Halfway around the globe, similar contraptions atop the Eiffel Tower and elsewhere around Paris keep a pulse on emissions from smokestacks and automobile tailpipes. And there is talk of outfitting Sao Paulo, Brazil, with sensors that sniff the byproducts of burning fossil fuels.
It’s part of a budding effort to track the carbon footprints of megacities, urban hubs with over 10 million people that are increasingly responsible for human-caused global warming.
For years, carbon dioxide and other greenhouse pollutants have been closely monitored around the planet by stations on the ground and in space. Last week, worldwide levels of carbon dioxide reached 400 parts per million at a Hawaii station that sets the global benchmark , a concentration not seen in millions of years.