15 September, 2008

In May 1985 in the journal Nature British Antarctic Survey scientists reported their discovery of an ‘ozone hole’ over Antarctica. The United Nations Environmental Programme proclaims 16 September the International Day for the Preservation of the Ozone Layer, commemorating the date in 1987 on which the Montreal Protocol on Substances that Deplete the Ozone Layer was signed. All but three of the UN Member States have now ratified the Protocol. The Montreal Protocol gives the world an example of how to successfully control a global environmental problem.

The 2008 Ozone Hole

The 2008 hole is larger and deeper than the holes that formed when the discovery was made, and is virtually the same size as the 2007 ozone hole. However due to a stable atmospheric circulation this year, ozone depletion in 2008 got off to a slow start, and in August the hole was the smallest of the last decade. Since then it has grown very rapidly, and now covers some 24 million square kilometres, an area more than twice that of Europe.

The Antarctic ozone hole is caused by chlorine and bromine in the atmosphere, which come from CFCs and halons1. During the Antarctic winter, temperatures in the high atmosphere (the stratosphere), where most of the ozone is present, drop below -80°C and thin clouds form. Chemical reactions take place in the clouds and, when the sun returns in the spring, further reactions take place which destroy ozone. Typical ozone values for the Antarctic and the UK are around 300 Dobson Units2, but this drops to around 100 Dobson Units at the maximum of the ozone hole. When the ozone layer is thinnest much more ultra violet light can reach the surface.

Although the ozone hole mostly affects the Antarctic, it can pass over southern South America and the Falkland Islands. The increased ultra violet light reaching the surface poses a medical hazard and residents of the area without suitable protection face the prospect of rapid sunburn.

BAS scientists have measured ozone for over 50 years and we have the longest record of ozone measurements in the Antarctic. There was no ozone hole until the late 1970s. The hole begins to form in the Antarctic winter, and reaches its largest extent every September, before disappearing again by mid summer.

Jonathan Shanklin, is one of the original team who first reported the ‘ozone hole’ and is the head of BAS’s Meteorological and Ozone Monitoring Unit (MOMU).

He says

“The restrictions of the Montreal Protocol on the release of ozone depleting chemicals are working, but the Antarctic ozone hole is still likely to appear for many decades. If there had been no Montreal Protocol we would now be seeing widespread ozone depletion across the globe. Rather surprisingly the Montreal Protocol has also reduced global warming because there has been a real decline in CFCs and halons, which are very effective greenhouse gasses. It’s important that society continues to take action to reduce its damage to the atmosphere, otherwise we will bequeath future generations a significantly different world from that of today.”


  1. Chlorofluorocarbons (CFCs) were used in refrigeration and air conditioning systems, foam blowing for cavity wall insulation etc, in industrial solvents etc. Halons were used in fire extinguishing systems. Their release is controlled by the Montreal Protocol and its extensions and their amount in the atmosphere is decreasing.
  2. If all the ozone in a vertical column above the observer was brought down to sea-level it would form a layer just 3 millimetres thick. This corresponds to 300 Dobson units.
  3. Ozone observations at Halley and Rothera are carried out by members of the British Antarctic Survey’s Meteorological and Ozone Monitoring Unit (MOMU).

Press Office:
Linda Capper (British Antarctic Survey) 01223 221448 lmca@bas.ac.uk

UN Environment Programme