Abrupt climatic shifts could overtake US sooner than later

December 20th, 2008 - 1:30 pm ICT by IANS  

Washington, Dec 20 (IANS) Abrupt climatic shifts could overtake the US if melting polar ice continues to outrun recent projections, according to a government report. Many scientists also apprehend the possibility that abrupt, catastrophic switches in natural systems is likely to punctuate the steady rise in global temperatures now underway.

The report commissioned by the US Climate Change Science Program, was authored by experts from Geological Survey, Columbia University’s Lamont-Doherty Earth Observatory and other leading institutions.

However, the likelihood and timing of such “tipping points,” where large systems move into radically new states, has been controversial. The new report synthesises the latest published evidence on four specific threats for the 21st century.

It uses studies not available to the Intergovernmental Panel on Climate Change (IPCC), whose widely cited 2007 report explored similar questions.

“This is the most up to date, as it includes research that came out after IPCC assembled its data,” said Edward Cook, a climatologist at Lamont-Doherty and co-author of the new study.

The researchers said the IPCC’s maximum estimate of two feet of sea level rise by 2100 may be exceeded, because new data shows that melting of polar ice sheets is accelerating.

Among other things, there is now good evidence that the Antarctic ice cap is losing overall mass. Seaward flow of ice from Greenland is also accelerating.

However, projections of how far sea levels might rise are “highly uncertain,” says the report, as researchers cannot say whether such losses will continue at the same rates.

In the interior US, a widespread drought that began in the Southwest about six years ago could be the leading edge of a new climate regime for a wider region, said a Columbia University release.

Cook, who heads Lamont’s Tree Ring Lab, says that periodic droughts over the past 1,000 years have been driven by natural cycles in air circulation, and that these cycles appear to be made more intense and persistent by warming.

Among the new research cited is a 2007 Science paper by Lamont climate modeller Richard Seager, showing how changes in temperature over the Pacific have driven large-scale droughts across western North America.

“We have no smoking gun saying that humans are causing the current changes. But the past is a cautionary tale,” Cook told the press conference.

“What this tells us is that the system has the ability to lock into periods of profound, long-lasting aridity. And there is the suggestion that these changes are related to warmer climate.”

Cook added: “If the system tips over, that would have catastrophic effects no human activities and populations over wide areas.”

The panel said two other systemic changes seem less imminent, but are still of concern. Vast quantities of methane, a potent greenhouse gas, have long been locked up in ocean sediments, wetlands and permafrost.

These could be destabilised by climate change, leading to blowouts of gas, and thus even more abrupt temperature shifts.

It was released at this week’s meeting of the American Geophysical Union.

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