Leaders of nearly 40 of the world's largest cities are gathering in New York to exchange ideas on combating global warming. VOA correspondent Peter Heinlein reports former U.S. President Bill Clinton and New York Mayor Michael Bloomberg are co-hosting the C-40 Climate Change Conference.

The New York gathering is the second of its kind. The first, in London two years ago, drew representatives of 18 large cities.

London Mayor Ken Livingstone is chairing this week's event. He is calling on local leaders to act, because they are closer to "clean air" issues than national governments.

Among the ideas being discussed is New York Mayor Bloomberg's "congestion pricing" proposal. The idea is to charge drivers coming in to midtown Manhattan between six a.m. and six p.m. Bloomberg and supporters of the idea say fewer cars would mean cleaner air, but critics say it would penalize commuters who cannot afford to live in the inner city.

Bloomberg admitted the plan faces an uphill fight, but said he would continue to push for the adoption of an eight-dollar per car fee. "If we don't do it now, we're not going to get it done," he said.

London already has a congestion tax, and London's deputy mayor Nicky Gavron says it has changed the city's character. "All sorts of people are walking more, cycling more, and the look and feel of London's streets is better, and of course the air quality is so much better," he said.

Mayor's from many of the world's largest cities are attending the conference, including those from Copenhagen, Bangkok, Tokyo, New Delhi, Mumbai, Karachi and Mexico City.

The mayor of Los Angeles, Antonio Villaraigosa is planning to announce that his city, the second largest in the United States, will begin it's own carbon reduction plan.

Scientists are increasingly concerned about the amount big cities contribute to emissions of heat-trapping greenhouse gas emissions, including methane and carbon dioxide. In cities such as New York, buildings contribute a significant amount to emissions through use of electricity, natural gas and fuel oil.