John Ezard
Climactic warming has destroyed part of the gigantic Larsen B ice shelf in Antarctica. Final disintegration and melting of the 19 500km2 shelf is now predicted within two years.
The crack-up, disclosed by a satellite photograph taken on March 23, confirmed and sharpened nearly a decade of anxiety about trends in a region which traps 90% of the world’s fresh water.
The worst scenario is that warming will spread south to the vastly bigger Ronne and Ross shelves, which are thought to pin back all the land ice of west Antarctica. The Ronne shelf – as big as Spain – begins only 640km south of Larsen B.
If these shelves broke away and the continental ice began to melt, global sea levels would rise by an estimated 5m to 6m. Low-lying areas, like Bangladesh, the Mississippi, Nile and Mekong deltas, the Netherlands, Lincolnshire and East Anglia, would become catastrophically flood-prone.
Matthew Spencer, climate campaigner for Greenpeace, said: “There is a risk that the continental ice shelves will be affected. The jury is still out on this.”
In the United States, Robert Bindshadler, chair of West Antarctic Ice Sheet Initiative, a scientific study group, has said recent rapid warming might create a “dynamic” chain reaction, with meltdowns spreading south.
But most scientists say this would only happen in 200 to 500 years – if at all. “We don’t expect climatic change to swarm across the world in quite that way,” said David Vaughan, glaciologist for the British Antarctic survey. “Nobody is saying at the moment that we are going to lose the west Antarctic land ice.”
From computer and climate models, Bill Budd, professor of meteorology at Australia’s Antarctic Co- operative Research Centre, predicted “significant degradation” beginning in the next century and near-total loss of the ice shelves within 500 years.
He said the ongoing ice shelf collapse was consistent with “what we see from the effects of increased greenhouse gases, which cause warming”.
The collapse of 195km2 of Larsen B was spotted by a US oceanic and atmospheric satellite.
Ted Scambos, of the National Snow and Ice Data Center, Boulder, Colorado, who has analysed the satellite images, said: “The question now is what is causing the reduction in sea ice. At this point, we do not have enough evidence to find a smoking gun.”
The shelf is the fourth known to have broken up in a decade during which worried observers have seen melting icebergs drift far north of the Falkland Islands.
Its expected disappearance will be Antarctica’s biggest ice loss in 20 years. Two years ago, the smaller Larsen A shelf broke up unprecedently during a single storm, after years of shrinkage.
Both shelves formed up to 10 000 years ago next to Grahamland on the Antarctic Peninsula, the region’s warmest, most northerly tip. Since the 1940s, temperatures on the peninsula have risen by 2,5 C (4,5 F), a rate several times the world average.
So far no comparable temperature rise has been measured in the rest of Antarctica. Vaughan believes the widespread upward trend in the peninsula “is almost certainly a result of local conditions there. We suspect an instability in the local climate.
“This could be linked to ocean circulation, the amounts of sea ice forming, routes of depressions, and other factors that may have nothing to do with Antarctica.”
Glaciologists cannot agree on whether ice shelves do act as bastions holding in land ice. “It is the biggest controversy in our field at present,” Dr Vaughan said.
Scambos said: “Ice shelves appear to be good bellwethers for climate change. They respond to change within decades, rather than the years or centuries of other climate systems.”
Last year the Greenpeace vessel Arctic Sunrise found lagoons, rivers and 500m-long rifts on Larsen B. The pressure group said: “It has taken centuries to millennia for these vast bastions to form. Now, under the pressures of human activities, they are crumbling to nothing.”
ENDS