American Cities Are Way Underreporting Their Carbon Footprints


Having each city build an individual SRI is like developing a national weather forecasting system by asking each county to characterize their local weather, then gathering up all those systems into one cohesive model. “Well, that wouldn’t make any sense when you’re doing weather forecasting,” says Gurney. “In the same way, a greenhouse gas emissions system shouldn’t be every single entity doing this redundantly themselves.”

Instead, Gurney argues that the Vulcan system can shoulder the burden of calculating carbon levels for cities across the US. He and his colleagues have been developing the system for 15 years, incorporating two dozen data sets to thoroughly quantify sources of emissions across the country in fine detail. Vulcan looks at traffic, census, and air quality data, and takes an inventory of the emissions from all the power plants in the US. In some cities, like Los Angeles, the model is so detailed that it can discern how emissions vary block by block. The team has been able to confirm Vulcan’s modeling of emissions with atmospheric measures of CO2 across the US.

And in their new research, they found that city self-reports are often out of step when compared to Vulcan’s outputs. Their study found that some places, like Flagstaff and Palo Alto, significantly overreported their emissions (by about 60 percent and 40 percent, respectively). Others, like the California city of Torrance, underreported by over 100 percent, according to the study. (The team adjusted Vulcan’s output for each city, by the way. If one left out industrial fuel use, for instance, so would Vulcan, in order to better square the results. This means that Vulcan would also come up with somewhat of an underestimation, compared to a complete report.)

So why is it important to resolve these discrepancies? For one thing, city agencies can end up sinking considerable time and resources into mitigating emissions—like by creating more public transport and green spaces, or making the built environment friendlier for pedestrians—so they should have access to the most accurate data possible to figure out what to fund. And local data constantly changes as a city naturally transforms over time, so policymakers can find themselves tasked with making decisions based on a recent SRI report that’s already out of date.

Vulcan, by contrast, is consistently updated every two or three years with new data across the board, which can characterize a city’s growth over time. “We’re suggesting that this needs to be done in an ongoing fashion,” says Gurney. (He says governments can reach out to his team to start digging into Vulcan’s data on their cities.)

Might Vulcan, then, become a sort of standardized platform for American cities to more accurately measure their emissions? “I think that’s plausible, for sure,” says Louisiana State University environmental scientist Brian Snyder, who wasn’t involved in the work. “And I think it’d be a vast improvement upon what they’re doing right now.”

What cities are best equipped to transform at the moment, Snyder argues, is transportation. “If you want to reduce your emissions from transport, you have to know what your emissions are to begin with,” Snyder says. “And one of the nice things that Vulcan does is it sort of shows you—very specifically to the grid space—where they at least think those emissions are coming from.” This could help city agencies figure out where to bolster public transportation, for instance.

But there’s only so much a city can do to reduce emissions in the short term, Snyder adds. “A lot of stuff has been baked into the cake for 100 years.” Oil refineries remain a scar on the landscape for many cities, for instance.

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