Dr. Gurney said that the errors seemed to be simple miscalculations. “I don’t think there’s any attempt to systematically or intentionally underestimate emissions,” he said. Although some cities correctly estimated their emissions, he noted, though “whether that’s right for the right reasons or right for the wrong reasons, it’s difficult to know.”
Dr. Gurney’s work receives funding from the National Institute of Standards and Technology, and one of the authors, Kimberly Mueller, is a scientist there. James R. Whetstone, an official in the institute’s greenhouse gas measurement program, called the new paper “an important step forward” in properly measuring greenhouse gases from cities. “What will serve the nation best is if we have a consistent way to state emissions that goes from the city level to the national level,” he said.
The National Institute of Standards and Technology, he noted, focuses much of its efforts on atmospheric monitoring, and so Dr. Gurney’s method can help “to measure the same thing in different ways,” and thus gain confidence in the results.
Earlier studies by researchers at the University of Michigan, Harvard and the federal government found that emissions of methane, another powerful greenhouse gas, were also undercounted by many cities. Dr. Gurney said that “both gasses should really be part of this systematic approach.”
The cities’ efforts so far, Dr. Gurney said, have been a laudable endeavor, but “they haven’t had a lot of tools to do it.” What’s more, he said, “Cities are struggling to pick up the garbage and fill potholes, much less keep detailed reports about their emissions.”
Reducing emissions in a city, he said, requires a deep understanding of where the biggest problems are, including specific traffic-choked highways and industries, so that the authorities can take focused actions that provide the greatest benefit at the lowest cost. Putting in high-occupancy vehicle lanes or rapid bus lanes on every highway could be wasteful; it would be better, he said, to know which road projects could do the most good.