THE ancient frozen dome cloaking Greenland is so vast that pilots have crashed into what they thought was a cloud bank spanning the horizon. Flying over it, you can scarcely imagine that this ice could erode fast enough to raise sea levels to dangerous levels any time soon. It is too vast, and seemingly too solid.
Yet along the flanks of the glacier in spring and summer, the picture is very different. For a lengthening string of warm years, a lacework of blue lakes and rivulets of meltwater have been spreading over the ice cap. The melting surface darkens, abs
orbing up to four times as much energy from the sun as unmelted snow, which reflects sunlight.
Glaciologists have now discovered that natural drainpipes called moulins are carrying water from the surface into the depths, in some places reaching bedrock. The process slightly, but measurably, lubricates and accelerates the grinding passage of ice as it slips towards the sea.
Where large Greenland glaciers squeeze through fjords and break up as they meet the warming ocean, this phenomenon has sharply accelerated the flow of many of these creeping, corrugated, frozen rivers.
This recently spotted phenomenon has left many glaciologists with a feeling of dread. Ted Scambos, the lead scientist at the National Snow and Ice Data Centre in Boulder, Colorado, and a veteran of both Greenland and Antarctic studies, said he was "shellshocked" by the unexpected speed at which these mountains of ice were now melting.
The fear now is that the rise in sea levels in a warming world could be much greater than the estimate of about two feet this century made by the Intergovernmental Panel on Climate Change (IPCC) last year. By contrast, seas rose less than a foot in the 20th century.
The melting of the Greenland ice cap thousands of miles away may seem a remote threat to the communities living around the coast of Scotland. But there is a growing scientific consensus that it represents a serious global threat to all countries in the northern hemisphere.
So if the estimates prove correct, do we need to rethink our assumptions about global warming? Should there be a fresh urgency in the moves towards new international agreements on carbon emissions? And how much of Scotland is likely to disappear under water if we fail to act?
Earlier this year, alarming new simulations of the threat posed were produced by Johnathan Overpeck, a member of the IPCC panel and professor of geosciences at Arizona University. Although the panel forecast average rises of two feet, regional variations suggested sea level rises of up to three feet around the British coastline.
The implication of this would be severe. The Edinburgh coastline could retreat a mile inland, swamping northern areas of the city along the Firth of Forth. Half of Alloa would end up under water and Fife coastal towns such as Methil and Buckhaven could be submerged.
Further north, the area along the Tay estuary west of Dundee would be flooded, as would parts of Cromarty and the Black Isle. John O' Groats would be on a new island formed as the sea rushed through low-lying land to the south to connect the Pentland Firth and the North Sea through a new channel.
On the west coast, western sections of Dumbarton along the Clyde would be under water and the southern parts of the Rhinns of Galloway would become an island. Much of Iona would disappear, as would large parts of Coll, Tiree and Lismore. Lewis would split into four islands and North and South Uist into two each.
The Scottish Environment Protection Agency, which oversees flood prevention, estimates around 18,000 coastal properties are at risk from rising sea levels.
Overpeck says the threat must now be scrutinised in a whole new light. "Our maps underline the urgency of the whole issue and how we have to address global warming now. A metre rise is the maximum we can expect for this century but the risk is that through our actions we essentially commit to melting the larger ice sheets, which could cause an even greater rise in sea levels."
The scientific scramble is now underway to clarify what is going on, much of it using satellite technology.
The Arctic Council, representing countries with Arctic territory, has commissioned a report on Greenland's environmental trends, to be completed before the 2009 climate treaty talks in Copenhagen, at which the world's nations have pledged to settle on a long-term plan for limiting human-caused global warming.
The Copenhagen process will replace the Kyoto Agreement, under which many of the world's leading nations – the US being a notable absentee – pledged to work towards reducing damaging emissions of the greenhouse gases, such as carbon dioxide, behind global warming.
In Bali last month, political leaders meeting for the UN's Climate Change Summit reached a deal which launches formal negotiations with a 2009 end date. Under pressure to conform, the US delegation agreed to join the talks to put on track a future treaty that would cut developed countries' emissions to 25-to-40% below 1990 levels by 2020.
The environmental movement said that while the deal lacked substance at this stage, US involvement, albeit belated, was welcome.
Aubrey Manning, the emeritus professor of natural history at Edinburgh University, says the residents of most countries are still "in denial" about the effects global warming and rising sea levels could have on them.
"In the western world we have comfortable lifestyles and we can't believe that our toys will be taken away from us in this way," said Manning, who, next month in Edinburgh, will give this year's prestigious Hawthornden Lecture on the threats facing the planet. "But I think that with the recent experiences of severe flooding and more frequent violent storms we have begun to realise the effects are all too real. Governments are taking action but we all have to play our part in reducing carbon emissions if we want real change."
While politicians argue about the path ahead and the public seeks clear guidance on how to react, the scientists are still trying to work out how quickly the melting ice sheets could threaten global lifestyles.
Last August, Konrad Steffen, an experienced University of Colorado glaciologist,
dropped a camera 330ft down a water-filled moulin to explore whether the glacier's plumbing system can be mapped.
Research on alpine glaciers shows that as more water flows through such apertures, ice can shift more quickly. One hope is that eventually large sewer-like conduits will form, limiting the lubrication effect.
Alberto Behar, a Nasa engineer who designed the camera, said some unconventional methods were being considered to chart the flow of such water. "We had ideas to send rubber ducks down and see if they pop out in the ocean," he said. "They'd have a little note saying, 'Please call this number if you find me.'"
It is possible that the changes seen in Greenland may turn out to be self-limiting in the short run. Surging glaciers can flatten out and slow, for instance. But worryingly, the opposite could be true in that the changes may be a sign that the island's ice – holding about the same volume of water as the Gulf of Mexico – is poised for a rapid discharge.
Scientists are divided on that question, and on whether there is a short-term risk from a portion of West Antarctica's ice sheet a quarter of a million square miles in area that is showing signs of instability. While a few experts speak of a rise in sea levels of yards, not feet, those holding a more conservative view of Greenland's near-term fate include Richard Alley of Pennsylvania State University, who noted that ice cores and tests of organic material from beneath the ice suggested the main mass of the Greenland ice sheet endured thousands of years of warming in the past without vanishing.
"It's basically a big lump of ice sitting on this bedrock," Dr Alley said in describing Greenland's behaviour in warm conditions. "What it tries to do is snow more in the middle and melt more on the edges. If it pulls its edges back, then there's less area to melt, and that helps it survive. That's why you can have a stable ice sheet in a warmer climate."
But there is no longer any significant debate on the long-term picture. Should greenhouse gas emissions follow anything close to a "business as usual" rise, the resulting warming and ice loss at both ends of the earth would cause coasts to retreat for centuries. The IPCC panel was grimly confident about that long view.
The prospect of having no "normal" coastline for the foreseeable future has many scientists deeply concerned.
"What is at stake is the stability we have always taken for granted, both for coasts and climate itself," said Jason E Box, an associate professor of geography at Ohio State University.
Eric Rignot, a long-time student of ice sheets at both poles for Nasa's Jet Propulsion Laboratory, said he hoped the public and policymakers did not interpret uncertainty in the 21st-century forecast as reason for complacency on the need to limit risks by cutting emissions.
He has said unabated warming could result in three feet of global sea rise just from water flowing off Greenland, three feet from Antarctica and 18 inches as the remaining alpine glaciers shrivel away.
"It is too early to reassure that all will stabilise, and similarly there is no way to predict a catastrophic collapse. But things are definitely far more serious than anyone would have thought five years ago."
The full article contains 1614 words and appears in Scotland On Sunday newspaper.
