Ozone layer hole 'bigger than North America'

Sat 21 Oct 2006



THE hole in the ozone layer above Antarctica has grown to the biggest recorded size - larger than the North American continent - say NASA scientists, who yesterday released dramatic images documenting its changes.

The hole is a region where there is severe depletion of the layer of ozone - a form of oxygen - in the upper atmosphere that protects life by blocking ultraviolet rays from the sun. Scientists say made-man gases such as bromine and chlorine cause the hole by damaging the layer.

Paul Newman, atmospheric scientist at NASA's Goddard Space Flight Centre in Greenbelt, Maryland, said: "From September 21 to 30, the average area of the ozone hole was the largest ever observed, at 10.6 million square miles."

The increased size of the hole was blamed on unusual weather patterns. If the stratospheric weather conditions had been normal, the ozone hole would be expected to reach about 8.9 to 9.3 million square miles.

However, colder temperatures result in larger and deeper ozone holes, while warmer temperatures lead to smaller ones.

And this year, the lower stratosphere was about nine degrees Celsius cooler than average. In addition to the vast area covered by the hole, what ozone there is in the skies above Antarctica is thinner than usual this year.

The ozone hole is considered to be the area with total column ozone below
220 "Dobson Units". A reading of 100 Dobson Units means that if all the ozone in the air above a point were brought down to sea-level pressure and cooled to freezing, it would form a layer 1cm thick. A reading of 250 Dobson Units translates to a layer about 2.5cm thick (about an inch).

Satellite measurements observed a low reading of 85 Dobson units of ozone earlier this month. In July, by contrast, the ozone layer had a thickness of 300 Dobson units.

"These numbers mean the ozone is virtually gone in this layer of the atmosphere," said David Hofmann, the director of the global monitoring division at the US National Oceanic and Atmospheric Administration's Earth System Research Laboratory. "The depleted layer has an unusual vertical extent this year, so it appears the 2006 ozone hole will go down as a record-setter."

However, despite the dramatic size of the hole, the long-term prognosis for the ozone layer is healthy.

While there are and will continue to be year-to-year variations in the extent of its coverage, scientists expect a slow but complete recovery by the year 2065.

"I don't think there's a risk of the ozone hole growing and destroying the world," said Ken Caldeira, of the Carnegie Institution of Washington's department of global ecology.

Although CFCs and other dangerous gases that damage the ozone layer can linger in the atmosphere for as long as two generations, the amount of such damaging gases released into the atmosphere peaked in 1995 and has been declining ever since.

This means that, in theory, the ozone layer will have a chance to recover, although at an extremely slow and gradual pace for the next decade. Scientists expect the hole to reduce by just 0.1 to 0.2 per cent a year for the next ten years, before bouncing back more swiftly in later years. NASA also reported that ice was melting in Greenland more quickly than it was being replaced and more rapidly than scientists had believed.

"The results show a dramatic speed-up in the rate of ice-mass loss since the 1990s," said NASA researcher Jay Zwally. "A very large change in a very short time."

In a report published in Science magazine, researchers concluded that Greenland has lost 41 cubic miles of ice along its coast and gained only
14 miles from snowfall in its interior. Sea levels would rise 20ft if Greenland's icecap melted totally. Invisible barrier that protects planet from harmful solar rays

OZONE forms a protective layer high in the Earth's atmosphere, helping to reflect harmful rays from the sun.

Particles of ozone normally exist at levels of about 10 parts per million in a layer between nine to 30 miles above the ground.

However without this thin protective barrier virtually all forms of life from penguins to plants would be affected by ultraviolet radiation, which can cause skin cancer in humans and generally damages DNA, the fundamental building block of life.

Normally, there is a natural cycle of creation and destruction of ozone, a pale-blue gas with a pungent odour, but pollution can adversely effect this process. Warm temperatures on the ground tend to mean colder temperatures in the upper atmosphere, which exacerbates the problem.

Many of the ozone-damaging CFCs - once commonly used in refrigeration, air conditioning and industrial cleaning - were banned in 1985 by the Vienna Convention and in 1987 by the Montreal Protocol.

Related topic

* Climate change //news.scotsman.com/topics.cfm?tid=52

Informant: binstock


Ozone Hole, Double Record Breaker

NASA and National Oceanic and Atmospheric Administration (NOAA) scientists report this year's ozone hole in the polar region of the Southern Hemisphere has broken records for area and depth.



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