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Plug-in hybrid cars produce almost 5x greater global warming pollution than official data indicate, according to a recent report.

Widening Discrepancy In Lab and Actual Emissions

Data shows that PHEVs release just one-fifth less CO₂ than traditional gas and diesel cars, based on research conducted by a non-profit group. That differs sharply with laboratory tests, which suggested a three-quarters reduction in emissions.

Analysts examined information from in-vehicle fuel consumption monitors of 800,000 cars registered in the EU from 2021 and 2023. They discovered that actual CO₂ output from PHEVs in 2023 were nearly five times greater than lab estimates, increased from 3.5 times in 2021.

“Actual CO2 output are increasing, while official emissions are decreasing,” stated a senior researcher participating in the report. “This discrepancy is growing and poses a serious issue. As a result, PHEVs emit almost as much as petrol cars.”

Key Factors Behind the Emissions Gap

Researchers attributed most of the difference to overestimates of the “utility factor” – the ratio of miles driven in battery mode relative to total mileage. The team determined that only 27% of driving was completed in electric mode, whereas official assumptions suggested over four-fifths.

Additionally, when running in EV mode, pollution levels were well above official projections. This occurred because EV motors were not strong sufficient to function independently, resulting to engines using gasoline for almost a third of the distance covered in EV mode.

Regulatory and Financial Implications

Based on estimates, the lowballing of PHEV CO2 output allowed several major automaker companies to avoid more than €5bn in fines from 2021 and 2023, by artificially easing adherence with European Union fleet-average CO₂ targets.

Additionally, owners of PHEVs would spend about €500 extra annually in running expenses than would be assumed under laboratory conditions.

“The bold statements that manufacturers often promote about their PHEV vehicles are obviously way off the mark,” stated a transport expert. “Consumers are being misled into thinking that by purchasing a PHEV, they are helping the planet and saving money. In reality, PHEVs are little better than standard petrol and diesel cars in terms of fuel consumption, CO₂ emissions, and running costs.”

Policy Debate and Industry Pressure

Hybrid vehicles have recently been drawn again into political debates as carmakers have pressed the EU to weaken CO₂ standards. A proposed ban on new internal combustion vehicles in 2035 has faced intense lobbying from the car sector and resistance from member states with significant automotive manufacturing.

Several senior officials have suggested plug-in hybrids as a possible “flexibility” option to include in the legislation.

One independent energy policy expert, who was not involved with the study, called the report a “very useful contribution” after years in which parts of the automotive industry argued there was insufficient information to accurately assess real-world CO2 output.

“These findings demonstrate, beyond any doubt, that the gap between official and actual PHEV fuel consumption and CO₂ emissions is much, much greater than for gasoline or diesel cars,” they stated. “All policy adjustments concerning PHEVs should be made with extreme caution and in the light of this data.”