By Richard Black
Environment correspondent, BBC News website
Ed Miliband says there is no "Plan B" on reaching agreement
Agreeing a new global climate treaty looks more "do-able" after London talks between the big-emitting nations, UK Climate Secretary Ed Miliband has said.
Talks between 17 countries producing about 80% of global emissions ended with a call for more funds to help poor nations adapt to climate change.
The US president may attend December's UN summit if enough progress has been made by then, said US envoy Todd Stern.
Mr Miliband said he would be going "all out" for an agreement in Copenhagen.
Earlier in the day, UK Prime Minister Gordon Brown warned that "catastrophe" lay ahead if climate change were not tackled.
The two days of talks under the auspices of the Major Economies Forum (MEF) were not designed to bring new pledges, but to facilitate dialogue in a less pressured environment than the formal UN negotiations.
"It's an uphill battle, but I just feel today it's more do-able than (I did) yesterday," Mr Miliband told journalists in a briefing directly after the MEF meeting closed on Monday evening in London.
"There was a universal view that we need to get an agreement in Copenhagen - not an agreement at any price, but that we've come a long way and we intend to translate that into an agreement by the end of the year."
In recent weeks, there have signs that a deal might be impossible to secure in December, with important details potentially being left for discussion next year.
But Mr Miliband said he was "going all out" for agreement at Copenhagen, and there was no "Plan B".
He also declared that "leaders need to be involved".
Ministers and negotiators cannot do the job alone, he said.
Many observers believe that Barack Obama is the leader whose presence would do most to hasten a deal, but Mr Stern, the US administration's chief negotiator, said the president's attendance was not decided.
"We are not writing anything off or foreclosing possibilities," Mr Stern said.
"If the kind of progress is made that would warrant the attendance of leaders, we'll certainly look at that."
Environment groups urged leaders including Mr Obama to step up their level of personal commitment.
Todd Stern described Gordon Brown as "inspirational" on climate
"The planet cannot afford the US administration downplaying the significance of the Copenhagen climate summit," said Martin Kaiser, climate policy adviser with Greenpeace International.
"President Obama and other world leaders need to go to Copenhagen and take personal responsibility for its success, in order to achieve an agreement to avert catastrophic climate change."
Mr Stern also told reporters that a new treaty could not be an extension of the Kyoto Protocol, as many developing countries are demanding, if the US is to join up.
"We're not a party to the Kyoto Protocol and we're not going to be a party," he said.
The two days of talks at London's Lancaster House focused on providing finance to assist developing countries prepare for and adapt to impacts of climate change, and to protect forests.
Six developing countries, including some considered to be in particular need of financial assistance in adapting to climate impacts, such as Ethiopia and The Maldives, were invited to an MEF meeting for the first time.
The final communique makes it clear that discussions focused on mechanisms for raising, governing and disbursing funds.
But there was also a clear commitment that richer countries would have to provide some money from the public purse, and that the scale of the funds on offer would need to be "scaled up".
The EU is due to finalise its proposals on financing adaptation shortly.
The MEF communique also asks the forthcoming G20 finance ministers' meeting in St Andrews, Scotland, to "advance these discussions".
The final week of formal preparatory negotiations within the UN process leading up to the Copenhagen summit begins in Barcelona in just under a fortnight.