(Bloomberg News) New York Mayor Michael Bloomberg is leading an effort by 58 of the world's largest cities to reduce greenhouse-gas emissions while federal governments struggle to meet global targets following two decades of discussions.

The member-cities of the C40 Cities Climate Leadership Group produce about 14 percent of the world's greenhouse-gas emissions. Their actions to improve energy efficiency and invest in renewable power will reduce emissions by 248 million metric tons in 2020, Bloomberg said on a conference call. The cities can cut emissions by more than 1 billion tons by 2030, or the equivalent annual output from Mexico and Canada.

Mayors, who have oversight of agencies responsible for more than three quarters of urban emissions, may be able to implement policies faster than federal governments, former U.S. President Bill Clinton said on the call. Cities that enact new rules and regulations and share their findings may help nations meet global environmental targets, such as reducing methane emissions from landfills, one of the most potent greenhouse gases.

"We can buy the world another 10 to 20 years from the worst effects of global warming if we go after methane," Clinton said on the call. "It will improve the quality of life for everyone."

Cities including Hong Kong, Sydney, Los Angeles and New York have undertaken more than 5,000 actions to cut emissions since the C40 was formed in 2005. Today they are starting an effort to share methods of reducing methane from landfills with support from the World Bank and the U.S. State Department.

"Life expectancy in New York City is now three years longer than the national average," Bloomberg said. "There's no question that if you clean the air and clean the water, it improves lives."

Rio Conference

The C40 mayors are meeting today in Rio de Janeiro to urge world leaders to pursue sustainability initiatives at the Rio+20 conference, where delegates from 190 nations will discuss steps to eradicate poverty while stemming environmental degradation.

Clinton chastised world leaders for failing to enact policies to curb climate change, sometimes because environmental goals are hindered by the political process. Mayors have fewer barriers to enacting sustainability policies, and are leading by example, he said. "The power of example is more powerful than a speech by a head of state."

The mayor is founder and majority owner of Bloomberg News's parent, Bloomberg LP.