Another International Polar Year (IPY) is set for launch on Thursday but the big difference is that in 2007, the entrenched dread of the planet's two extremes has been replaced by deepening concern for them.

Today, the North and South Poles' image of hostility has been replaced by one of benevolence.

The Arctic and Antarctic are now seen as unique stores of wildlife and precious reservoirs of cold imperilled by global warming and their fate is inextricably bound with ours.

"IPY comes at a crossroads for the planet's future," Michel Jarraud said, secretary-general of the World Meteorological Organisation (WMO).

Around 50 years ago, scientists set their sights on the greatest-ever investigation into the Arctic and Antarctica.

In those days, polar science was a rugged affair: part research but mostly derring-do, requiring men to pitch muscle and willpower against blood-freezing desolation.

The 1957-8 mission memorably featured the first land crossing of Antarctica, with that great New Zealander, Sir Edmund Hillary, leading the charge with converted Massey Ferguson tractors.

Thousands of scientists from more than 60 countries are to take part in 220 research and outreach projects under IPY, which in fact will last two years, as this is the time it takes to complete a full year of work in both poles.

Gathered under the umbrella of the International Council for Science, the projects will give top priority to studying climate change.

Over the two last decades, Alaska, Siberia and parts of the Antarctic peninsula have been the three fastest-warming regions on the planet, scientists have found.

Canada's native Inuit say their way of life is now in peril. Melting permafrost is wrecking the foundations of homes, while shorter seasons of ice cover and thinner ice make fishing and hunting for seals difficult and dangerous.

In January, the UN's Intergovernmental Panel for Climate Change (IPCC), the top scientific forum on global warming, warned sea ice would shrink in both poles by the end of the century.

The Arctic is being especially affected, for the extent of ice that freezes in summer is retreating steadily, and re-freezing is now being delayed until late autumn.

Since 1978, the extent of Arctic sea ice has been shrinking by 2.7 per cent on average each decade, with the summer ice declining by about 7.4 percent, according to the IPCC.

At the higher end of current greenhouse-gas estimates, large areas of the Arctic Ocean could be ice-free all year round by the end of this century.

The bulk of the world's freshwater is tied up on land in Antarctica and Greenland.

If both icesheets completely disappeared - a catastrophe that almost no-one today considers likely - that would drive up the world's ocean levels by around 77 metres.

By contrast, sea ice, of the kind at the North Pole, floats on the ocean and displaces its own mass, so its melting does not increase sea levels.

The Antarctic icesheet is so far considered stable, although researchers have come across networks of lakes and connection channels under the ice where there have been worryingly fast flows.

The fringes of the Greenland icesheet, though, are being gnawed by unexpected glacier run-off.

"These and other changes in physical and ecological systems of polar regions, all observed over the past two years, indicate a region undergoing rapid change and in need of comprehensive attention," IPY International program director David Carlson said.

The first IPY was in 1882-3, followed by the second in 1932-3.

The third, in 1957-8, was part of the the International Geophysical Year, a golden year for science that unlocked knowledge about glaciology, the aurora, cosmic rays, geomagnetism and the launch of Sputnik, the world's first satellite.

It also had profound political repercussions, leading to the ratification of the Antarctic Treaty in 1961, which enshrined the white continent as a scientific preserve and banned military activity there.

- AFP