Stratospheric Ozone Depletion - The Changing Arctic Environment: The Arctic Messenger - page 101

in Canada, Norway and Sweden. However, other uses of CFCs remained unregulated, and
after a brief falloff, their global production began to rapidly grow in the early 1980s.
The next stage in this story began in 1985, when Joseph Farman and colleagues pub-
lished what is now a classic paper. They had discovered the Antarctic ozone hole. Since the
late1950s,FarmanhadbeenmeasuringstratosphericozoneaboveHalleyBayinAntarctica
(76° S and 27° W) using a ground-based instrument. In 1982, he noticed a massive spring-
time ozone reduction of about 40% in comparison with data from the 1960s. He knew that
NASA satellites had not reported this apparent anomaly and he assumed he had an instru-
ment problem. However, a new instrument in the following spring detected another sharp
drop in ozone levels. When he looked at his old records, he found that the spring anomaly
had been occurring since the mid-1970s, and even before then, a more modest decline had
beentakingplace. Afteranotherinstrument located ontheArgentine Islands(65°Sand64°
W) to the north-west also detected the steep decline, Farman and his colleagues published
their paper in the journal Nature .
NASA quickly found that its satellite-borne instruments had been detecting the ozone
decline, but its computerized data analytical programme contained cutoff values to remove
any data that did not appear to be credible. This is a common feature for modern instru-
mentation that is capable of deluging scientists with too much information, but on this oc-
casion, the baby had been thrown out with the bathwater. Once NASA corrected its ana-
lyses and the Nimbus-7 satellite survey was published, the world was in for a shock. The
corrected satellite data revealed a springtime Antarctic “hole” in the stratospheric ozone
layer.ItwassolargethatitcoveredageographicalarealargerthanthatoftheUnitedStates.
We now know that during the two to three months of the Antarctic spring/early summer,
about 50% of the total amount of ozone in the stratosphere vanishes. Over the two decades
following the publication of Farman's paper, the spring Antarctic ozone hole grew by up to
27 million square kilometres.
It is time for another quick digression. If you are tempted to do more reading about
ozone depletion, you will quickly encounter Dobson units which are used to measure the
total amount of ozone in the atmosphere above a point on Earth's surface. One Dobson unit