Stratospheric Ozone Depletion - The Changing Arctic Environment: The Arctic Messenger - page 106

2008 to 3.4 parts per billion (ppb) from its peak of 3.7 ppb. The rate of decline was lower
than anticipated probably because ofleakage ofCFCs from old equipment and from a more
rapid increase in use of HCFCs than expected, particularly in developing countries.
The 2010 WMO Ozone Report showed that declines in CFCs were responsible for
much of the decrease in total tropospheric chlorine over the previous few years. They are
now expected to decline throughout the present century. The decline of methyl chloroform
levels made a smaller contribution to the decrease in total chlorine than in earlier WMO as-
sessmentsbecauseithadalreadybeenlargelyremovedfromtheatmosphere.Brominefrom
halons stopped increasing in the troposphere during 2005-2008. Methyl bromide levels
continued to decline during the same period due to reductions in production, consumption
and emission. Some uses are not controlled by the Montreal Protocol.
These trends are very encouraging. You will remember that ozone-depleting sub-
stances gain access to the ozone layer by wafting up from their tropospheric reservoir.
There can be no doubt that the Montreal Protocol is working. However, the WMO 2010
assessment was not entirely good news. We have already noted that HCFC use has been
growing more quickly than expected and this is reflected in tropospheric levels. For ex-
ample,themostabundantHCFC(HCFC-22)increasedmorethan50%fasterbetween2007
and 2008 than between 2003 and 2004. Similarly, tropospheric abundances and emissions
of hydrofluorocarbons (HFCs; substitutes for CFCs and HCFCs) continue to increase, with
significant sources being from Europe, Asia and North America.
HFCs present a thorny regulatory problem. They do not erode the ozone layer, but
their growth in use is a direct result of their being chosen as an apparently benign re-
placement for the ozone-eating CFCs and HCFCs. However, they are not benign. They
are very potent greenhouse gases. We will learn more when we reach the “short-lived cli-
mate forcing” topic in the climate chapter. Attempts have been made to control them un-
der the Montreal Protocol, but so far, these attempts have been thwarted by those who feel
that such action should only be considered under the Framework Convention on Climate
Change. The present “action” arm of this agreement is the Kyoto Protocol, which has so
far been able to achieve very little.