Environmental groups said the agreement at the G8 summit in Japan did not go far enough, and the search for a deal moves to the talks about a "son of Kyoto" global agreement in Copenhagen next year.
George Bush, who had previously stalled progress by agreeing only to "seriously consider" a 50 per cent cut, finally gave a little ground yesterday, knowing his two possible successors as US President, Barack Obama and John McCain, were ready to go further.
However, the G8 leaders failed to agree on an interim target to cut emissions by 2020 or the start date from which the 50 per cent cut would be measured.
Five big emerging countries - China, India, Brazil, Mexico and South Africa - will urge G8 leaders today to agree to reduce their emissions by 80 to 95 per cent by 2050, and to set a medium-term target of a 25 to 40 per cent cut below 1990 levels by 2020. G8 leaders acknowledged the need for interim goals but officials said they would not be agreed until next year's talks.
G8 leaders approved a $150bn (£75bn) plan to help developing countries "go green" to make them more likely to meet the proposed global target. The aim is to stop them building coal and oil-fired power stations and reduce deforestation.
The summit also backed 25 measures to encourage householders and business to help save the planet, saying the blueprint could cut 20 per cent of the world's energy consumption - the amount currently soaked up by America.
Gordon Brown, who pressed the proposals, outlined his vision of a "green" Britain in which all new family cars could be electrically powered by 2020. He is urging the European Union to agree a 60 per cent improvement in fuel efficiency by then. In the short term, the Government will launch an "eco-driving" campaign to tell drivers about accelerating, braking and tyre pressures.
The measures, which could eventually become worldwide, include mandatory "stand-by" consumption of one watt for electrical appliances; targets to cut energy consumption from new buildings and an end to traditional lightbulbs, which are already being phased out in Britain by 2011.
Mr Brown said the oil price rise had made the need to combat global warming more urgent. "There has been major progress on the climate change agenda, beyond which people would have thought possible a few months ago," he said. "It is a big shift."
Green groups said the G8 leaders had missed a golden opportunity. "It is pathetic that they still duck their historic responsibility," WWF said. "The G8 nations are responsible for 62 per cent of the carbon dioxide accumulated in the earth's atmosphere, which makes them the main culprit of climate change and the biggest part of the problem."
John Sauven, executive director of Greenpeace, accused them of "vacuous back-slapping." He said: "They have failed the world again. We needed tough targets for the richest countries to slash emissions in the next 100 months, but instead we got ambiguous long-term targets for the world in general."
Friends of the Earth criticised the decision to channel some of its "climate investment funds" for developing countries through the World Bank, saying it was a "fossil fuel financier and major deforester".
A spokeswoman said: "G8 leaders have left the fox to guard the hen house."
© 2008 The Independent