Still need to be alert for ozone layer hole

'The recovery of the ozone layer in Antarctica cannot be taken for granted and requires constant vigilance . ' It was a message from Dr. Jonathan Shanklin, one of the first scientists to recognize the annual thinning of the Earth's shield in the 1980s.

The "gap" in the stratosphere above the 'white continent' was recorded to be the smallest in three decades.

'It is welcome,' Dr. Shanklin said, but we should really only see it as an anomaly.

The expected-than-expected recovery of ozone levels is thought to be due to stormy conditions above the atmosphere causing the Earth to warm up. This has prevented chemical reactions and retained the chlorine and brom atoms that often destroy the ozone layer 15-30km from the planet.

Will the ozone layer (dark blue) be fully narrowed in the next few weeks?

"To know whether international treaties are effective, we need a long-term review , " Dr. Shanklin said. "A quick glance this year might make you think that countries have intervened to improve the ozone hole. But they haven't. And although things are improving, there are still a number of countries that are produce chlorofluorocarbons (CFC) , the chemicals that cause problems. We cannot be complacent. "

Dr. Shanklin, along with Joe Farman and Brian Gardiner, first warned the world in 1985 that ozone concentrations were plummeting in the Antarctic sky every spring. Their research contributed to the formation of the Montreal Protocol, an international agreement to control chlorofluorocarbon (CFC) gas worldwide. This international treaty removes most chlorine and bromine related chemicals associated with ozone depletion. At the time, these substances were widely used as refrigerants, detergents and as propellants in experimental aerosols.

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