October 2007 Downloads & Links

Antarctic ozone update

The Secretariat of the World Meteorological Organization issues bulletins containing information on the state of the ozone layer in the Antarctic at roughly two-week intervals from August to November. The bulletins are based on data provided by WMO Members which operate ozone monitoring stations in the southern hemisphere and satellites to observe ozone globally.

Fourth WMO Antarctic Ozone Bulletin (18 October 2007)


The 2007 Antarctic ozone hole is relatively small, both in terms of ozone hole area (area where the total ozone column is less than 220 Dobson Units) and in amount of destroyed ozone (ozone mass deficit, i.e. the amount of ozone that would have to be added to the ozone hole in order to fill those regions where total ozone is less than 220 Dobson Units up to 220 Dobson Units).
From 1998 until now, only the ozone holes of 2002 and 2004 have been smaller than the 2007 ozone hole. It should be pointed out that this is not a sign of ozone recovery. The small ozone hole of 2007 is related to the mild temperatures of the Antarctic stratosphere during the 2007 winter. The stratosphere still contains more than enough chlorine and bromine to cause complete destruction of ozone in the 14-21 km altitude range. The amount of ozone depleting gases reached a maximum around year 2000 in the Antarctic stratosphere. This amount is now declining slowly at a rate of about 1% per year. One expects that the stratosphere will contain enough chlorine and bromine to cause severe ozone holes for another 1-2 decades. The severity of the ozone hole will, during this time period, to a large extent be determined by the meteorological conditions of the stratosphere during the Antarctic winter. Increasing amounts of greenhouse gases in the atmosphere will lead to lower temperatures in the stratosphere and this increases the risk of severe ozone holes during the next couple of decades. But there will always be interannual variability in the meteorological conditions, so one can also experience less severe ozone holes. The figures below show the ozone hole area, the ozone mass deficit, the average temperature over the 60-90°S region and the area where the temperature is low enough for the existence of polar stratospheric clouds.

ozoneThe ozone hole area reached a maximum of 25 million km2 in mid-September. In comparison, the ozone hole covered more than 29 million km2 in the record years of 2000 and 2006.

The ozone mass deficit reached 28 megatonnes (Mt) on 23 September. In comparison, it reached more than 40 Mt in the beginning of October 2006, which was a record year. Since 1998, only 2002 and 2004 experienced less severe ozone loss than 2007.



The situation with annually recurring Antarctic ozone holes is expected to continue as long as the stratosphere contains an excess of ozone depleting substances. As stated in the recently published Executive Summary of the 2006 edition of the WMO/UNEP Scientific Assessment of Ozone Depletion, severe Antarctic ozone holes are expected to form during the next couple of decades.

WMO and the scientific community will use ozone observations from the ground, from balloons and from satellites, together with meteorological data, to keep a close eye on the development during the coming weeks and months.

Fourth WMO Antarctic Ozone Bulletin (18 October 2007)



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