The climate deal planned for Copenhagen in 10 weeks' time is in grave danger of failure, the prime minister has said.
Gordon Brown has become the first world leader to offer to go to the Danish capital to help seal the deal.
He told Newsweek magazine there was no second chance to undo "catastrophic damage" to the environment if "we miss the opportunity to protect the planet".
This year's talks are vital as they aim to produce a successor to the Kyoto Climate Protocol on global warming.
Mr Brown also warned that consumers would have to pay more for energy in the future, whether the UK opts for high or low carbon energy sources.
The annual climate negotiations are normally done by environment ministers, but they lack the political muscle to make the big spending decisions which underpin the talks.
The vast majority of climate scientists say there must be no further delay in emissions cuts.
Mr Brown said a deal was also essential to help kick-start a global low-carbon economy as a route out of recession.
What has now become clear is that the push toward decarbonisation will be one of the major drivers of global and national economic growth over the next decade," he said.
"And the economies which embrace the green revolution earliest will reap the greatest economic rewards."
Mr Brown said, if necessary, he would go to Copenhagen himself, and his staff said he would urge other leaders to follow suit at the UN this week.
It's almost inconceivable that this sort of initiative will not be necessary.
Mr Brown also said clean energy investment would put up costs for consumers - but by less than would happen if the UK stuck with fossil fuels.
The costs will be affordable as the economy grows and as energy efficiency improves, he says.
He is following a lead set by Energy Secretary Ed Miliband, who was first to break with the political spin that it was possible to decarbonise the economy without putting up prices.
Some will be sceptical about Mr Brown's comments on green investment.
Britain's leaders have been promising a green economy for many years but Germany, Denmark, the US - and now increasingly China and India - are taking a market lead.
Mr Brown's cash give-away for old cars did not include any environmental conditions.
Critics will also point out that as chancellor, Mr Brown blocked many green policies, and some may question this latest initiative.
But he has already taken an international lead by suggesting rich nations should pay $100bn (£62bn) a year to help poor nations with the changing climate.
This helped kick-start the EU into a position more acceptable to developing nations.
Greenpeace welcomed the prime minister's initiative to go to Copenhagen.
Director John Sauven said: "Gordon Brown has injected a note of urgency into the Copenhagen talks by agreeing to attend. At the moment there is a huge gap between what needs to be done and what world leaders are promising to do."
But for all Mr Brown's promise of leadership, the UK has not yet committed to the 40% CO2 cuts most scientists say are needed from rich nations by 2020 to contain climate change.
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