"The Arctic and the world cannot wait any longer," environment ministers from the five nations said in a joint statement after talks in Oslo. The five all have Arctic territories.

"The climate is hurtling towards a turning point after which irreversible processes will have been set in motion," they said of the Arctic thaw.

They noted the ice on the Arctic Ocean shrank in September to 4.13 million sq km (1.6 million sq miles), the smallest since satellite records began in 1979 and far eclipsing the low in 2005. The ice extent is now expanding as winter approaches.

The melt, blamed by the UN climate panel on heat-trapping gases emitted by burning fossil fuels, threatens the livelihoods of indigenous hunting peoples and wildlife such as polar bears and seals.

Swedish Environment Minister Andreas Carlgren said the thaw of the Arctic ice might already have reached a point of no return. "We may have passed the tipping point," he said.

Many climate scientists say the Arctic is warming about twice as fast as the rest of the globe because dark ground and water, once uncovered, soaks up more heat than white ice and snow.

The Nordic nations said a meeting of environment ministers meeting in Bali, Indonesia, in December should agree "tangible measures to reduce emissions of greenhouse gases".

The Bali talks are meant to launch two-year negotiations on a new climate pact to succeed the Kyoto Protocol with a goal of sealing a deal at a UN conference in Copenhagen in late 2009.

Norway, the world's number five oil exporter, defended itself from criticism that its main industry is at odds with its drive for environmental protection. "We have a special responsibility to be at the technological forefront" in curbing pollution from oil, Norwegian Environment Minister Erik Solheim said. He also promised a "maximum effort" to develop cleaner technologies such as wind and solar power.

The ministers said the shrinking of the ice was one of the most visible signs of climate change and could help focus attention on other changes such as heatwaves, rising seas or floods.