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Plug-in hybrid electric vehicles produce nearly five times more planet-heating emissions than official data indicate, according to a new analysis.

Widening Gap Between Official and Real-World Emissions

Data shows that PHEVs emit only 19% less CO₂ than conventional gas and diesel cars, based on research carried out by a advocacy organization. That differs sharply with lab tests, which suggested a 75% decrease in emissions.

Researchers studied information from onboard energy use meters of eight hundred thousand cars registered in the EU from 2021 and 2023. They found that actual CO₂ output from PHEVs in 2023 were nearly five times higher than official estimates, increased from 3.5 times in 2021.

“Actual emissions are increasing, while official emissions are decreasing,” said a senior analyst involved in the report. “This gap is widening and creates a significant issue. Consequently, PHEVs pollute almost as much as petrol cars.”

Primary Factors Behind the Emissions Gap

Researchers linked most of the gap to inflated estimates of the “electric driving share” – the percentage of miles driven in battery mode compared to total distance. The team found that only a quarter of driving was completed in EV mode, whereas lab estimates suggested 84%.

Even, when running in electric mode, pollution levels were well above lab projections. This happened because EV motors were insufficiently powerful sufficient to operate alone, leading to combustion motors burning fossil fuels for almost a third of the distance covered in electric mode.

Regulatory and Economic Consequences

Based on calculations, the lowballing of PHEV emissions enabled several large carmaker groups to avoid more than €5bn in penalties from 2021 and 2023, by artificially simplifying compliance with European Union fleet-average CO₂ targets.

Additionally, owners of PHEVs could pay about €500 more per year in operating costs than is estimated under laboratory tests.

“The bold statements that manufacturers like to make about their plug-in hybrid cars are clearly way off the truth,” stated a transport expert. “Consumers are being duped into believing that by buying a PHEV, they are helping the environment and saving costs. Actually, PHEVs are only slightly improved than regular petrol and diesel cars in terms of energy consumption, CO₂ emissions, and running expenses.”

Political Debate and Industry Lobbying

Plug-in hybrid cars have lately been drawn back into policy discussions as automakers have pressed the European Union to weaken CO₂ standards. A planned ban on sales of new internal combustion cars in 2035 has faced heavy pressure from the car industry and opposition from member states with significant automotive manufacturing.

Several high-level politicians have suggested PHEVs as a potential “compromise” option to introduce in the legislation.

One external energy economics expert, who was not involved with the research, described the analysis a “highly valuable contribution” after a long period in which segments of the car industry claimed there was too little data to properly evaluate actual emissions.

“The results show, without question, that the gap between official and real-world PHEV fuel consumption and CO₂ output is significantly larger than for petrol or diesel cars,” the expert said. “Any policy adjustments regarding PHEVs should be implemented with extreme care and in the light of that data.”