LONDON - Thousands of scientists from across the world join forces this week to investigate the effects of global warming on the Arctic and Antarctic ice sheets.

The ice in both polar regions is melting more rapidly than anywhere else, leading to rises in sea levels and possibly to dramatic changes in ocean currents and food chains.

International Polar Year, which will run to 2009, will involve 50,000 people from 63 nations in 228 projects looking at and under the ice, in the sea and in the atmosphere in the biggest coordinated polar study for half a century.

"The reality is we know so little. The difference is that we know how important it is," Martin Siegert of Edinburgh University said at the London launch, one of several around the world before the main event in Paris on Thursday.

One estimate suggests that if the vast Greenland ice sheet disappears, sea levels around the world will rise by seven meters, drowning huge areas of the planet.

That fades into insignificance against the 200-meter sea level rise expected if all the Antarctic ice melts.

"Global warming is the most challenging problem our society has ever had to face up to," said Britain's chief scientist David King.

"Ice is the canary in the coalmine of global warming."


World scientists predicted this month that average world temperatures will rise by between 1.8 and 4.0 degrees Celsius this century due mainly to carbon gases from burning fossil fuels for power and transport.

This is a global average, however, and the temperature rises at the poles are expected to exceed that by a large margin.

Scientist Corinne Le Quere of the British Antarctic Survey said atmospheric concentrations of the main greenhouse gas carbon dioxide had fluctuated between 180 and 280 parts per million (ppm) for 650,000 years.

Since 1850 they had shot up to over 380 ppm. "We are on an unsustainable path," she said.

The Antarctic ice sheet is up to 4.8 kilometres (3 miles) thick in places and it holds 90 percent of the world's fresh water. It is also crucial to the circulation of the world's ocean currents and therefore to planetary air circulation.

In the Arctic, critical to the North Atlantic thermohaline circulation -- also known as the Gulf Stream -- the problems also involve the four million people who live in the region.

Already global warming is reducing the area of ocean ice by three percent every decade.

Adding to the pressure, geologists calculate the Arctic may contain up to 25 percent of the world's untapped oil reserves.