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In hot water

In hot water DUNCAN WINGHAM is a worried man. Millions of people throughout the world living within one metre of the sea level - half a million in the Nile Delta itself - will lose their homes to the rising sea if his findings are correct. Global warming is causing a rise in the sea level at a pace faster than most scientists expected. And it is not the melting ice caps of Antarctica, which they have feared for a long time. It is something much simpler: sea level rises due to thermal expansion of warming waters, a result of global warming.

The researcher from University College, London, and his team carried out the first accurate measurement of the Antarctic ice cap using European remote sensing satellites. Their findings show that the ice sheet is scarcely shrinking as a result of global warming. But there is more than meets the eye: the findings confirm that the sea level is rising. It will rise by almost a metre over the next century.

The sea level is currently estimated to be rising by over 1.8 cm a decade. The percentage contribution of melting glaciers and ice caps to this rise remains a mystery. Researchers are also inconclusive about how much of this is due to the expansion of water as it warms.

Whatever affects the ice sheet in Antarctica is bound to have an impact on sea levels. As the ice sheet melts the largest store of freshwater on Earth will be released into the ocean. While the satellite survey implies that melting ice will play a minor role in raising the sea level, it also shows that the effect of thermal expansion is larger than expected.

While the prevailing conditions make it impossible to survey the ice cap, Wingharn and his colleagues used instruments aboard satellites to bounce radar and laser signals off the ice to compute its height. They concluded that on an average, the ice cap's height was changing by less than one cm per year. Only if the ice sheet shrinks by at least five cin per year will it raise the sea level significantly.

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