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Plug-in hybrid cars emit nearly 5x greater global warming emissions than official data indicate, according to a recent report.

Growing Gap Between Official and Actual CO2 Output

Data shows that PHEVs emit just 19% lower CO₂ than conventional gas and diesel cars, based on analysis conducted by a advocacy organization. That differs significantly with lab tests, which suggested a three-quarters decrease in emissions.

Analysts studied data from in-vehicle energy use meters of eight hundred thousand vehicles sold in the EU from 2021 and 2023. The team discovered that real-world CO₂ emissions from PHEVs in 2023 were nearly five times greater than lab estimates, up from 3.5 times in 2021.

“Real-world emissions are rising, while official figures are falling,” said a senior researcher participating in the report. “That discrepancy is growing and poses a serious issue. As a result, PHEVs pollute almost as much as gasoline vehicles.”

Primary Reasons Driving the Emissions Gap

Analysts linked the majority of the difference to overestimates of the “utility factor” – the ratio of miles driven in electric mode relative to overall mileage. The team determined that just 27% of travel was done in electric mode, while official estimates suggested over four-fifths.

Additionally, when running in electric mode, pollution levels were significantly higher than official estimates. That happened because electric motors were insufficiently powerful sufficient to operate independently, leading to combustion motors using fossil fuels for almost a third of the distance completed in EV mode.

Policy and Financial Consequences

According to estimates, the lowballing of PHEV CO2 output enabled four major carmaker groups to avoid more than €5bn in fines from 2021 and 2023, by falsely simplifying compliance with EU fleet-average CO₂ standards.

Additionally, drivers of PHEVs could spend about €500 extra per year in running costs than would be estimated under laboratory tests.

“The bold statements that manufacturers often promote about their plug-in hybrid vehicles are clearly far from the truth,” stated a transport expert. “Buyers are being misled into thinking that by purchasing a PHEV, they are benefiting the planet and cutting money. In reality, PHEVs are only slightly better than regular gas and diesel cars in terms of energy consumption, CO₂ production, and running costs.”

Policy Debate and Industry Lobbying

Hybrid vehicles have lately been drawn again into political discussions as automakers have pressed the EU to weaken CO₂ standards. A proposed prohibition on new combustion engine vehicles in 2035 has faced heavy pressure from the car sector and resistance from EU countries with large car manufacturing.

Several high-level politicians have suggested plug-in hybrids as a potential “compromise” solution to introduce in the legislation.

An external energy economics expert, who was unaffiliated with the research, called the report a “highly valuable contribution” after years in which parts of the automotive industry claimed there was too little information to accurately evaluate real-world CO2 output.

“These findings show, without question, that the difference in official and real-world PHEV energy use and CO₂ output is significantly greater than for petrol or conventional vehicles,” they said. “All regulatory adjustments regarding PHEVs should be made with utmost care and in the light of that evidence.”