European leaders claimed a climate change breakthrough yesterday after persuading the United States and other sceptics to agree for the first time to adopt a target for reducing carbon emissions.

Gordon Brown hailed “major progress” and said that leaders had signed up to a series of practical measures to reduce dependence on fuel. He predicted that in Britain electric cars could become the norm one day.

Despite disappointment among environmental groups and some nations that the summit had not gone farther, Mr Brown said that counties that had once rejected international targets had now accepted them. The G8, which said only last year that it would seriously consider a 50 per cent reduction in emissions by 2050, agreed yesterday that it would aim for at least 50 per cent and that it would consider and adopt the target.

Critics swiftly pointed out that the summit had failed to agree on a target for cuts by 2020 with neither President Bush nor Yasuo Fukuda, the Japanese Prime Minister, willing to be bound by a medium-term agreement.

The target agreement comes before a UN summit next year in Copenhagen to find a replacement for the Kyoto Protocol, which expires in 2012. The summit persuaded the World Bank to redirect funds so that $150 billion (£75 billion) was spent in developing countries in the next three years to help them to change to cleaner technologies.

Mr Brown said that Britain's target to reduce new car emissions would inevitably lead to the day of the hybrid, electric and battery-powered car. The electric car could become the family car, and even electric sports cars were in development.

He told reporters that clean cars would be exempt from car tax - and suggested that high oil prices could prove “to the benefit of car drivers” by pushing forward alternatives. “These hybrid cars, as we are finding with discussions in America and Japan, are cars within the range for families - not just for a few but cars that the ordinary family would think of buying.”

The G8 also agreed a list of 25 areas where more prosperous countries could help by cutting energy use - including abandoning traditional light bulbs and cutting power used by appliances on standby.

The energy efficiency standards will be drawn up by an energy conference in Japan in the coming months and then fed into a meeting of oil producers and consumers being hosted by Mr Brown in London, which he said would take place in December, before being put in the hands of a permanent international body.

Yesterday's statement addressed total world emissions rather than just those produced by wealthy countries, and critics attacked it for failing to go much beyond the G8 statement last year. The communiqué also did not set a base year from which emissions would be cut.

“So little progress after a whole year of minister meetings and negotiations is not only a wasted opportunity, it falls dangerously short of what is needed to protect people and nature from climate change,” said Kim Carstensen, the director of WWF Global Climate Initiative.

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