Oslo  - Threats to polar bear populations, mainly due to climate change, were the topic of a three-day meeting that opened Tuesday in the northern Norwegian city of Tromso.

"Climate change has superceded hunting as the main threat to polar bears. We have to act to protect the habitat of the polar bear," Norwegian Environment Minister Erik Solheim said in his opening remarks.

"Global warming has to be stopped if we are to succeed," he added.

Melting Arctic sea ice poses a threat to polar bears that raise their young and hunt for food off the sea ice.

Some researchers fear the polar bear population will shrink by a tird withion a few decades if the trend is not reversed.

Norway had hoped the meeting would be held with attendance of conservation groups including WWF, but the deliberations were to be held behind closed doors with the exception of discussions on some scientific data.

"This is not part of Norwegian political tradition or my wishes," Solheim told reporters.

Norway, Denmark/Greenland, Russia, the United States and Canada signed the 1973 polar bear agreement to protect polar bears and their habitat.

The five countries agreed in 1981 to extend the treaty indefinitely, but have not held regular meetings. (dpa)