World leadersshould take action on climate change, the American Association for the Advancement of Science said on Sunday.

"We are already experiencing global climate change. It is time to muster the political will for concerted action," the association's board said in its firstconsensus statement on the issue, released at the group's annual meeting in San Francisco.

"The time to control greenhouse gas emissions is now" because waiting to address climate change will be harder and more expensive, the group said.

The association is calling forresearch to"transform the existing and future energy systems of the world away from technologies that emit greenhouse gases."

The group, the largest general science society in the world, said the concentration of carbon dioxide in the atmosphere is now higher than at any time in 650,000 years, and the average temperature on Earth isheading for levels not experienced for millions of years.

Predicted problems caused by warming, such as droughts, heat waves, floods, wildfires and severe storms "are early warning signs of even more devastating damage to come, some of which will be irreversible."

The association said the problems are worse in the Far North, a conclusion that Canadian scientists and politicians have also reached.

In Shishmaref, Alaska, retreatingsea ice and the rising level of the Arctic Ocean are driving the 600 residents from thevillage, and destroying their way of life.

Arcticchanges like 'coal miner's canary'

Regions around the Arctic "are like the coal miner's canary, the early warning to the rest of us of the extent to which the Earth's climate is changing," association president John Holdren said in a release.

A majority of Americans agree that global warming is real, but are not sure how serious it is, surveys taken byJon Krosnick, a Stanford University professor of communication and political science, show.

Because themedia has covered thestory in a "balanced" way, the small minority of scientists who doubt global warming get equal play to that of the 99 per cent who believe the problem is serious,Krosnick said Sunday.

A report by Krosnick was released at the association's meeting.