MEXICO CITY – Global megacities such as Mexico City, Seoul, Paris and Los Angeles are more populous than scores of countries, and devour huge amounts of energy, but they’ve carried no weight in United Nations climate change talks.

Until now.

Next week, when envoys come together in Cancun for a follow-up session to last year’s rancorous U.N. climate talks in Copenhagen, Mexico City’s mayor will be on hand to trumpet how the world’s great cities are finding ways to reduce the greenhouse gas emissions blamed for higher global temperatures.

Few expect the Cancun meeting to make progress toward an agreement on emissions reductions, which scientists say are critical to heading off extreme weather, crop failures and rising sea levels. But as nations dither, hundreds of cities are pledging to rein in emissions, slash energy usage, and turn to renewable energy sources.

Mayors say they see greater urgency than national leaders do.

‘When there is a flood, a drought, torrential rains, those who show their face before the citizens and must offer a response are the mayors. So they are the ones who are most worried by the risks,’ said Marta Delgado, the environmental secretary for Mexico City.

‘We’re leading the way,’ Los Angeles Mayor Antonio Villaraigosa […]