The frozen “cryosphere” of the Earth, from the Arctic sea in the north to the massive ice shelves of Antarctica in the south, is showing the unequivocal signs of climate change as global warming accelerates the melting of the coldest regions of the planet, leading polar scientists warned yesterday.
A rapid loss of ice is clear from the records kept by military submarines, from land measurements taken over many decades and from satellite observations from space. It can be seen on the ice sheets of Greenland, the glaciers of mountain ranges from the Andes to the Himalayas, and the vast ice shelves that stretch out into the sea from the Antarctic continent, the experts said.
The effect of the melting cryosphere will be felt by rapidly rising sea levels that threaten to flood coastal cities and low-lying nations, changes to the circulation of ocean currents such as the Gulf Stream, and possible alterations to the weather patterns that influence more southerly regions of the northern hemisphere, they said.
One of the greatest threats is the melting of the permafrost regions of the northern hemisphere which could release vast quantities of methane gas from frozen deposits stored underground for many thousands of years. Scientists are already seeing an increase in methane concentrations in the atmosphere that could be the result of melting permafrost, they said.
“The melting of the cryosphere is such a clear, visibly graphic signal of climate change. Almost every aspect is changing and, if you take the global average, it is all in one direction,” said Professor David Vaughan, a geologist at the British Antarctic Survey in Cambridge.
One of the clearest signals of climate change is the rapid loss of floating sea ice in the Arctic, which has been monitored by satellites since the late 1970s and by nuclear submarines since the beginning of the cold war, said Professor Peter Wadhams of Cambridge University, one of the first civilians to travel under the Arctic sea ice on a nuclear submarine.
The sea ice is retreating faster and further than at any time on record and this year it probably reached an all-time record minimum in terms of volume and a close second in terms of surface area. On current projections, if the current rate of loss continues, there could be virtually no September sea ice as early as 2015, Professor Wadhams said at a briefing held at the Science Media Centre in London.
“The changes are more drastic that we thought. The effect is more dramatic than if you just look at the surface area of the ocean covered by sea ice. Submarine records show a big area north of Greenland is reduced in sea ice thickness,” Professor Wadhams said.
The loss of sea ice and the warming of the Arctic region is having an impact on the permafrost regions of the north, both on land and in the shallow sea above the continental shelf of northern Russia, he said. Scientists have documented vast methane releases both on land and above the sea.
“Methane is 23 times more potent as a greenhouse gas than carbon dioxide. We can expect the possibility of a methane boost to global warming. We have to warn about the loss of sea ice, and the retreat is accelerating,” Professor Wadhams said.
One of the greatest threats in the coming century will be the possible rapid rise in sea levels as a result of melting mountain glaciers and polar ice sheets. Scientists believe that about two thirds of the current rate of average sea level rise, about 3 millimetres a year, is the result of melting ice, both from mountain glaciers and polar ice sheets.
“In a warmer world, one thing you can guarantee is that ice will melt. Sea levels are now rising at a third of the rate they were when we had truly massive ice sheets at the end of the last ice age,” said Chris Rapley, professor of climate science at University College London, and a former head of the British Antarctic Survey.
Some parts of the Antarctic, such as the Pine Island Glacier, are melting faster than at any time on record and the melting is outstripping the growth of glaciers in other regions of the Antarctic continent that are higher, colder and with more snowfall, said Professor Rapley said.
Greenland is also seeing an unprecedented melting of its glaciers. Since the 1990s, the Greenland ice sheet has lost mass at an ever-accelerating rate, a loss that could be responsible for about 30 per cent of the sea-level rise by the year 2100, said Professor Jonathan Bamber of Bristol University. At the same time, average temperatures around Greenland are forecast to rise by between 6C and 7C, which is about two or three times the global average, he said.
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