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Plug-in hybrid cars release nearly 5x greater planet-heating pollution than official figures show, according to a recent analysis.

Widening Discrepancy In Lab and Actual Emissions

Data shows that PHEVs emit just 19% less CO₂ than traditional petrol and diesel cars, based on analysis carried out by a non-profit organization. This differs significantly with lab tests, which assumed a three-quarters decrease in emissions.

Analysts studied information from in-vehicle energy use monitors of 800,000 vehicles registered in Europe between 2021 and 2023. The team found that real-world CO₂ output from PHEVs in 2023 were nearly five times higher than official estimates, increased from 3.5 times in 2021.

“Real-world CO2 output are rising, while lab-reported emissions are falling,” said a lead researcher participating in the report. “That discrepancy is growing and poses a significant problem. As a result, PHEVs emit nearly as heavily as gasoline cars.”

Primary Factors Behind the Discrepancy

Analysts attributed most of the difference to overestimates of the “utility factor” – the ratio of miles travelled in battery power compared to total mileage. They determined that only a quarter of driving was completed in EV mode, while lab estimates suggested over four-fifths.

Even, when running in electric mode, emission amounts were significantly higher than official projections. That happened because EV motors were not strong enough to function independently, leading to combustion motors using fossil fuels for nearly a third of the distance completed in EV mode.

Policy and Economic Consequences

Based on calculations, the underestimation of PHEV CO2 output allowed several large automaker companies to escape more than €5bn in penalties from 2021 and 2023, by falsely simplifying adherence with EU average fleet CO₂ standards.

Furthermore, owners of PHEVs could pay approximately €500 extra annually in running costs than is estimated under laboratory conditions.

“The strong claims that automakers like to make about their plug-in hybrid cars are clearly far from the mark,” stated a automotive expert. “Buyers are being misled into believing that by purchasing a PHEV, they are helping the environment and cutting money. In reality, PHEVs are only slightly improved than regular petrol and diesel vehicles in terms of fuel consumption, CO₂ production, and running expenses.”

Political Discussion and Automotive Pressure

Plug-in hybrid cars have recently been brought back into political discussions as automakers have pressed the EU to relax CO₂ standards. A planned ban on new internal combustion cars in 2035 has faced intense pressure from the car industry and opposition from EU countries with large automotive industries.

Some high-level officials have proposed PHEVs as a potential “compromise” solution to include in the regulation.

An independent energy economics specialist, who was not involved with the research, described the analysis a “highly valuable addition” after years in which parts of the automotive sector argued there was too little data to accurately evaluate real-world emissions.

“These findings demonstrate, without question, that the difference in lab and actual PHEV energy use and CO₂ output is much, much larger than for gasoline or conventional vehicles,” they stated. “All policy changes regarding PHEVs should be made with utmost care and considering this evidence.”