Geology Reference
In-Depth Information
dioxide emissions. To add insult to injury, the melting of the Greenland ice cap would
send enough fresh water into the sea to flip the oceanic thermohaline circulation into
its 'off' mode very quickly indeed, perhaps triggering changes to the climate of western
Europe and possibly beyond.
But it is not just Greenland that is melting—so is the vast majority of Gaia's realm
of ice and snow. As the great melt proceeds, Gaia experiences positive feedbacks on
warming. In the last 30 years, the extent of snow cover in the far northern hemisphere
during spring and summer has decreased by 30%, and even though there was a slight
increase in winter snow cover in North America, the albedo decrease of the exposed
bare ground in the warmer months has made a net contribution to the overall warming
of the region and the planet. The disappearance of sea ice in the Arctic has encouraged
explorers to look for a navigable route through the long sought-after Northwest Passage
between Greenland and Canada. Polar bears are threatened with extinction, for they will
no longer have vast expanses of sea ice over which to roam in their hunt for seal. Cari-
bou, moose and polar bear—the future for these animals looks bleak as their domains
become increasingly blocked by expanses of open water or thin ice.
The realm of ice and snow is also under siege in Antarctica, where dramatic changes
are taking place as the continent warms at a rate of about 0.5°C per decade. The 31st
January 2002 is a date to remember, for on that day large sections of the Larsen B ice
shelf began to break away from the main mass of the icy continent. Huge amounts of
ice were involved— 32,500 square kilometres, an area bigger than Rhode Island weigh-
ing in at around 720,000 million tonnes, broke away in a 30-day period, littering the
surrounding ocean with icebergs of all sizes. This is an unusual event. Recent eviden-
ce shows that Larsen B has been stable for the last 10,000 years, so its demise can be
linked with some confidence to our warming of the climate. Ice shelves sit on the ocean
and snuggle right up against Antarctica like whale calves alongside their mothers, so the
collapse of an ice shelf doesn't by itself lead to an increase in sea level. Ice shelves are
made of ice sliding down into the sea from glaciers on the continent, and seem to act like
'corks in a bottle', preventing the glaciers behind them from plunging catastrophically
into the ocean. Remove the corks, and the 'unstopped' glaciers surge into the sea, un-
leashing dramatic rises in global sea level as their huge bulk adds to the overall volume
of the world's ocean. There is a real danger that the Ross ice shelf could soon begin to
collapse. This ice shelf is the size of France, with 200-metre-high cliffs at its seaward
end, and a maximum depth of one kilometre. Its break-up would cause so much ice to
reach the sea from the West Antarctic ice sheet that global sea levels would increase
by 5-7 metres. Indeed, the melting of the entire Antarctic ice sheet would raise glob-
al sea levels by as much as a phenomenal 50 metres. These and other changes to the
distribution of ice shelves are playing havoc with Antarctic wildlife. Penguins are suf-
