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Extreme contrast in ozone losses at Poles

india Updated: Dec 29, 2006 14:16 IST

A study released on Monday shows just how dramatic the ozone loss in the Antarctic has been over the past 20 years compared to the same in the Arctic.

The study found ‘massive’ and ‘widespread’ localised ozone depletion in the heart of Antarctica’s ozone hole region, beginning in the late 1970s, but becoming more pronounced in the 1980s and 90s.

The US government scientists who conducted the study said that there was an almost complete absence of ozone in certain atmospheric air samples taken after 1980, compared to earlier decades.

In contrast, the ozone losses in the Arctic were sporadic, and even the greatest losses did not begin to approach the regular losses in the northern hemisphere, the researchers said. “Typically the Arctic loss is dramatically less than the Antarctic loss,” said Robert Portmann, an atmospheric scientist with the National Oceanic and Atmospheric Administration in Boulder, Colorado.

Scientists have been tracking the expanding ozone hole over Antarctica for some 20 years now. In October, NASA scientists reported that this year’s hole is the biggest ever, stretching over nearly 11 million square miles.

In Antarctica, local ozone depletion at some altitudes frequently exceeded 90 per cent, and often reached up to 99 per cent during the Antarctic winter in the period after 1980 compared to earlier decades, the researchers said.

In the Arctic, the losses occasionally peaked at 70 per cent, and some losses of 50 per cent were seen in the mid 1990s, when temperatures were particularly low, but the scale and scope of the problem was much less than what was seen in the Northern Hemisphere.

Recent studies have also pointed to large ozone losses in the Southern Hemisphere, but the NOAA researchers said their study showed that these events were rare and did not appear to signal a trend.

“We saw small to moderate ozone losses in the very coldest winters, when the stratospheric conditions are ripe for ozone loss, but they were rarer than we expected,” said Portmann.