Executives from the 40 largest cities plus 17 affiliate municipalities are attending the C40 Large CitiesClimate Summit in Seoul, the third such event since 2005.

Former US president Bill Clinton, whose Clinton Climate Initiative develops programmes to help cities cut greenhouse gas emissions, called for commitments and concrete action at the meeting which ends Thuesday.

The issue of how cities "find a way to continue to thrive and prosper while reducing greenhouse gas emissions is one of the central questions in the whole struggle," Clinton told a press conference.

He said his initiative focuses on creating "communities that can both provide a greater quality of life and generate more clean energy than they use."

Half the world's population lived in cities last year, and that figure is expected to grow to 70% by 2050, said Clinton, citing UN statistics.

They occupy just two percent of the world's land mass yet are responsible for more than two-thirds of global energy use and greenhouse gas emissions.

Mayor David Miller of Toronto, who chairs this year's summit, said he was confident it could find balanced ways to combat climate change.

"We will be able to demonstrate not only how you can fight greenhouse gas emissions but how you can also build green sustainable neighbourhoods, create green jobs and contribute back to the fight against climate change," Miller said.

Seoul Mayor Oh Se-Hoon said the South Korean capital would develop a pilot residential and industrial district that would use 20% less energy than the national average and cut carbon emissions by more than 40%.

Oh said new technologies and renewable energy sources such as photovoltaic, solarand geothermal energy would be used to fulfill the commitment.

London Mayor Boris Johnson said the British capital is committed to reduce its carbon emissions by 60% by 2025, and pointed to retrofitting -- the installation of lagging -- in large numbers of public buildings as key.