Mayors vaunt progress against climate change

The world's mayors say they are taking real, measurable action to slow global warming, even as national governments struggle to define the goals of the upcoming Rio earth summit.

New York Mayor Michael Bloomberg says the C40 grouping of 58 megacities around the globe has already undertaken nearly 5,000 initiatives to fight global warming. Those efforts could reduce greenhouse gas emissions by over a billion tons by 2030. That's the equivalent of the combined annual emissions of Mexico and Canada.

Bloomberg, who chairs the C40, was speaking Tuesday the group's meeting in Rio de Janeiro on the eve of the Rio+20, the United Nations' conference on sustainable development.

Amid squabbling between nations, negotiations over the Rio+20's final statement have dragged on. Environmental groups have criticized the document as toothless.