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Plug-in hybrid electric vehicles release nearly 5x more global warming pollution than official data show, according to a recent report.

Widening Gap Between Official and Actual Emissions

Data reveals that PHEVs release only 19% less CO₂ than traditional petrol and diesel cars, according to research conducted by a non-profit organization. That contrasts significantly with laboratory tests, which assumed a 75% decrease in emissions.

Analysts studied information from in-vehicle fuel consumption monitors of eight hundred thousand cars registered in Europe between 2021 and 2023. They found that actual CO₂ output from PHEVs in 2023 were 4.9 times greater than official figures, increased from 3.5 times in 2021.

“Actual emissions are rising, while official figures are falling,” said a senior researcher involved in the study. “That gap is growing and creates a significant issue. Consequently, PHEVs emit nearly as heavily as gasoline vehicles.”

Primary Factors Behind the Discrepancy

Analysts linked most of the gap to overestimates of the “utility factor” – the ratio of miles travelled in battery mode compared to overall mileage. The team found that just 27% of driving was completed in electric mode, while official estimates assumed 84%.

Even, when running in EV mode, emission levels were significantly higher than official estimates. This happened because EV motors were not strong enough to function alone, resulting to combustion motors burning gasoline for almost one-third of the distance completed in EV mode.

Regulatory and Economic Implications

Based on estimates, the underestimation of PHEV CO2 output allowed four large automaker groups to avoid more than €5bn in fines between 2021 and 2023, by falsely easing compliance with EU fleet-average CO₂ targets.

Furthermore, owners of PHEVs could spend about €500 more per year in running costs than is assumed under lab conditions.

“The bold claims that automakers like to make about their plug-in hybrid cars are clearly far from the mark,” stated a transport analyst. “Consumers are being misled into thinking that by buying a PHEV, they are helping the planet and saving costs. In reality, PHEVs are only slightly improved than regular petrol and diesel vehicles in terms of fuel consumption, CO₂ emissions, and operating costs.”

Political Discussion and Automotive Lobbying

Plug-in hybrid vehicles have recently been drawn back into policy debates as carmakers have lobbied the EU to relax CO₂ standards. A planned prohibition on sales of new internal combustion cars in 2035 has faced intense pressure from the automotive industry and opposition from EU countries with significant automotive manufacturing.

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

An independent energy economics specialist, who was unaffiliated with the research, called the analysis a “highly valuable contribution” after a long period in which parts of the automotive industry claimed there was insufficient information to accurately evaluate actual emissions.

“The results demonstrate, beyond any doubt, that the gap in lab and actual PHEV energy use and CO₂ emissions is much, much greater than for gasoline or conventional vehicles,” they said. “All regulatory changes regarding PHEVs should be made with utmost caution and considering this evidence.”