SCIY.Org Archives

This is an archived material originally posted on sciy.org which is no longer active. The title, content, author, date of posting shown below, all are as per the sciy.org records
Largest Antartica ozone hole yet recorded, despite cuts in CFCs

Originally posted on sciy.org by Ron Anastasia on Fri 20 Oct 2006 01:11 PM PDT  

The Australian - The Nation

Record ozone hole despite cuts in CFCs
October 21, 2006
20oct-ozone

Source: NASA

THE hole in the ozone layer over the southern hemisphere is the largest ever, covering an area more than three times the size of Australia.

During the last nine days of September, the hole in the ozone layer covered, on average, nearly 17.5 million square kilometres.

The expansion to a size greater than the surface area of North America has been observed in recent weeks by American and Australian scientists.

"We now have the largest ozone hole on record," said Craig Long of the US National Oceanic and Atmospheric Administration (NOAA). The ozone layer girdles the Earth in the upper atmosphere, or stratosphere. It protects plants, animals and people by blocking harmful ultraviolet rays from the sun.

Ozone depletion is caused by the effects of stratospheric chlorine and bromine. The gases are released in summer when sunlight acts on artificial compounds like chlorofluorocarbons, once used as coolants and fire retardants.

The record-breaking hole was announced yesterday by the US space agency, NASA, and NOAA. Scientists at the CSIRO identified the hole last week, said atmospheric scientist Paul Fraser.

"We were looking at data on the NASA site and noticed the hole looked likely to be the biggest ever," Dr Fraser said.

The data was recorded by the Ozone Monitoring Instrument aboard NASA's Aura satellite. The instrument detected record low levels of ozone over the East Antarctic ice sheet.

Balloon-borne instruments operated by NOAA made further measurements directly over the South Pole. Ozone levels had plunged from 300 Doppler Units (DU) - a measure of ozone between 13 and 20km above Earth - to 93DU.

"These numbers mean the ozone is virtually gone in this layer of the atmosphere," said David Hofmann, director of NOAA's Global Monitoring Division. "The depleted layer has an unusual vertical extent this year, so it appears that the 2006 ozone hole will go down as a record-setter."

While the size of the hole is alarming, it does not mean that increased amounts of ozone-depleting chemicals are reaching the atmosphere, said Paul Lehmann with the Bureau of Meteorology Research Centre in Melbourne. "There is mounting evidence that the ozone is slowly recovering," he said.

"The (yearly) size of the hole is due to the effect of atmospheric influences like wind and temperature." Dr Fraser noted that these conditions differed from year to year, effectively "masking" the decline in ozone-depleting substances and the increase in protective ozone.

"There are less ozone-depleting chemicals but they are more effective (when it's cold)," Dr Fraser said. "This is the coldest year ever." Also, chlorine and bromine remain in the stratosphere for about 50 years.

Signatories to the 1975 Montreal Protocol and its amendments, including Australia, agreed to phase out ozone-depleting substances.

Its estimated levels of the destructive gases peaked above Antarctica in 2001 and are now declining.


- end -

Attachment: