Climate TRACE Emissions Database Undercounts Vehicle CO2 by 70%, Study Warns

Major Errors Discovered in Al Gore's Climate TRACE Emissions Database

A groundbreaking study from Northern Arizona University (NAU) is casting serious doubt on the accuracy of one of the world's most prominent greenhouse gas tracking tools. Researchers have concluded that the Climate TRACE database — developed by a consortium co-founded by former Vice President Al Gore — is significantly underreporting carbon dioxide emissions produced by vehicles in American cities, sometimes missing the mark by more than 90%.

The findings, published in the peer-reviewed journal Environmental Research Letters, reveal that across 260 U.S. cities, the Climate TRACE database underestimates vehicle-related CO2 emissions by an average of 70%. The implications for climate policy and emissions reduction strategies could be substantial.

What the Research Found

The study was led by Kevin Gurney, a professor in NAU's School of Informatics, Computing, and Cyber Systems (SICCS). His team specifically examined how Climate TRACE reports carbon dioxide output from cars and trucks in urban environments — a critical category of fossil fuel emissions that plays an outsized role in city-level climate planning.

To benchmark the Climate TRACE figures, researchers cross-referenced them with data from Vulcan, an independent onroad emissions database developed by Gurney's own laboratory. The Vulcan system draws on verified traffic records and official energy consumption data to generate reliable emissions estimates, carrying an uncertainty margin of roughly 14%.

The contrast between the two datasets was stark.

"The Climate TRACE CO2 emissions were, on average, 70% lower than those same emissions in the Vulcan onroad CO2 emissions database," said Bilal Aslam, a SICCS postdoctoral researcher and co-investigator on the study.

Some Cities Showed Gaps Exceeding 90%

The discrepancies weren't uniform. Certain cities revealed dramatically larger gaps between the two data sources. According to Pawlok Dass, a research associate at SICCS, cities like Indianapolis and Nashville showed Climate TRACE figures that fell more than 90% below what Vulcan recorded — a difference so large it raises fundamental questions about the database's methodology.

The research team also believes these inaccuracies are unlikely to be limited to the United States. They suspect similar underestimates may exist in Climate TRACE data for cities around the world, potentially undermining global climate accountability efforts.

A Pattern of Concern

This is not the first time Climate TRACE's accuracy has been questioned by NAU researchers. An earlier study from the same team identified comparable problems in how Climate TRACE estimates emissions from power plants, another major source of fossil fuel-based CO2.

Taken together, Gurney says the two studies suggest that Climate TRACE may be significantly underreporting more than half of U.S. fossil fuel CO2 emissions in urban settings — a troubling pattern for a tool used to inform climate decisions at the highest levels.

"Given the importance of vehicle CO2 emissions in cities, we carefully examined the Climate TRACE data which relied on promising new artificial intelligence-based approaches," Gurney explained. "Our results suggest that the Climate TRACE data significantly underestimate over half of U.S. fossil fuel-based CO2 emissions in cities."

AI Promise vs. Scientific Rigor

Climate TRACE employs artificial intelligence to monitor and estimate greenhouse gas emissions globally — an innovative approach that researchers acknowledge holds genuine promise for environmental tracking. However, the NAU team argues that technological ambition must be paired with rigorous scientific standards.

In their view, transparency, independent expert review, and methodological integrity are non-negotiable when producing data that feeds directly into climate legislation and public policy. Without these safeguards, even well-intentioned tools can mislead the decision-makers who rely on them.

The published study includes a set of concrete recommendations designed to help Climate TRACE improve its accuracy, providing a constructive path forward for the consortium's ongoing work.

"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 stated. "Without this, we mislead decision makers and potentially lose public trust in our ability to tackle climate change."

About the Lead Researcher

Kevin Gurney brings more than two decades of expertise to this field, working at the intersection of atmospheric science, ecology, and public policy. His federally supported Vulcan and Hestia projects map greenhouse gas emissions at extraordinary resolution — from individual roadways and power plants down to neighborhood-level detail — helping identify emissions hotspots across the country.

With over 180 published scientific papers and more than 20,000 citations to his name, Gurney is a recognized authority in the field. He has participated in United Nations climate negotiations for over 25 years and serves as a lead author for the Intergovernmental Panel on Climate Change (IPCC). His work also contributed to a recent U.S. National Academy report titled Greenhouse Gas Emissions for Decisionmaking.