Public awareness about the "catastrophe" of climate change is not high enough to pressure politicians into taking action, according to former Vice President Al Gore.

Mr Gore, who shared a Nobel Prize in 2007 for his environmental campaigning, said politicians will only do more once the people who elect them force the issue.

Voters need to tell leaders they must act on environmental concerns if countries are to strike a new deal on global warming at UN climate talks in Denmark later this year.

"The only way we can get one is if politicians in each country act fast and the only way that can happen in turn is if awareness rises to the level to make them feel it is a necessity," Mr Gore said in a speech. "We can berate politicians for not doing enough and for compromising too much and for not being bold in addressing this existential threat to civilisation.

"But the reason that they don't is because the level of awareness and concern among populations still has not risen to cross the threshold that makes the political leaders feel they must address it."