The ACIA reckons that in recent decades average temperatures have increased almost twice as
fast in the Arctic as they have in the rest of the world. Skeptics argue that there are places,
such as the high latitudes of the Greenland ice sheet and some buoys at sea,
where temperatures seem to have fallen. On the other hand, there are also places,
such as parts of Alaska, where they have risen far faster than average. Robin Bell,
a geophysicist at Columbia University who was not involved in the report’s compilation,
believes that such conflicting local trends point to the value of the international,
interdisciplinary approach of this week’s report. As he observes, “climate change,
like the weather, can be patchy and you can get fooled unless you look at the whole picture.”
And there is other evidence of warming to bolster the ACIA’s case. For example,
the report documents the widespread melting of glaciers and of sea ice,
a trend already making life miserable for the polar bears and seals that depend on that ice.
It also notes a shortening of the snow season. The most worrying finding, however,
is the evidence — still preliminary — that the Greenland ice sheet may
be melting faster than previously thought.
That points to one reason the world should pay attention to this week’s report.
Like a canary in a coal mine, the hypersensitive Polar Regions may well experience
the full force of global warming before the rest of the planet does. However,
there is a second and bigger reason to pay attention. An unexpectedly rapid warming
of the Arctic could also lead directly to greater climate change elsewhere on the planet.
Arctic warming may influence the global climate in several ways.
One is that huge amounts of methane, a particularly potent greenhouse gas,
are stored in the permafrost of the tundra. Although a thaw would allow forests
to invade the tundra, which would tend to ameliorate any global warming that is
going on (since trees capture carbon dioxide, the greenhouse gas most talked about in
the context of climate change), a melting of the permafrost might also lead to a lot
of trapped methane being released into the atmosphere,
more than offsetting the cooling effects of the new forests.