Not only are polar regions warming fastest and experiencing some of the earliest effects of climate change, but they are also critical for global climate. For example, conditions at the poles affect how much heat is retained by the earth because of the reflective properties of ice and snow, the world's ocean circulation depends on sinking in polar regions, and melting of the Antarctic and Greenland ice sheets could have drastic effects on sea level. Extracting ice cores also provides valuable information about past climate.

"The change of phase from snow and ice to water is the biggest tipping point in the Earth's system and so, although International Polar Year covers a huge range of science, for me the big issue is climate change and the impact that it's having here," said Chris Rapley, director of the British Antarctic Survey, in a video message from Antarctica. "Over the next two years, I'm looking forward to major progress on key issues such as 'How are the ice sheets responding?' and the trillion dollar question from the point of view of sea-level rise, 'How much, how quickly?'"

Many of the larger International Polar Year projects will enable the collation of data that is only possible to achieve if countries pool their capabilities. And the year will create sophisticated polar observation systems that will still be available for use when International Polar Year itself is over. These include an integrated Arctic Ocean observing system; a southern hemisphere observing system; links between providers of bipolar satellite data; acoustic networks around both poles to monitor the movement of marine mammals and fish; a set of permafrost measurements in boreholes; and a network of local observation sites that engage some of the Arctic's 4 million residents.

"International Polar Year has allowed the international community to talk to each other, build relations and pool resources internationally," said Martin Siegert of the University of Edinburgh, speaking at the UK launch of International Polar Year.

Thirty-three national committees are co-ordinating initiatives for International Polar Year. The year has six scientific themes: status, an investigation of the current polar environment; change, which looks at past and present environmental and social change in order to improve projections of the future; global linkages, which examines the interactions between polar regions and elsewhere; new frontiers, a programme to address scientific challenges such as understanding polar ecosystems and exploring regions beneath polar ice sheets; vantage point, which uses the poles for observing space; and the human dimension, a group of projects looking at the sustainability of circumpolar human societies.

The last International Polar Year - also known as International Geophysical Year - was in 1957-58. There were also polar years in 1882-3 and 1932-3.

"The last time - in International Geophysical Year - we really didn't know much about Antarctica," said Siegert. "We still know very little about Antarctica and the Arctic but we now know it's very important."

This International Polar Year will contain a significant amount of exploration work to find out more about the regions.

International Polar Year is sponsored by the International Council for Science and the World Meteorological Organization.