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British Prime Minister Gordon Brown was to warn representatives of the world's biggest carbon polluters Monday of a climate catastrophe if they do not strike a deal at the Copenhagen summit.
Brown was due to address the Major Economies Forum meeting in London with a message that they must find a way to "break the impasse" on getting a far-reaching agreement at the United Nations climate conference in December.
The 17 powers that make up the MEF, along with developing nations and UN representatives, are trying to iron out some of their differences before the crunch summit in Denmark.
"In every era there are only one or two moments when nations come together and reach agreements that make history -- because they change the course of history," Brown was to say, according to extracts from his speech released by his Downing Street office.
"If we do not reach a deal at this time, let us be in no doubt: once the damage from unchecked emissions growth is done, no retrospective global agreement, in some future period, can undo that choice. By then it will be irretrievably too late."
The MEF was launched by US President Barack Obama earlier this year on the back of an initiative by his predecessor, George W. Bush, to speed up the search for common ground among the most polluting world economies.
It then intends to hand this consensus for approval by the UN Framework Convention on Climate Change, the sprawling 192-nation global arena.
The December 7-18 UN climate summit in the Danish capital will see nations attempt to hammer out a new global climate treaty to replace the Kyoto Protocol, which expires in 2012.
Brown was to say he thought a deal at Copenhagen is possible, but negotiators are not moving fast enough.
Instead, "leaders must engage directly to break the impasse. We cannot compromise with the Earth," he was to say.
"We can not compromise with the catastrophe of unchecked climate change; so we must compromise with one another.
"We cannot afford to fail... This is the moment. Now is the time. For the planet there is no Plan B."
The MEF comprises Australia, Brazil, Canada, China, the European Union, France, Germany, India, Indonesia, Italy, Japan, South Korea, Mexico, Russia, South Africa, Britain, and United States.
The MEF countries represent about 90 percent of global emissions.
The London talks are focusing on emissions cuts, the protection of forests and climate finance -- Brown has said 100 billion dollars a year is needed to help developing countries tackle climate change.
India said last month it was ready to set itself non-binding targets for cutting carbon emissions, while China said it would curb the growth of its emissions by a "notable margin" by 2020, although it did not specify further.
The US special envoy for climate change, Todd Stern, told British television on Saturday that developing economies must boost their efforts, warning it was "certainly possible" that no deal would be agreed in Copenhagen.
"What we need to have happen is for China and India and Brazil and South Africa and others to be willing to take what they're doing, boost it up some, and then be willing to put it into an international agreement," he said.
But climate campaigners Friends of the Earth said it was up to the rich countries in the MEF to "face up to their legal and moral responsibility by agreeing to cut their emissions first and fastest".
