ENVIRONMENT: The ozone hole that forms each September over the Antarctic has reached its biggest extent for this year, equalling but not surpassing the worst on record.
The hole, which has human health and environmental implications, lay for a time over the southern tip of South America.
Scientists on the ground and satellites overhead each year watch as ozone in the upper atmosphere begins to disappear when the Antarctic spring approaches. Man-made chlorine and bromine-based chemicals released into the atmosphere over decades react with sunlight and super-cooled polar air to destroy ozone. The gas is essential for life on earth as it helps to block ultraviolet radiation coming from the sun. Too much UV radiation can increase the risk of skin cancers, cataracts and disturb normal plant growth.
This year's hole peaked in size at about 28 million square km according to the British Antarctic Survey, covering a space roughly equal to the North American continent. Its huge expanse, close in size to the 2000 hole, is noteworthy but also the fact that it formed earlier and faster than usual, the survey added. The hole at 20 million square km was much smaller last year, but this didn't mean things were getting worse according to the US National Aeronautics and Space Administration. Ozone destruction depends on the presence of very cold air circulating over Antarctica and the formation of ice crystals which support the chlorine reaction.
Concentrations of these chemicals have been in decline since 1994 and are about 6 per cent down from their peak. Satellites show that although the rate of decline in ozone in the upper stratosphere is slowing, the total ozone amount is still declining. It will take at least a decade to know whether the decline has halted.
