The five-billion-dollar proposal, unveiled by former US president Bill Clinton and mayors from cities around the world, would involve slashing energy consumption in existing city buildings through improved technology.

Livingstone, one of the major drivers behind the plan, said the program could cut worldwide greenhouse gas emissions by one tenth over the next decade, based on extrapolations of initial savings.

"If we look at the pattern of carbon emissions around the world, in the decade that follows this decision, as this new global industry takes off, we can reduce total global carbon emissions by about 10 percent," he said.

The so-called energy efficiency building retrofit program brings together Clinton's private foundation, four of the largest energy service companies, five of the world's biggest banks and cities from four continents.

"This is not just an initiative, this is the biggest single step to tackle climate change that has been taken by any layers of government anywhere in the world since the debate about climate change started," Livingstone said.

Clinton said that the proposal would help owners of older buildings that leak hot air in the winter and cool air in the summer to slash between 25 and 50 percent off their current energy usage.

"Cities use more than 75 percent of the world's energy and generate more than 75 percent of its greenhouse gases. Buildings are often the largest energy users," he said.

"If all buildings were as efficient as they could be, we'd be saving an enormous amount of energy and significantly reducing carbon emissions."

Livingstone said he hoped the initiative would help national leaders to improve their commitment to tackling climate change.

"We in the cities couldn't wait. We see the problems, we see the damage that carbon emissions are doing, the threat of flooding and the violent weather and terrible levels of heat," he said.

New York Mayor Michael Bloomberg, who has already committed his city to cut greenhouse gas emissions by 30 percent before 2030, described the initiative as a major contribution to fighting global warming.

"It really is groundbreaking. It really is going to make a difference," he said.

"Today, major businesses and financial institutions increasingly understand that shrinking the world's carbon footprint is a pro-growth strategy, indeed the only pro-growth strategy for the long term," he said.

The program would provide funding for cities and private building owners alike to introduce modern energy-saving solutions, from using more efficient light bulbs to introducing better insulation and heating systems.

The energy savings are expected eventually to offset the costs of the program, the mayors said, without specifying a timeframe.

The cities involved in the initiative include Bangkok, Berlin, Chicago, Houston, Johannesburg, Karachi, London, Melbourne, Mexico City, Mumbai, New York, Rome, Sao Paulo, Seoul, Tokyo and Toronto.

Wednesday's announcement came towards the end of a four-day summit of mayors and business leaders from more than 40 of the world's biggest and most polluted cities aimed at tackling climate change and improving the environment.

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