Saturday, October 21, 2006

Ozone troubles

Ozone holeThe ozone hole in the southern polar region, according to NASA and NOAA, has broken records for area and depth.

From September 21 to September 30, 2006, the average area of the ozone hole was the largest ever observed, at 10.6 million square miles. On September 24, the Antarctic ozone hole matched the single-day record of 11.4 million square miles, previously set on September 9, 2000.

On October 8, NASA's Aura satellite recorded another record: the most severe ozone hole observed to date, in the sense of the least amount of ozone. Aura observed a low value of 85 Dobson Units (a measure of ozone levels above a fixed point in the atmosphere) in a region over the East Antarctic ice sheet. This severe ozone hole (depicted in the graphic accompanying this post) resulted from the very high levels of ozone-depleting chlorine and from record cold conditions in the Antarctic stratosphere.

According to the NASA/NOAA report, international environmental law has played an ameliorative role, albeit a limited one, in remedying the problem. Thanks to the Montreal Protocol and its amendments, concentrations of ozone-depleting substances (mainly chlorine, bromine, and their precursors) in the troposphere peaked around 1995 and are decreasing in both the troposphere and stratosphere. These gases are believed to have reached peak levels in the Antarctica stratosphere in 2001.

But ozone-depleting substances typically have very long lifetimes in the atmosphere. They last more than 40 years. As a result, the ozone hole is expected to close very slowly -- perhaps by 0.1 to 0.2 percent for the next five to 10 years. These declines are dwarved by annual fluctuations in the Antarctic stratosphere.

According to the 2006 World Meteorological Organization/United Nations Environment Programme Scientific Assessment of Ozone Depletion, ozone hole recovery would be masked by annual variability for the near future. This assessment predicts full ozone hole recovery in approximately 2065.

Editor's note: This item has been posted simultaneously at Jurisdynamics and at BioLaw.


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