Magazine article Geographical

Shock and Thaw: The Arctic and Antarctic Are the World's Freezers, Together Storing More Than 90 per Cent of the World's Fresh Water as Ice. but Global Climate Change Has Wedged Open the Freezer Door, Defrosting the Colossal Polar Ice Masses at an Alarming Rate. the Warnings from Scientists Are Loud and Stark-But Just What Is the Current State of the Poles, and How Much Worse Is It Going to Get?

Magazine article Geographical

Shock and Thaw: The Arctic and Antarctic Are the World's Freezers, Together Storing More Than 90 per Cent of the World's Fresh Water as Ice. but Global Climate Change Has Wedged Open the Freezer Door, Defrosting the Colossal Polar Ice Masses at an Alarming Rate. the Warnings from Scientists Are Loud and Stark-But Just What Is the Current State of the Poles, and How Much Worse Is It Going to Get?

Article excerpt

Classified satellite photographs usually involve missile sites or nuclear power installations. But last summer, images of melting ice caps emerged as another category deemed worthy of being kept under lock and key. The pictures, kept from public eyes during George W Bush's presidency, were among 1,000 images showing the impact of global warming that were declassified by the Obama administration.

Among the most striking was one of solid sea ice around the Alaskan port of Barrow in July 2006, and another, taken a year later in the same area, depicting ice-free waters.

The detailed one-metre-resolution images were unambiguous evidence of the nature of the evaporating ice sheets. They were reinforced by a study of satellite measurements involving NASA's Goddard Space Flight Center that found that Arctic ice, typically up to about three metres thick, had thinned by 67 centimetres over the past four winters.

'The trend is very clear and simply astonishing,' says Dr Ron Kwok, senior researcher for NASA's Jet Propulsion Laboratory. 'This is a very clear signal of global warming. We're seeing a lot more seasonal thin ice rather than perennial ice.' Between 2005 and 2008, according to NASA, there was a 42 per cent drop in the amount of thick ice. Last year, multi-year ice, which is generally more than 2.5 metres thick, covered about one third of the Arctic Ocean--before 2005, the area covered was more than half the total.

Arctic ice--which, according to the British Antarctic Survey (BAS), has been a permanent feature for at least 100,000 years--is disappearing before our eyes. The total absence of summer ice is, by almost all accounts, now a foregone conclusion in a matter of years.

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'Multi-year ice is now confined to quite a small area near Greenland and Ellesmere Island--perhaps two million square kilometres,' says Professor Peter Wadhams of the Polar Oceans Physics Group at the University of Cambridge. 'In 2007, the absolute minimum area of ice in the Arctic was 4.2 million square kilometres. Half of the ice that remains is first-year ice [less than two metres thick and which retreats, thins and melts in summer].'

GRIM UP NORTH

But it isn't only the state of ice over the Arctic waters that is causing disquiet. The Greenland ice sheet, which covers the bulk of the world's largest non-continental island, is also under intense scrutiny. The ice sheet, the WWF points out, holds enough water to raise global sea levels by seven metres if it were to melt. Observations of the ice sheet from the ground, airborne platforms and satellites show that more ice is being lost to the ocean than is being formed to maintain it. Last year, this mass loss was about 280 gigatonnes per year, and has increased by 20 gigatonnes every year since the 1980s. For comparison, a large city such as Los Angeles uses about one gigatonne of water a year. The WWF calculates that if the ice sheet continues to lose mass at this rate, sea levels will rise worldwide by 31 centimetres from Greenland water sources alone by 2100.

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According to the WWF's Arctic Climate Feedbacks: Global Implications report, published this autumn, the melting on the surface of the Greenland ice sheet in 2007 was by far the most extensive since records began. The area experiencing surface melt was 60 per cent larger than in 1998, when the second-highest level of melting was recorded. In 2007, some areas of the Arctic that were free of surface-water ice were as much as 5[degrees]C higher than the long-term average, according to the report.

'Arctic Ocean waters have been warming in recent years, because declining sea-ice cover allows the water to absorb more heat from the sun,' notes the report. 'The Arctic Ocean has also warmed as a result of the influx of warmer water from the Pacific and Atlantic oceans.' In addition, the World Meteorological Organization (WMO) reports that studies conducted during the winter of 2007-08 showed that the North Pole region was covered only in relatively thin first-year ice in midwinter for the first time in observational history. …

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