The five Arctic nations said on Thursday that climate change has become the biggest threat to polar bears, according to reports reaching?in Stockholm?from Oslo.

The impacts of climate change and the continued and increasing loss and fragmentation of sea ice constitute the most outstanding threat to polar bear conservation, the countries, namely Canada, Denmark, Norway, Russia and the United States, said in a joint statement after a three-day meeting in Tromsoe, a northern city of Norway.

Long-term conservation of polar bears depends upon successful mitigation of climate change, they noted.

The world's polar bear population, estimated between 20,000 and 25,000, will shrink by 60 percent by 2050 if no action is taken, some Norwegian researchers said.

The five Arctic nations also agreed to prepare national action plans to protect the polar bears and their habitat, and to coordinate research.

They will meet again in 2011 in Canada, followed by another meeting in Russia in 2013, according to the joint statement.

Around 1970, widespread hunting had reduced polar bear populations in many parts of the Arctic. At that time hunting was considered the only real threat to the animal.

The five Arctic nations entered into an agreement in 1973 to protect polar bears and their habitat. The five Contracting Parties met last time in Oslo 1981 and decided then that the agreement would be valid indefinitely.

(Xinhua News Agency March 20, 2009)