Cities in the United States are woefully underestimating their carbon emissions and that could be hampering their ability to fight climate change, according to a new study published this week in the journal Nature Communications. Reuters reports that the 48 cities in the study underreported their emissions by an average of 18 percent between 2010 and 2015.
Extrapolating that level of underestimation to all American cities produces an annual total of unreported emissions equaling 129 million metric tons. That’s 25 percent higher than the emissions from the entire state of California in 2015, reports John Schwartz for the New York Times.
Per the Times, three quarters of all carbon dioxide released by burning fossil fuels emanates from cities, and their growth shows no signs of slowing down.
The researchers behind the study compared the self-reported emissions from the 48 cities to estimates generated using a new data tool that compiles publicly available data on known sources of emissions, including factories, power plants, traffic data and population using census tracts. The tool, called Vulcan, also checks its work against measurements of concentrations of carbon dioxide in the atmosphere.
Some cities’ reported emissions were outstripped by Vulcan’s estimates to the tune of 145 percent.
The paper’s authors make clear they’re not suggesting cities are knowingly underreporting their emissions. “They’re very well intentioned,” Kevin Gurney, a climate researcher at Northern Arizona University and lead author of the study, tells Donna Lu of New Scientist. “In some ways,” Gurney tells Matt Simon of Wired, “they're being burdened with doing a job they shouldn't have to do.”
Part of the problem is that all these cities are coming up with their own ways of trying to account for their emissions because there’s no national template or standard methodology for doing so. If a city has trouble getting the numbers to quantify, say, emissions from cement production in their region they might just leave it out of the final tally, according to Wired. Of course the opposite can also occur, with a city overreporting emissions.
Gurney gives Flagstaff, Arizona, where he’s based, as an example. The city uses gasoline sales as a proxy for automobile emissions. It sounds reasonable, except that Flagstaff sits at the intersection of several major freeways. “The problem is that Flagstaff is a really large fueling stopover,” Gurney tells New Scientist. Cars that may just be passing through Flagstaff end up contributing a whole gas tank’s worth of emissions to the city’s tally.
“We haven’t had a systematic regulatory approach to controlling greenhouse gas emissions in the U.S.,” Gurney tells the Times. “A crucial step toward any sort of policy has to be, ‘What are our emissions, where are they, how much are they and what’s making them happen?’”
Accurately assessing emissions at the local level is a crucial step towards achieving the ambitious goals of the Biden administration to reduce the U.S. contribution to climate change. And major cities have made aggressive pledges to shrink their carbon footprints. New York City committed to slashing emissions by 80 percent by 2050 while Washington (D.C.), San Francisco and Seattle have pledged to go carbon neutral by mid-century, per Reuters.
Patrick Drupp, the associate director of legislative and administrative advocacy at the Sierra Club, tells the Times “as we work to tackle the climate crisis and protect all communities from harm, it’s clear that accurate data is essential to making effective decisions.”