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CLIMATE CHANGE
Scientists monitor greenhouse gases in urban areas as a first step to gauging success of climate initiatives worldwide.
At the top of Mount Wilson in southern California, an infrared sensor scans the horizon, silently mapping carbon dioxide levels across Los Angeles. In the city below, scientists fire lasers into the sky to measure the daily rise and fall of a dome of pollution that caps the valley. Other instruments perched on towers are set to track air as it flows into the city and out again, laden with emissions. Eventually, instrumented aircraftwill join the effort. Once the operation is fully under way in 2013, the CO2 that Los Angeles exhales will be monitored and quantified to a degree well beyond that of any other major city.
United Nations data suggest that cities are responsible for some 70% of global greenhouse-gas emissions and that countries with high urbanization rates emit more CO2 per capita (see 'Urban emitters'). By closely tracking emissions in Los Angeles and other megacities, researchers hope to test greenhouse-gas monitoring systems that may one day allow scientists to gauge the success of local - and, ultimately, national - climate initiatives. Early results presented this week at the American Geophysical Union meeting in San Francisco, California, offer promising signs that such independent verification is possible through a combination of atmospheric measurements and modelling.
"Megacity emissions are both important and scientifically tractable," says Riley Duren, a systems engineer who is spearheading the monitoring initiative at NASA's Jet Propulsion Laboratory (JPL) in Pasadena, California. Scientists might be a couple of decades away from being able to track all anthropogenic greenhouse-gas emissions at high resolution from...