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Antarctic ozone hole - near record levels

Measurements by NIWA staff at Scott Base, Antarctica, confirm reports of a large ozone hole this year.

“This year’s hole shaped up to be a whopper”, said NIWA scientist, Dr Stephen Wood, speaking from Scott Base. “It hasn't quite made it to the record size reached in 2000, but it has been very close to that mark.” NIWA calculations, which combine satellite information with ground-based measurements, show that the 2000 hole was over 30 million square kilometres. This year’s hole has been over 29 million square kilometres, but it is currently about 27 million square kilometres.

The area of the Antarctic ozone hole for 2003 compared to 2000, 2001, and 2002, calculated by using the NIWA assimilated total column ozone database. Also shown in grey shading is the range of values for the period 1978 to 2000.

“Early reports of this year’s ozone hole have highlighted two features, that the hole developed earlier than usual, and is very close to the record size”, he said.

Dr Wood said that the first ground-based measurements NIWA made there this spring were about 176 Dobson Units (DU), very close to the average of previous years, and certainly not the lowest there for this time of the year (which was 150 DU). At the centre of the hole satellite measurements have been reporting values as low as 105 DU. Ozone values over the Antarctic before the early 1980s were never less than 220DU.

Although last year’s Antarctic ozone hole was reduced in size and broke up earlier due to unusual meteorological conditions, it shouldn’t have been taken as a sign of recovery of the ozone hole problem.

“What this means is that although the man-made chemicals that contribute to the ozone depletion are already starting to decline in the atmosphere, we haven't yet seen a sustained reduction in the severity of the Antarctic ozone hole. There will always be variations from one year to the next, so before we can confirm the expected recovery, we would need to see smaller or less severe ozone holes over a number of years. Realistically, it might take another 10 years before we can be sure”, Dr Wood said.

At present the ozone depleted air is well contained over Antarctica and is not affecting New Zealand directly. In fact, the only inhabited area it could affect at the moment is the extreme tip of South America. However, there will be an effect later in the year when the ozone hole breaks up in November or early December, and ozone depleted air moves into surrounding areas in the southern hemisphere, including New Zealand. The longer the ozone hole lasts before breaking up, the closer it is to the time when the sun is highest in the sky over New Zealand and the larger the effect on UV levels. If New Zealand experiences a combination of lower ozone with high sun and few clouds, then UV levels can be extreme, but all three factors are important. Exposure to extreme UV can increase the incidence of skin cancer.

The NIWA measurements of ozone near Scott Base are part of a FRST funded research programme targeted at understanding what drives global change in the atmosphere. The ground-based measurements are also important for validating the measurements made by satellite-based instruments.

For further details, contact

Stephen Wood
Scott Base
phone +64 2 409 6700

or

Greg Bodeker
Lauder, Central Otago
phone +64 3 440 0438

http://www.niwa.co.nz