in Dobson Units (DU). The area extent of the ozone hole for each year is indicated by the red 220 DU line.
2017 ozone hole daily data
Arctic ozone hole
What is it?
The Arctic ozone hole is a thinning of ozone in the stratosphere over the Arctic during spring.
Why wasn’t it discovered at the same time as the Antarctic ozone hole?
Generally the weather in the Arctic is not as cold as in the Antarctic. Extreme, prolonged cold weather and strong winds are one of the major contributors to the large size of the Antarctic ozone hole.
In 2011 scientists noticed the amount of ozone in the Arctic stratosphere declined to levels low enough to be described as an ozone hole. This was linked to persistently cold temperatures and circling winds, known as the Arctic vortex, which prevented cold air from escaping the region.
Prospects for the long-term recovery of the ozone layer are good. It is anticipated that the recovery of the ozone layer will gradually diminish the large ozone holes that occur over both the Antarctic and Arctic.
Through the Montreal Protocol on Substances that Deplete the Ozone Layer (the Montreal Protocol) production and imports of major ozone depleting substances ceased for developed countries in 1996, and for developing countries in 2010.
Scientists predict that if the international community continues to meet their Montreal Protocol obligations, the ozone layer should recover to pre-1980 levels over the mid-latitudes by 2050 and over the Antarctic by 2065.