Ozone recovery slows
The ozone layer is recovering, but not as fast as scientists had optimistically predicted in the past, the World Meteorological Organisation has said following a major report on progress made since the Montreal Protocol.Most stratospheric ozone is set to return to its undamaged pre-1980s state by 2049, according to the Scientific Assessment of Ozone Depletion: 2006 report produced by over 250 international experts, and published jointly by UNEP and the World Meteorological Organisation.
The last such assessment, dating back to 2002, had put the expected date for complete recovery five years earlier. What has changed since then, it seems, is that scientists have realised that estimates of how much ozone-depleting substances we are yet to pump out into the atmosphere had been over-optimistic.
The 1987 Montreal Protocol has been effective in cutting out the use of ozone-depleting substances - especially the CFCs used in refrigeration and air conditioning - with atmospheric concentrations of these substances now falling.
Despite these positive developments, it now turns out that scientists had underestimated the amount of CFC-11 and CFC-12 still present in fridges around the world, which will eventually make their way into the atmosphere and inevitably do their damage to ozone.
While the recovery date for most of the ozone has now been revised from 2044 to 2049, predictions for the Antarctic are worse still, with the recovery not expected until 2065 - 15 years later than once expected. Ozone depletion in the Antarctic is particularly severe, and the report's authors put the longer recovery time down to the "greater age of air in that region," which concentrates ozone-depleting substances and magnify the damage they cause.
"While these latest projections of ozone recovery are disappointing, the good news is that the level of ozone-depleting substances continues to decline from its 1992-94 peak in the troposphere and late 1990s peak in the stratosphere," said Michel Jarraud, secretary-general of WMO.
"Global changes in climate suggest that atmospheric conditions are different today from those prior to periods marked by ozone depletion. This may have implications for ozone recovery. Maintaining and improving observational and assessment capabilities are critical in separating effects due to changes in climate from those in ozone-depleting substances and will play a major role in verifying the effectiveness of actions taken under the 1985 Vienna Convention, the 1987 Montreal Protocol and its amendments."
"The early signs that the atmosphere is healing demonstrate that the Montreal Protocol is working. But the delayed recovery is a warning that we cannot take the ozone layer for granted and must maintain and accelerate our efforts to phase out harmful chemicals", said Achim Steiner, executive director of UNEP.
More information is available at the UNEP and WMO websites.