By Richard Black
Environment correspondent, BBC News website
David Miliband, Bernard Kouchner and Carl Bildt aim to push the talks forward
Prospects for reaching a new global deal on climate change are "in the balance", according to UK Foreign Secretary David Miliband.
There is a "real chance" that December's UN summit in Copenhagen will not reach agreement, he said.
Mr Miliband was briefing reporters prior to a whirlwind tour of European capitals aimed at stepping up EU diplomacy on the Copenhagen process.
The EU could be a "force multiplier" on the issue, he said.
In the same news conference, Mr Miliband's younger brother Ed - the UK Energy and Climate Secretary - said the Copenhagen process was too important to be a matter for politicians only.
On a recent visit to Bangladesh, he related, he had seen how "two million people living on sandbanks are already living with the effect of climate change, with more flooding than usual".
Whether Copenhagen produced money to help countries such as Bangladesh adapt to climate impacts would, he said, be "a big determinant of their survival".
Preparations for a new UN climate treaty to supplant the Kyoto Protocol began nearly two years ago, but in recent months it has become clear that wide divisions remain between various blocs.
Developing countries say that as the industrialised west grew rich through intensive fossil fuel use, emitting carbon dioxide in the process, western countries bear historical responsibility for climate change and must take the lead in cutting emissions.
So far, the scale of cuts pledged by western leaders has not met the expectations of the developing world.
Neither have the sums of money coming forward to help poorest nations protect their societies and economies against climate impacts.
This means in turn that developing countries have been unwilling to pledge measures to restrain the growth in their own emissions.
"The deal that the world needs in Copenhagen is in the balance," observed David Miliband.
The foreign secretary described the news that Japan's incoming government would triple the size of its emission cut pledge as "very significant".
The UK government sees itself as a leading player in international climate diplomacy. In June, Prime Minister Gordon Brown proposed setting up a fund to raise and disburse $100bn (£60bn) annually for climate protection and adaptation.
David Miliband's tour of EU capitals is aimed at increasing and co-ordinating diplomatic efforts towards securing a Copenhagen deal, including promoting the adaptation fund.
Much of the negotiating, he said, would have to be done in the months leading up to the UN summit; and the EU, because of the influence it had in various countries, could be an effective leader in that.
An agreement with Mr Miliband's French and Swedish counterparts, Bernard Kouchner and Carl Bildt, means that diplomatic missions of the three countries will step up lobbying across the world in the coming weeks - a period that also sees a special climate change event for heads of government at the UN in New York, and a key meeting of the G20 in Pittsburgh that may come up with new initiatives on funding.
If none of this worked well enough, the foreign secretary conceded: "There is a real danger that the talks scheduled for December will not reach an agreement".
This is the strongest admission yet from a senior UK minister that a deal is not necessarily in the bag; and with only three months left until the summit, environmental organisations agreed that the pace and intensity of diplomacy needed to be stepped up.
"[David] Miliband's acknowledgement that the EU must harness political will right now, in order to make a sustainable future a possibility, is very welcome," said David Norman, head of campaigns at WWF UK.
"Copenhagen is fast approaching, and high level discussions over the next few weeks will determine whether we can achieve a decent global deal in December or if we will shackle ourselves to a future of runaway climate change."