THE PLANETARY COLLAPSE

SCIENCE > THE PLANETARY COLLAPSE >The great planetary collapse

Up north, the pack ice is melting. Polar bears are threatened and the disappearance
of the ice in summer could modify climates and life styles in considerable
proportion.

Global warming ? “The American submarines were those who revealed to us the scope of the problem”. For Christian de Marliave, who has twenty years of experience in the poles and who is the scientific coordinator of the Tara Arctic project, as for the entire scientific community, it was a great surprise. Indeed, partially demobilized at the end of the cold war, the American Navy lent its nuclear submarines to the scientists to visit the pack ice from below.

Between 1995 and 1999, 100 000 nautical miles were thus covered and the sonar gave their verdict without appeal : the melt down is breath taking! “On satellite photos, we notice that the polar ice surface has diminished by an average
of 8 to 10% in the past thirty years. But the pack ice has reduced by 40% in thickness during the same period which is considerable” adds Christian de
Marliave.
Mathematical models produce converging evaluations. “The five extrapolations that were calculated all show about the same thing : there will be no more summer pack ice within the next twenty to fifty years” asserts Jean-Claude Gascard, research director at the oceanographic and climatology laboratory of the Pierre and Marie
Curie University in Paris and coordinator of the Damocles programme which is leading scientific studies from the Tara schooner.
The first species to suffer from this disappearance will undoubtedly be the polar
bear. “The bear hibernates in the winter and stores fat in the summer” continues Jean-Claude Gascard. “If there is no more summer pack ice he is sentenced to disappear”. Christian de Marliave adds “The bear feeds on seals that he catches when
they emerge from the ice. Without the pack ice, he is finished. He is a good swimmer but has no chance to catch up with a seal in open water”. Three cases of cannibalism have been witnessed among polar bears this year : a possible prelude of what is to
come with the increased scarcity of their food.

“Mathematical models are imperfect and the worse is not necessarily what is in store” moderates however Jean-Claude Gascard, “studies that we are carrying out on Tara’s board will enable us to improve these models”. Instead of submarines, the
Damocles researchers are going to install floats under the ice, which will drift 50 m deep in the heart of a 1 000 km diameter circle. Each one will be equipped with an inversed sonar and will measure the thickness of the pack ice for
the next two years.

However, the pack ice melt down will have nearly no effect on ocean levels. Greenland, on the other hand, is a fantastic fresh water reservoir. The ice that covers it is the outcome of thousands of years of precipitations. It is a
thick mass of maybe more than 3 km that is loosing more than a hundred billion tons of ice per year according to the satellite observations of the Grace2 programme. Not only because of the melt down but also because of the accelerating ice slide of glaciers in the sea, a kind of collateral damage due to the warming.

The Kangerdlugssuaq glacier hurtles down the Greenland coast at the mind boggling speed of 14 km per year. If all of Greenland began to melt, the average ocean levels would rise seven meters : London or New York would be
underwater not to mention Venice!
“It is a catastrophic scenario that is not going to take place soon… However, even if Greenland reduced its ice by only 10%, the sea level would rise by 70 cm. Which is already quite something” points out Jean-Claude Gascard. Moreover the
melting of this freshwater ice risks modifying the thermohaline (movement of the expanses of water according to temperature and salinity) and thus the “north Atlantic drift”.
This ocean current, stemming from the Gulf Stream, heats up Western Europe and
Scandinavia. It allows for human life with appreciable comfort conditions. But the
rerouting of the drift, its’ slowing down, or perhaps even its full stop would entail a drastic cooling off of the Scandinavian coasts and even
a possible glaciation.

A glaciation caused by global warming ? As paradoxical as it may appear, the scenario is not new. It already happened. Between 9 000 and 8 500 BC, in full post-glacier debacle, the melting of the North American glaciers had
made the drifts’ regimen drop. It resulted in a re-glaciation of the Scandinavian peninsulas during some 500 years.

1 : Steven C. Amstrup et al, Polar Biology, Online first, 27 April 2006
2 : Scott B. Luthcke et al, Science, 20 October 2006

Eric Biegala

Tara 2006-2007

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