The carbon detectives

Abstract

Even if countries agree to reduce greenhouse gas emissions, researchers face the monumental task of precisely monitoring the amounts of gases that are being emitted, and where. New tech will help, but the complications are many. To escape the worst ravages of climate change, humans have a steep path to climb. The Paris climate accord negotiated in 2015 aims to limit global warming to below 2 °C, and ideally no more than 1.5 °C, requiring rapid and deep cuts in greenhouse gas emissions. Even assuming the big emitters make the necessary commitments, researchers and policymakers will need to monitor emissions closely to catch any stumble. If countries stray too far from their targets, there may not be time to make up ground before the Earth hits catastrophic climate tipping points. As shown in this artist’s conception, NASA’s GeoCarb mission, planned for a 2021 launch, will map concentrations of carbon gases from a high, geostationary orbit, allowing it to scan across an area the size of the continental United States every 2 hours or so. Image courtesy of NASA/Lockheed Martin/University of Oklahoma. At the moment, national emissions are calculated by accountants, based on the activity in different economic sectors. Coal-fired power stations emit close to 1 kilogram of CO2 per kilowatt hour of electricity generated, so multiply that emission factor by the total energy generation and you get overall emissions. Doing the same for manufacturers, farms, and other emission sources gives the national total. In developed nations, this bottom-up accounting process estimates CO2 totals with claimed uncertainties of about 5%, says Riley Duren at the Jet Propulsion Laboratory (JPL) in Pasadena, CA, who leads the Megacities Carbon Project. This doesn’t sound so bad. But the approach has several drawbacks. “Methodologies are tricky to agree on,” says Annalisa Savaresi, specialist …