The Antarctic ozone hole has set a new record. It has lasted longer than in any other year - for nearly 100 days.

The World Meteorological Organisation, a UN agency, says the hole measured 13 million sq km for most of November.

The WMO says this is the first time since tracking of ozone levels began in the 1970s that the hole has measured more than 10 m sq km for so long.

Between 65 and 90 degrees south, the WMO says, the average ozone level was the lowest ever recorded for November.

Some good news

Overall, south of 60 degrees latitude, the ozone destruction was about 30% worse than the average for the last eight years.

The good news is that the hole in November was barely half the size it had been in September.

It then measured a record 25 m sq km, two and a half times the size of Europe.

At the end of September, according to the WMO, ozone depletion was the greatest ever observed for the time of year, and it covered a larger area than ever before.

The previous record hole, in 1993, measured 22 m sq km. The average over the past few years has been about 20 m sq km.

High loss of ozone in November

The WMO says average ozone levels over the entire south polar area during September were about 45-50% below normal.

But at higher levels, between 14 and 22 km above the earth, ozone loss was 80-95%

The ozone layer protects all life against the harmful effects of the sun's ultra-violet radiation, which can cause blindness and cancer.

New level of damage

While humans can take some precautions against exposure, there is little to be done for animal or plant life short of stopping the damage to the ozone layer.

UV radiation is known to damage plankton, the microscopic organisms which are at the base of the marine food chain.

All terrestrial life at risk

Scientists at the University of Plymouth have reported that the reproductive cells of plankton appear to be several times more sensitive to UV radiation than mature cells.

They say that 'the ecological significance of elevated UV(B) exposure in the marine environment may be seriously underestimated'.

Trouble in store

The ozone is being destroyed mainly by chlorofluorocarbons (CFCs), gases which used to be widely used in refrigeration and aerosols.

Their use is now banned in developed countries, but the developing world has until 2005 to phase them out.

Because they are so long-lived at high altitudes, CFCs emitted years ago will go on causing damage for a long time to come.

There is even a thriving black market trade in smuggling contraband CFCs across frontiers.

Other ozone depleters include halons, used in firefighting, and the fumigant methyl bromide.

An international agreement on protecting the ozone layer, the Montreal Protocol, was signed in 1987.

The WMO says there are signs that the protocol is beginning to have an effect. But it will take at least until the middle of the next century before the ozone has returned to normal.

Scientists expect things to go on getting worse for some years yet before they start to improve.