http://www.timesonline.co.uk/article/0,,8122-1067480,00.html
GREENLAND?s ice sheet is almost certain to melt away, raising sea levels by seven metres, unless more ambitious targets are set for reducing global warming.
A new analysis shows that within half a century, carbon dioxide levels in the atmosphere will be high enough to start the huge ice sheet melting.
The melting would take a long time, as much as 1,000 years, but the effects on sea level would be catastrophic. A rise of 7m (23ft) would be enough to inundate huge areas of land, with entire countries, such as the Maldives, disappearing.
Large areas of Britain would disappear under the waves if sea levels rose by 7m. Sea defences around East Anglia and the Somerset Levels would be washed away and the estuaries of major rivers would also face inundation from floods of water. The Thames Barrier could not cope with anything like an increase in sea level and large parts of Central London, including many prime sites, would be at risk.
?Unless much more substantial emission reductions are made than those envisaged by the Intergovernmental Panel on Climate Change (IPCC), the Greenland ice sheet is likely to be eliminated,? a team of climatologists led by Jonathan Gregory, of the Centre for Global Atmospheric Monitoring at the University of Reading, concluded. Scientists have previously calculated that if Greenland?s annual temperature increased by more than about 3C its ice sheet could eventually disappear. There is a ?threshold? temperature rise of 2.7C, above which the melting of the ice sheet exceeds the snowfall and it begins to shrink.
The new research shows that this threat is far more real than most people had thought. It suggests that greenhouse gas levels will probably reach this threshold well before the end of the century.
At present, about half the snow falling on Greenland melts and runs off as water. The remainder is discharged in the form of icebergs.
Climate change caused by greenhouse gases such as carbon dioxide is expected to produce both warmer temperatures and greater precipitation.
But most studies predict that the higher rates of melting will outweigh increases in snowfall in Greenland.
The team, writing in Nature, used computer models of the climate to work out Green-land?s future temperature, using a range of scenarios in which carbon dioxide levels in the atmosphere stabilise at different levels. The prediction varies with the model, and with the different stabilisation levels of carbon dioxide, so the team ran a range of different models, with different levels. In 34 out of 35 runs, the temperature increases exceeded the 2.7C threshold.
?Warming exceeds 8C in many cases and continues to rise after 2350 for the higher concentrations,? the team says in the magazine.
The lowest carbon dioxide level considered was 450 parts per million ? a level due to be exceeded by 2050, according to the best estimates of the IPCC. Given this and the fact that carbon dioxide is not the only global warming gas, the team concludes that the ice sheet is in all probability doomed.
Even if the composition of the atmosphere and the global climate were to return to pre-industrial levels, the ice sheet might never return, the climatologists say. The reason is that without the ice, the land would reflect less sunlight and be much warmer.
In addition, the land surface would be at a lower altitude, and therefore warmer for that reason as well. ?We conclude that the Greenland ice sheet is likely to be eliminated by anthropogenic climate change unless much more substantial emission reductions are made than those envisaged by the IPCC. This would mean a global average sea-level rise of 7m during the next 1,000 years or more.?
The only international agreement on cutting greenhouse gases is the UN?s Kyoto protocol, which requires industrial countries to make a small cut in globalemissions by 2008-12. But the pact is in limbo. It still needs ratification by Russia to take effect and in any case has been abandoned by the United States, the world?s biggest polluter.
DEEP FREEZE
The Greenland ice sheet covers more than 700,000 square miles, 85 per cent of Greenland?s total area
At the centre, the ice is anything up to two miles thick and represents 10 per cent of the world?s total fresh-water reserves
Unlike Arctic ice, the Greenland and Antarctic ice sheets lie on rock rather than floating. That means if they melt they will raise the level of the oceans
Previous studies have shown that the Greenland ice sheet is already thinning, in some places by as much as 3ft a year. This could account for about 7 per cent of the observed rise in sea levels that has occurred in recent years
Greenland was so-called because when settled by the Norwegian Eric the Red in the 10th century, it was green. The Norse settlers were eventually forced out as the climate worsened
GREENLAND?s ice sheet is almost certain to melt away, raising sea levels by seven metres, unless more ambitious targets are set for reducing global warming.
A new analysis shows that within half a century, carbon dioxide levels in the atmosphere will be high enough to start the huge ice sheet melting.
The melting would take a long time, as much as 1,000 years, but the effects on sea level would be catastrophic. A rise of 7m (23ft) would be enough to inundate huge areas of land, with entire countries, such as the Maldives, disappearing.
Large areas of Britain would disappear under the waves if sea levels rose by 7m. Sea defences around East Anglia and the Somerset Levels would be washed away and the estuaries of major rivers would also face inundation from floods of water. The Thames Barrier could not cope with anything like an increase in sea level and large parts of Central London, including many prime sites, would be at risk.
?Unless much more substantial emission reductions are made than those envisaged by the Intergovernmental Panel on Climate Change (IPCC), the Greenland ice sheet is likely to be eliminated,? a team of climatologists led by Jonathan Gregory, of the Centre for Global Atmospheric Monitoring at the University of Reading, concluded. Scientists have previously calculated that if Greenland?s annual temperature increased by more than about 3C its ice sheet could eventually disappear. There is a ?threshold? temperature rise of 2.7C, above which the melting of the ice sheet exceeds the snowfall and it begins to shrink.
The new research shows that this threat is far more real than most people had thought. It suggests that greenhouse gas levels will probably reach this threshold well before the end of the century.
At present, about half the snow falling on Greenland melts and runs off as water. The remainder is discharged in the form of icebergs.
Climate change caused by greenhouse gases such as carbon dioxide is expected to produce both warmer temperatures and greater precipitation.
But most studies predict that the higher rates of melting will outweigh increases in snowfall in Greenland.
The team, writing in Nature, used computer models of the climate to work out Green-land?s future temperature, using a range of scenarios in which carbon dioxide levels in the atmosphere stabilise at different levels. The prediction varies with the model, and with the different stabilisation levels of carbon dioxide, so the team ran a range of different models, with different levels. In 34 out of 35 runs, the temperature increases exceeded the 2.7C threshold.
?Warming exceeds 8C in many cases and continues to rise after 2350 for the higher concentrations,? the team says in the magazine.
The lowest carbon dioxide level considered was 450 parts per million ? a level due to be exceeded by 2050, according to the best estimates of the IPCC. Given this and the fact that carbon dioxide is not the only global warming gas, the team concludes that the ice sheet is in all probability doomed.
Even if the composition of the atmosphere and the global climate were to return to pre-industrial levels, the ice sheet might never return, the climatologists say. The reason is that without the ice, the land would reflect less sunlight and be much warmer.
In addition, the land surface would be at a lower altitude, and therefore warmer for that reason as well. ?We conclude that the Greenland ice sheet is likely to be eliminated by anthropogenic climate change unless much more substantial emission reductions are made than those envisaged by the IPCC. This would mean a global average sea-level rise of 7m during the next 1,000 years or more.?
The only international agreement on cutting greenhouse gases is the UN?s Kyoto protocol, which requires industrial countries to make a small cut in globalemissions by 2008-12. But the pact is in limbo. It still needs ratification by Russia to take effect and in any case has been abandoned by the United States, the world?s biggest polluter.
DEEP FREEZE
The Greenland ice sheet covers more than 700,000 square miles, 85 per cent of Greenland?s total area
At the centre, the ice is anything up to two miles thick and represents 10 per cent of the world?s total fresh-water reserves
Unlike Arctic ice, the Greenland and Antarctic ice sheets lie on rock rather than floating. That means if they melt they will raise the level of the oceans
Previous studies have shown that the Greenland ice sheet is already thinning, in some places by as much as 3ft a year. This could account for about 7 per cent of the observed rise in sea levels that has occurred in recent years
Greenland was so-called because when settled by the Norwegian Eric the Red in the 10th century, it was green. The Norse settlers were eventually forced out as the climate worsened
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