"The politics is moving more slowly than the science or the economics globally. We have got to inject new momentum into the politics," he told the Environment Agency's annual conference.

"The next year is absolutely key."

He highlighted the German presidency of the European Union and the Group of Eight (G8) rich nations, a new Congress in the United States and a new UN secretary-general as important for how 2007 would turn out environmentally.

"If there is a gap after 2012 ... the carbon market ... will collapse. To avoid that you basically have to start negotiations in a year's time," he said.

The Nairobi meeting agreed that talks on taking forward and expanding Kyoto should get underway in 2008 but some delegates criticised a lack of firm action on global warming.

Scientists predict that unless firm action is taken to curtail emission of greenhouse gases like carbon dioxide from burning fossil fuels, global temperatures will rise by between two and six degrees Celsius by the end of the century.

The United States, which pulled out of Kyoto in 2001, argues that such action could cripple its economy.

A report last month by former World Bank chief economist Nicholas Stern said that while action now to curb carbon emissions would cost some one percent of world economic output, delay could push the price up to 20 percent.

Alex Bowen, the Stern group's senior economic advisor, told the meeting that business as usual would ensure that world temperatures rose by at least five degrees by 2100, bringing climatic, economic and social catastrophe to the world with floods, famines and wholesale species' wipeout.

"International collective action is necessary. We need an agreed sense of where the world is heading," he said.

Oxford University academic Dieter Helm, head of an academic panel advising Miliband's ministry on policy, said he believed the Stern report had underestimated the scale of the problem.

"This is an enormous challenge. The chances of sustaining the world economy based upon the current levels of consumption-led growth and the population growth that we are looking at ... are quite shallow," he said.