Climate Change in the Arctic - The Changing Arctic Environment: The Arctic Messenger - page 293

ozone is attacked by solar radiation, so at this time, its concentrations in the troposphere
decline.
It follows that the heat-trapping effect of the ozone is greatest in the spring and that
most of the ozone's contributions to the greenhouse effect occur within 45° latitude from
the equator. Nevertheless, it is estimated that the seasonally averaged temperature response
attributable to the ozone for 60-90° N is 0.43°C.
Methane is a GHG with an atmospheric lifetime of about 12 years and can therefore
also be thought of as a SLCF. It is actually a much more potent GHG with a GWP relative
to CO 2 of 21 but is present in the atmosphere at much lower concentrations. The other
SLCFswehavestudiedsofarhavesuchshortresidencetimesintheatmospherethatdiffer-
ences in source strength have major implications on impacts. However, methane remains in
the atmosphere for about 12 years, which enables it to be globally well mixed throughout
the atmosphere. Therefore, its impact on global warming has no strong regional signals (as
distinct, for example, to BC). Since the Industrial Revolution, atmospheric concentrations
have roughly doubled and have now reached about 1,770 ppb (parts per billion). Ice core
measurements indicate that this is higher than at any time in at least the last 650,000 years.
It is estimated that the seasonally averaged temperature response attributable to methane
today for 60-90° N is about 0.34°C.
Anthropogenic activities, such as coal and gas production, animal and other waste dis-
posal, biomass burning, rice production and enteric fermentation from animal husbandry,
account for about two-thirds of methane emissions. They are expected to rise in the fu-
ture in consort with the increasing intensity of industrial and economic activity. However,
the single largest source is believed to be natural wetlands. The wetlands north of 60° N
alone may contribute about 13% (although there is much uncertainty with these estimates).
Measurements over the last decade have suggested that northern wetland emissions are in-
creasing as temperatures warm, soils become wetter and permafrost thaws - often being
replaced by thermokast lakes, through which bubbles of methane can be seen coming to
the surface. The ultimate source of this Arctic methane is biological degradation of organic