Scientists track carbon footprints of large cities responsible for human-caused global warming

LOS ANGELES - Scientists across the nation are working to track the carbon footprints of large cities that increasingly contribute to a large part of human-caused global warming.

Instruments perched in the mountains above Los Angeles monitor carbon dioxide, methane and other greenhouse gases spewing from factories and freeways. Similar contraptions atop the Eiffel Tower and elsewhere around Paris keep a pulse on emissions from smokestacks and automobile tailpipes. There's also talk of outfitting Sao Paulo, Brazil, with sensors that sniff the byproducts of burning fossil fuels.

For years, greenhouse pollutants have been closely monitored around the planet by stations on the ground and in space.

Now, scientists are eyeing megacities, aiming to observe emissions in the atmosphere as a first step toward independently verifying whether local -- and often lofty -- climate goals are being met.