A new study from researchers at Northern Arizona University has raised concerns about the accuracy of a widely used global greenhouse gas emissions database backed by the Climate TRACE consortium, a climate-monitoring group co-founded by former U.S. Vice President Al Gore.
The research, published in the journal Environmental Research Letters, found that the Climate TRACE database may significantly underestimate carbon dioxide (CO2) emissions from cars and trucks in cities across the United States.
According to the study, vehicle emissions in the database were, on average, about 70% lower than estimates from another well-established emissions system called Vulcan.
The study was led by Kevin Gurney, a professor at Northern Arizona University’s School of Informatics, Computing, and Cyber Systems.
Gurney and his team compared Climate TRACE data with the Vulcan emissions database, which has been developed over the past two decades using official traffic information, fuel consumption records, and atmospheric measurements.
The researchers examined emissions from 260 U.S. cities. In some cities, including Indianapolis and Nashville, the Climate TRACE estimates were more than 90% lower than the Vulcan estimates.
The Climate TRACE project uses artificial intelligence and satellite data to estimate greenhouse gas emissions around the world.
The system has attracted attention because it promises faster and more detailed emissions tracking than traditional methods. Supporters believe these tools could help governments and organizations better understand where pollution is coming from and how to reduce it.
However, the Northern Arizona University team says the new findings highlight the need for careful scientific review and transparency when using AI-based systems for climate monitoring.
Gurney said accurate emissions data is essential for making effective climate policies. If emissions are underestimated, governments and policymakers may not fully understand the scale of pollution problems or where action is most needed.
The researchers stressed that no emissions system is perfect. Even the Vulcan database has an estimated uncertainty of around 14%.
But they argued that the much larger differences found in the Climate TRACE data are concerning because transportation is one of the biggest sources of greenhouse gas emissions in cities.
The study also follows earlier research by Gurney’s group that found similar discrepancies in Climate TRACE estimates for power plant emissions. Together, the studies suggest the database may underestimate a large portion of fossil fuel emissions in urban areas.
Climate TRACE responded after the study was published, saying the researchers may have analyzed an outdated version of its transportation dataset.
According to the consortium, a temporary software bug affected some road transportation estimates in 2025, but the issue was identified and corrected later that year.
The group said that with the updated data, its emissions estimates differ from the Vulcan database by only about 6% on average at the city level and around 1.4% at the county level. Climate TRACE argues these differences are normal for independent emissions inventories.
The debate highlights a growing challenge in climate science: balancing new AI-driven technologies with the need for rigorous scientific validation and public trust.
