Stratospheric Ozone Depletion - The Changing Arctic Environment: The Arctic Messenger - page 108

Projected Recovery of the Stratospheric Ozone Layer
In the mid-1990s, global average stratospheric ozone levels stabilized, but they have not yet
shown any substantial increase. Here is the situation from data analyses available from the
WMO in 2010. For the period 2006-2009, the average ozone values were:
Latitude 90° N to 90° S: 3.5% below 1964-1980 averages
Latitude 60° N to 60° S: 2.5% below 1964-1980 averages
For the same period but using a different method of recording, the average mean total ozone
values were:
Latitude 35° N to 60° N: 3.5% below 1964-1980 averages
Latitude 35° S to 60° S: 6.0% below 1964-1980 averages
Therefore, substantial ozone depletion affects almost all of Europe, Russia, Australia, New
Zealand and North America and a part of South Africa and South America. However, smal-
ler decreases in stratospheric ozone have been observed in mid-latitude regions of the world
and no statistically significant depletion has been detected over the tropics. Where I live in
southern Canada, the ozone layer has thinned by an average of about 7% since the 1980s.
In the Antarctic, the ozone hole continues to appear every year between late August
and early October.Inspring 2000,it reached a record geographical extent byoccupying 28.3
million square kilometres. At this time of year, some vertical profiles from stations located
near the South Pole show almost complete ozone destruction in the lower stratosphere.
In the Arctic, ozone depletions have also been seen over the last 20 years. However,
the Arctic stratosphere is usually not cold enough for a sufficiently long time to allow the
widespread formation of polar stratospheric clouds that are essential for the dramatic nature
of seasonal ozone depletion above the Antarctic. This is because the high altitude winds that
circle the Arctic (the polar vortex) and which trap cold air over the North Pole are not as ef-
fective at doing so as their counterparts in Antarctica. Consequently, in the 1998 AMAP as-