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Drinking rainwater from banana leaf, Nigeria. (c) I. Uwanaka/UNEP
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climate change > factfile > ice melt and sea level

Ice melt and sea level

Posted: 01 Apr 2006

The Intergovernental Panel on Climate Change believe that if current trends continue sea levels will rise by 9 and 88 centimetres within 80 years. This broad range is indicative of the uncertainties involved in climate science and all predictions about future sea level rises, and their consequences, are necessarily tentative. A sea level rise of 50 cm would represent an increase of 1.5 to 3.5 times on the historic rate of sea level rise occurring without man's interference.

See charts on sea rise in relation to global warming

  • Arctic sea-ice draft (the thickness of the part of the ice that is submerged under the sea) in the 1990s was over a metre thinner than two to four decades earlier. The main draft has decreased from over 3 metres to under 2 metres, and the volume is down by some 40 per cent. NASA satellite imagery suggests that Arctic sea ice is shrinking at the edges by 2.9 per cent a decade.

Scientists believe the thinning of the Arctic sea ice is a result of two causes. Rising air temperatures, possibly the consequence of global warming, are melting the ice from above. And warmer water is also rising from the depths to attack the ice from below.

  • Research by the National Oceanic Atmospheric Administration in the United States suggests that much of the heat of global warming may presently be stored in the oceans, thus reducing atmospheric rises, but threatening huge climatic changes in the future. Most of the data was gathered by research ships, naval ships, merchant ships and buoys. However, recent research by an international team of scientists has found serious discrepancies in the sea temperature measurements, and suggest that the rate of global warming may consequently have been exaggerated by as much as 40 per cent.

  • The overall annual loss of Greenland's ice sheet mass has more than doubled from 90 cubic kilometres a year in 1996 to 224 cubic kilometres per year in 2005, according to a report published in Science. Air temperatures over Greenland have risen by 3� C over the past 20 years. And as the water has melted it has lubricated the interface between glaciers and the rocks below, speeding the glaciers' march into the ocean, the authors say. They calculate that Greenland contributes 0.5 mm per year to global sea level rise - out of an estimated total of 3mm.

  • Global warming could lead to more damaging storm surges. Model-based studies suggest that the number of people flooded each year by "super storm surges" could increase five-fold by 2080.

  • Rising sea levels increase the risk of coastal flooding, and may necessitate population displacement. More than half of the world's population now lives within 60km of the sea. Some of the most vulnerable regions are the Nile delta in Egypt, the Ganges-Brahmaputra delta in Bangladesh, and many small islands, such as the Maldives, the Marshall Islands and Tuvalu.

  • The 22 countries and territories in the Pacific Ocean have contributed under 0.06 per cent to global greenhouse gas emissions. Two small islets have already disappeared in Kiribati and many low lying islands are experiencing accelerated coastal erosion.

  • According to Third World Network, data provided by the Australian National Tidal Centre (NTC) "show a sea-level rise of up to one inch each year, well above the global estimate for a tenth-of-an-inch annual rise made by the Intergovernmental Panel on Climate Change." Yet according to a recent NTC study, sea levels have risen by an average of only 0.8mm per year at its Pacific recording stations where hourly data stretching back more than 25 years has been kept. "There is no acceleration in sea level rise - none that we can discern at all," Dr Wolfgang Scherer, NTC's Director, told the BBC. If nothing else, this highlights the need to assess all climate change information with great caution.

  • The melting of the Arctic ice will not cause flooding directly. But the melting of ice hastens the process of global warming. White ice reflects heat; dark water absorbs it.

Related links:

Scott Polar Research Institute

NOAA's Arctic page

Norwegian Polar Institute

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