Evidence of ice loss from both poles this week has sparked fresh fears that global warming is progressing faster than scientists had predicted.
Arctic ice has thinned dramatically, as well as shrinking in area, according to US research. Thin seasonal ice, which melts and refreezes each year, now makes up about 70 per cent of the Arctic winter ice, up from about 40 to 50 per cent in the 1980s and 1990s, leaving far less of the older, thicker ice that is harder to melt.
In the Antarctic, an ice bridge connecting an island to the Wilkins ice shelf – a sheet of ice about the size of Northern Ireland – shattered as scientists monitored it through satellite observations.
“What we’re seeing is very dramatic,” said Andrew Fleming, remote sensing manager at the British Antarctic Survey. “It’s very worrying.”
Scientists believed the effects were linked to the “very strong warming” at the poles, he said. The Antarctic peninsula has warmed by more than 3ºC in the past 50 years. “That’s a staggering rate of warming, and it’s still going up,” said Mr Fleming.
Ice shelves take centuries to form, but when they start to break up it can be sudden. The bridge at the Wilkins ice shelf was a 40km strand of ice, at its narrowest point a few hundred metres wide, connecting the shelf to Charcot and Latady islands.
Last year, scientists from the BAS landed on it in an aircraft to examine the ice. They had known for some time it was under strain, but it remained intact until at the end of last week satellite images showed new cracks appearing.
The next day, the ice sheet had “exploded from the centre outwards”, said Mr Fleming, who was monitoring the break-up through satellite images from the European Space Agency.
“It was very fast, very dramatic,” he said. “It’s now completely shattered.”
The break-up of the ice bridge alarms scientists because it could accelerate the break-up of the rest of the Wilkins shelf. This was at least the 10th shelf to start disintegrating quickly in recent years, said Mr Fleming, and several more were in danger.
Rapid melting of polar sea ice is of particular concern for two reasons: disappearing ice leaves areas of open sea that are dark, and – unlike the reflective ice – absorb the sun’s heat, accelerating the warming process; the break-up of ice shelves exposes glaciers that then begin to move faster to the sea.
The Arctic and some of the Antarctic float on the sea. Ice takes up more space than water, and when this floating ice melts, it does not directly raise sea levels, in the same way that the melting of ice cubes in a full glass of water would not cause the glass to overflow.
However, the glaciers of the Antarctic peninsula are on land, so when they tumble into the sea, they contribute directly to rising sea levels. In the north, the Greenland ice sheet is also on land, and its glaciers are flowing faster to the sea.
If Greenland’s ice sheet melted, it would raise sea levels by seven metres, and if both the east and west Antarctic ice sheets went, the figure would be 10 times higher. That would take hundreds of years, according to the Intergovernmental Panel on Climate Change.
Long before the land ice disappeared, however, sea levels would rise significantly – a 1 per cent loss of the Antarctic land ice would probably raise levels by 65cm, estimates the Norwegian Polar Institute.
Two conferences this week were addressing the problems of the poles and climate change. At a joint meeting of the Antarctic Treaty and the Arctic Council in the US, Hillary Clinton, US secretary of state, said the news of the Wilkins ice shelf showed “global warming has already had enormous effects on our planet, and we have no time to lose in tackling this crisis”.
In Bonn, governments met for the first meeting to thrash out the details of a successor to the Kyoto protocol on climate change.
One factor that could help to slow the melting of the Arctic, but which has not yet received serious consideration internationally, would be to cut the amount of “black carbon” – soot – that we spew into the air. Black carbon darkens ice when it falls, causing it to absorb more heat, and may be responsible for half of the warming effect in the Arctic, according to research. Cutting soot would not only remove large amounts of air pollution, but, say some scientists, could be quicker and easier than cutting carbon dioxide emissions.
Copyright The Financial Times Limited 2009
By Fiona Harvey in Bonn
Published: April 10 2009 17:47 | Last updated: April 10 2009 22:59