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Ice caps melting faster than forecast

Ice caps melting faster than forecast
`It's not a gradual change. It's like flipping a switch,' researcher says
New reports warn of sea levels rising up to 5 metres, extensive flooding
Mar. 24, 2006. 10:17 AM
PETER CALAMAI
SCIENCE REPORTER

Global warming of only a couple of degrees Celsius projected by the end of this century is enough to trigger widespread melting of the massive Greenland ice cap and the partial collapse of Antarctica's ice sheets, prominent climate researchers warn in two studies published yesterday.

The findings are a stunning about-face from previous expert forecasts that such massive melting would take millennia to kick in, even with rising global atmospheric levels of carbon dioxide and other greenhouse gases.

This new research, based on a comprehensive look at global warming in the distant past, says melting the two icy domains could eventually raise sea level worldwide by as much as five metres, enough to flood low-lying regions like the Netherlands and most Pacific atolls, as well push half a billion people inland.

The full five-metre rise could take several centuries but the world's oceans could easily be a metre higher by 2100, the researchers said.

"The melting is going to happen faster than we thought. It's already begun to happen," said University of Calgary ice researcher Shawn Marshall, the sole Canadian among the authors of the two studies published by the journal Science.

"We could be past the point of no return for Greenland this century," he said in an interview.

A 1998 federal government report rated most of P.E.I., the eastern coast of Nova Scotia and the Beaufort Sea shore in the Western Arctic as "highly sensitive" to a global sea level rise of under seven-tenths of a metre.

Marshall and the other researchers acknowledged they were taken by surprise by the breakneck escalation in the melting of glaciers and ice sheets in recent years. Since 1980 the portion of the Greenland ice cap experiencing annual melting has increased by 40 per cent.

"It's not a gradual change. It's like flipping a switch. Areas that haven't experienced melt in centuries suddenly do," said Marshall.

A widely quoted report in 2001 from the Intergovernmental Panel on Climate Change concluded that major melting was no threat in Greenland and Antarctica in this century.

But Jonathan Overpeck, a climate scientist at the University of Arizona, said the new research shows these massive ice sheets are much more sensitive to global warming than originally suspected.

"Once we're above two times the pre-industrial levels of carbon dioxide we're in the danger zone," said Overpeck, who is lead author on one of the studies.

`The melting is going to happen faster than we thought. It's already

begun to happen.

We could be past the

point of no return for

Greenland this century.'

Shawn Marshall, University of Calgary

"Somewhere after that we'll pass a threshold where melting of the ice sheets and sea level rise is irreversible," he said.

Most experts agree that carbon dioxide concentrations double the pre-industrial level will be reached sometime after 2050 unless global emissions are at least cut in half. The current atmospheric concentration of carbon dioxide is about 380 parts per million compared to 280 parts per million before widespread burning of fossil fuels began around 1870.

Under the Kyoto Protocol, industrialized countries have pledged to reduce their overall emissions of greenhouse gases to 5 per cent below 1990 levels starting in 2008.

But soaring emissions from China and other developing countries — and the Kyoto boycott by Australia and the United States — mean that global carbon dioxide levels are expected to continue rising steadily.

The new warning is based on using climate extremes from the last major global warming to check the reliability of future climate conditions projected by complex computer models.

A prolonged hot spell began 129,000 years ago because natural orbital variations caused the Earth's northern axis to tilt more toward the sun producing much higher temperatures in the northern hemisphere, especially the Arctic.

A decade-long international research project gathered an evidence of climate change from that period, including the disappearance of glaciers in Canada's Arctic archipelago, halving of Arctic sea ice coverage, major shrinking of the Greenland ice cap and a northward march of the boreal forest.

Examination of Australia's Great Barrier Reef also indicated that sea levels were four to six metres higher than today.

A group of U.S. researchers then produced many of the same results by simulating increased sun on the northern hemisphere in an advanced climate model which Calgary's Marshall beefed up to handle glacier movements and ice melting.

"The model got it about right for the past which gives us more confidence in its forecasts," said Marshall.

A second research team, led by Overpeck, then used the souped-up model to project what would happen to the Earth's ice cover if global temperatures were raised by higher levels of carbon dioxide rather than a shift in the planet's tilt.

They found that tripling pre-industrial carbon dioxide levels by 2100 caused widespread melting in Greenland and the Arctic but didn't raise sea levels the five metres recorded in the Australia reefs. The Western Antarctic Ice Sheet must also melt, the scientists concluded.

Even a two degree Celsius rise in global average temperature would cause thermometers to soar as much as eight or 10 degrees in the Arctic and Antarctic, a feedback process known as polar amplification.

"All the things we were worrying about happening did happen and it didn't take that much warming," said Overpeck.

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