Antarctic ozone hole – smaller this
year
1 October 2004
The ozone hole over Antarctica
appears to be about 20% smaller than last year’s record-breaking ozone hole.
Measurements by NIWA, supported
by Antarctica New Zealand, at Scott Base, Antarctica, are consistent with NASA
satellite data showing the area of the hole peaked at about 24 million square
kilometres, compared to 29 million square kilometres in 2003.
“Measurements from the ground
at Scott Base suggest that there is slightly more ozone this year than the
average for recent years,” says NIWA atmospheric scientist Dr Stephen Wood.
“But ozone levels are still lower than before the ozone hole started forming
in the early 1980s.”
“The first spring measurements
of ozone from Scott Base this year showed levels at around 200 Dobson Units (DU)
but have been as low as 165 DU in the past week. Satellite measurements are
reporting values as low as 110 DU in some parts of the hole. Before the early
1980s, ozone levels in Antarctica never went below 220 DU.”
The ozone hole is the result of a
combination of factors: man-made chemicals containing chlorine and bromine; the
isolation and cold of the Antarctic atmosphere during the polar winter; the
formation of polar stratospheric clouds; the chemical reactions that occur on
the surfaces of those clouds; and the return of sunlight in spring.
Although the man-made chemicals
that contribute to ozone depletion are already starting to decline in the
atmosphere (thanks to controls on their use under the Montreal Protocol), some
of the other factors vary from year to year. Because of this natural variation,
Dr Wood cautions against reading too much into the smaller size of the hole this
year. “We need to see smaller or less severe ozone holes over a number of
years before we can say for certain that ozone is recovering,” he says.
At present, the ozone-depleted
air is well contained over Antarctica. The only inhabited area it could affect
at the moment is the extreme tip of South America.
But Dr Wood says the hole will
indirectly affect New Zealand later in the year. “When the ozone hole breaks
up in November or early December, ozone-depleted air moves into surrounding
areas in the southern hemisphere, including New Zealand. The later the ozone
hole breaks up, the higher the sun is 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 skin-damaging UV levels can be extreme.”
Research conducted at NIWA’s
atmospheric research facility at Lauder, Central Otago, shows that approximately
half the long-term ozone decline at mid-latitudes in the southern hemisphere
(including New Zealand) has been caused by the export of ozone-depleted air from
Antarctica. In recent years, there has been about ten percent less ozone over
New Zealand in the summer than 30 years ago.
NIWA’s measurements of ozone
near Scott Base are part of research funded by the Foundation for Research
Science and Technology to understand what drives global change in the
atmosphere. The ground-based measurements are also important for validating
measurements taken from satellites.
For more information,
contact:
Dr Stephen Wood
NIWA Lauder, Central Otago
Tel: +64 3 440 0426
Dr Greg Bodeker
NIWA Lauder, Central Otago
Tel: +64 3 440 0438
National
Institute of Water & Atmospheric Research
New
Zealand’s leading provider of atmospheric and aquatic science
http://www.niwa.co.nz
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