AP EXPLAINS: How Madrid talks fell short on climate ambition

This year's U.N. climate negotiations in Madrid, the longest in 25 nearly annual such gatherings, ended Sunday with major polluters resisting calls to ramp up efforts to keep global warming at bay.Faced with the tough task of reconciling the demands of scientists, protesters on the streets and governments back home, the negotiators ended up disappointing many and leaving for next year's talks in Glasgow, Scotland, key issues such as the regulation of global carbon markets.While it wasn't officia