A new study is raising concerns about one of the world's most prominent efforts to track air pollution. Researchers at Northern Arizona University say the Climate TRACE database may be undercounting urban vehicle carbon dioxide pollution by 70%.
The findings, published in Environmental Research Letters, focus on cars and trucks in 260 United States cities. According to NAU professor Kevin Gurney and colleagues, as detailed by the NAU Review, the issue matters far beyond a single dataset: if air pollution is measured incorrectly, climate policy, public spending, and public confidence can all take a hit.
Gurney, of NAU's School of Informatics, Computing, and Cyber Systems, analyzed urban vehicle carbon dioxide pollution reported by Climate TRACE, a consortium co-founded by former Vice President Al Gore. The team compared those figures with the Vulcan database, produced by Gurney's laboratory and calibrated against official traffic and energy consumption data, according to the NAU Review.
That side-by-side comparison found a major gap. The researchers said Climate TRACE's vehicle pollution estimates were, on average, far lower than those shown in Vulcan, which Gurney's lab has spent years developing to map air pollution output across the U.S. at high resolution.
Bilal Aslam, a postdoc at SICCS and co-investigator on the study, said Vulcan is not flawless and carries an uncertainty of about 14%, per the NAU Review. However, that margin is still much smaller than the discrepancy the team found when comparing city-level pollution data.
According to the study, some cities showed especially steep differences. Research associate Pawlok Dass said places including Indianapolis and Nashville came in more than 90% lower in the Climate TRACE database than in Vulcan's on-road records, per the NAU Review. The authors also said they suspect similar underestimation may be happening globally.
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Air pollution databases are increasingly shaping where cities focus climate action, how governments allocate money, and which sectors are targeted first for cuts. If transportation pollution in a city looks much smaller than it really is, leaders could end up underinvesting in cleaner transit, road planning, electrification, or other measures that would make the biggest difference.
"Accurate estimation of greenhouse gas (GHG) emissions at the infrastructure scale remains essential to climate science and policy applications. Vehicle emissions often dominate GHG emissions in urban areas and are rapidly increasing globally," the researchers wrote in the study.
This is especially critical as air pollution worsens and more people live in areas with levels already too high. It's even more so when fully considering the health concerns this brings.
The researchers noted that artificial intelligence can still be a powerful tool for environmental monitoring but said it needs scientific transparency, rigorous validation, and expert review to guide real-world climate decisions.
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"We will never estimate emissions with perfect accuracy, but we must ensure that the data shared with policymakers and the public is unbiased and meets best practices and the most rigorous scientific standards available," Gurney said, according to the NAU Review. "Without this, we mislead decision makers and potentially lose public trust in our ability to tackle climate change."
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