Leaders from more than 30 of the world's largest cities are in New York Tuesday to discuss combating carbon emissions and reversing climate change. Victoria Cavaliere reports from York that former U.S. President Bill Clinton and New York City Mayor Michael Bloomberg are co-sponsors of the C-40 Large Cities Climate Summit.

At the conference, municipal leaders from New Delhi, India, to Johannesburg,South Africa, to Bangkok, Thailand are sharing ideas on how to fight global warming and reduce greenhouse gas emissions.

London Mayor Ken Livingston introduced the city's so-called "congestion tax" in 2003. Now, most vehicles entering the center of London Monday through Friday are charged $10. Livingston says the plan was immediately successful. Londoners took to the buses and also to their bikes, and congestion decreased by over 20 percent.

"That has led to 20 percent carbon-dioxide reduction emissions inside the central zone, reductions in nitrous oxides in particular by 10 percent," said Ken Livingston. "Therefore, we looked to extend it."

In February of this year, London doubled the size of its congestion-tax zone. To keep up with increased need for public transport, the city has massively expanded its bus service.

Livingston says congestion taxes have also been successful in Singapore and Stockholm. New York City is currently considering its own version of such a tax.

Carlos "Beto" Richa, the mayor of Curitiba, in southern Brazil, has also taken bold steps to decrease pollution and improve public transportation in his city.

Richa says significantly cutting the cost of fares on buses and trains has increased passenger rides by 12 million in one year. In turn, emission levels fell 12 percent.

"In emerging countries, ensuring quality mass transit assistance is not enough," he said. "Offering fair prices, compatible with the users' wallet, is essential."

The plans were controversial at first, but both mayors say their popularity rose as they adopted a green agenda. Livingston says elected officials should not be afraid of criticism for trying to tackle congestion issues.

"You can't do this in isolation," he said. "You have to make certain that for the people giving up the car, whether they wish to or not, there is a relatively cheap public transport system available."

Both mayors say their green policies have also translated into positive economic trends. Richa says his transportation policies are paying for themselves. Livingston says his green agenda has kept employers in the city center and contributed to London's economic upswing.