Gordon Brown: "An ambitious agreement at Copenhagen is achievable"
Prime Minister Gordon Brown wants to set up a £60bn annual fund to help poor countries deal with climate change.
He hopes it will break the deadlock over who will pay developing nations to adapt to the changing climate and who will help them obtain clean technology.
Countries must reach a binding global agreement on carbon emission cuts at December's Copenhagen summit, he said.
The summit is seen as the last chance to negotiate a successor to the Kyoto agreement, which expires in 2012.
Environment and anti-poverty campaigners welcomed Mr Brown's remarks but said he and other leaders must deliver real financial support not merely "empty rhetoric".
Finance is one of the key sticking points in global negotiations, with poor nations demanding huge amounts of cash and rich nations reluctant to commit.
The UK figure is less than developing nations say they need - but at least it will provide a negotiating point in the coming G8 when the leaders of emerging nations will join for a special climate summit chaired by US President Barack Obama.
Some of the political blocks need to be cleared in this meeting if there is to be a new global deal at the UN climate talks in Copenhagen in December.
Mr Brown said: "Copenhagen is twenty-three weeks away. When historians look back on this critical moment, let them say, not that we were the generation that failed our children; but that we had the courage, and the will, to succeed."
'Act with vision'
Speaking in London, Mr Brown said leading industrialised economies must support developing nations most at risk from climate change to enable them to keep on growing while meeting their environmental obligations.
He suggested £60bn would be needed to help poor countries adjust to climate change, stressing the UK would pay "its fair share" towards this.
"Over recent years, the world has woken to the reality of climate change," he said.
"But the fact that is that we have not yet joined together to act against it.
"Copenhagen must be the moment we do so.
"If we act now, act together and act with vision and resolve, success at Copenhagen is within reach."
Money could be raised from selling carbon permits and from existing development aid budgets, although he said contributions from the latter should be limited.
The BBC's Environment Analyst Roger Harrabin said Mr Brown's efforts were designed to break the deadlock over who would pay for poorer countries to make the difficult transition to a low-carbon economy.
But Oxfam said at least $150bn a year was needed to protect poorer countries from climate change.
"The prime minister's proposal could give a welcome kick-start to negotiations if other leaders rise to the challenge," said chief executive Barbara Stocking.
"Ultimately, if catastrophe is to be avoided and the poorest people protected, we need more money and sooner."
Friends of the Earth said it welcomed the government's "recognition that finance is key to breaking the deadlock in the stalled UN talks," but added: "We have no chance of achieving the cuts required through the con of carbon offsetting."
By putting a figure on the cost of climate change adjustment, Greenpeace said Gordon Brown was showing leadership but urged him to put "serious money" on the table when G8 leaders meet in Italy next month.
Lord Stern, who wrote a climate change report for the government in 2008, said Mr Brown's initiative was "timely" but countries getting money should be able to follow their own development agendas and not have them imposed.
The UK government is committed to cutting greenhouse gas emissions by 80% by 2050 and argues the rest of the world must follow suit if global temperature rises are to be restricted to 2 Celsius - above which is regarded dangerous.
"We cannot in good conscience plan for the world to exceed that limit," Mr Brown said.
Ministers say the legally-binding target puts the UK in the vanguard of international efforts on climate change.
But the Lib Dems said the UK's targets were not ambitious enough and its green credentials were undermined by the government's approval of new coal-fired power stations and airport runways.
"People in the UK and around the world should do all they can to tackle climate change, but we need the government to lead by example," said the party's climate spokesman Simon Hughes.
"Ministers should push for tougher targets that follow the science and not the politics."