23 August, 2006

British Antarctic Survey scientists first announced the discovery of the hole in the ozone layer above Antarctica 21 years ago. Published by Joe Farman, Brian Gardiner and Jonathan Shanklin in the journal Nature in May 1985, the findings provided an early warning of the dangerous thinning of the ozone layer worldwide and paved the way for the Montreal Protocol.

BAS scientists carry out ozone observations at Halley and Rothera Research Stations, and ozone has been monitored at BAS research stations for nearly 50 years – the longest record of ozone measurements in the Antarctic.

The amount of ozone overhead should follow a regular seasonal pattern. This is what occurred during the first 20 years of BAS measurements, but by the late 1970s clear deviations were observed. In every successive spring the ozone layer was weaker than before, and by 1984 it was clear that the Antarctic stratosphere was progressively changing.

The Antarctic ozone hole is caused by chlorine and bromine in the atmosphere, which come from chlorofluorocarbons (CFCs) and halons. The hole itself begins to form when sunlight returns at the end of the Antarctic winter, and reaches its largest extent every September, before disappearing again by mid summer. During the Antarctic winter, temperatures in the high atmosphere (the stratosphere), where most of the ozone is present, drop below -80°C and high altitude clouds form. Chemical reactions take place in the clouds and, when the sun returns in the spring, further reactions take place which destroy ozone. When the ozone layer is thinnest much more ultra violet light can reach the surface.

CFCs were used in refrigeration and air conditioning systems, fire control and industrial solvents. Under the 1987 Montreal Protocol and its amendments, the production and consumption of CFCs, halons, carbon tetrachloride and methyl chloroform were phased out. Scientists at BAS believe that the hole in the ozone layer will be repaired by 2100.