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Each spring the ozone layer over Antarctica nearly disappears,
forming a hole over the entire continent. The hole is created
by the interaction of some man-made chemicalsfreon, for examplewith
Antarcticas unique weather patterns and extremely cold temperatures.
Ozone in the stratosphere absorbs ultraviolet radiation from the sun,
thereby protecting living things. Since the ozone hole was discovered many
of the chemicals that destroy ozone have been banned, but they will remain in
the atmosphere for decades.
In 2000, the ozone hole grew quicker than usual and exceptionally large.
By the first week in September the hole was the largest ever11.4 million
square miles. The top image shows the average total column ozone values over
Antarctica for September 2000. (Total column ozone is the amount of ozone from
the ground to the top of the atmosphere. A relatively typical measurement of 300
Dobson Units is equivalent to a layer of ozone 0.12 inches thick on the
Earths surface. Levels below 220 Dobson Units are considered to be
significant ozone depletion.) The record-breaking hole is likely the result of
lower than average ozone levels during the Antarctic fall and winter, and exceptionally cold
temperatures. In October, however (bottom image), the hole shrank
dramatically, much more quickly than usual. By the end of October, the hole was
only one-third of its previous size. In a typical year, the ozone hole does not
collapse until the end of November. NASA scientists were surprised by this early shrinking
and speculate it is related to the regions weather.
Does a smaller hole mean that Antarctic ozone is recovering? Not yet, say NASA scientists. A deeper look at the ozone hole shows that for now weather still has a bigger influence on the size of the ozone hole than policies that limited emissions of ozone-destroying chemicals.