Every time Los Angeles exhales, odd-looking gadgets anchored in the mountains above the city trace the invisible puffs of carbon dioxide, methane and other greenhouse gases that waft skyward.
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.
Now, some scientists are eyeing large cities – with LA and Paris as guinea pigs – and aiming to observe emissions in the atmosphere as a first step toward independently verifying whether local – and often lofty – climate goals are being met.
For the past year, a high-tech sensor poking out from a converted shipping container has stared at the Los Angeles basin from its mile-high perch on Mount Wilson, a peak in the San Gabriel Mountains that’s home to a famous observatory and communication towers.
Like a satellite gazing down on Earth, it scans more than two dozen points from the inland desert to the coast. Every few minutes, it rumbles to life as it automatically sweeps the horizon, measuring sunlight bouncing off the surface for the unique fingerprint of carbon dioxide and other heat-trapping gases.
In a storage room next door, commercially available instruments that typically monitor air quality double as climate sniffers. And in nearby Pasadena, a refurbished vintage solar telescope on the roof of a laboratory on the California Institute of Technology campus captures sunlight and sends it down a shaft 60 feet below where a prism-like instrument separates out carbon dioxide molecules.
On a recent April afternoon atop Mount Wilson, a brown haze hung over the city, the accumulation of dust and smoke particles in the atmosphere.
This summer, technicians will install commercial gas analyzers at a dozen more rooftops around the greater LA region.