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Plug-in hybrid cars produce almost five times greater global warming emissions than lab-reported figures indicate, as per a new analysis.

Growing Gap In Official and Actual Emissions

Data shows that PHEVs emit only 19% less CO₂ than traditional petrol and diesel cars, according to research carried out by a advocacy group. That differs significantly with laboratory tests, which suggested a three-quarters reduction in pollution.

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

“Real-world emissions are increasing, while official emissions are decreasing,” said a senior researcher involved in the report. “That discrepancy is growing and poses a serious issue. Consequently, PHEVs pollute almost as heavily as petrol cars.”

Key Reasons Driving the Discrepancy

Analysts attributed the majority of the difference to inflated estimates of the “utility factor” – the percentage of miles driven in electric mode compared to total distance. They determined that just a quarter of driving was completed in electric mode, whereas official assumptions assumed over four-fifths.

Additionally, when running in EV mode, emission amounts were well above lab projections. This occurred because EV motors were not strong sufficient to function independently, resulting to engines using gasoline for almost one-third of the travel completed in EV mode.

Regulatory and Economic Consequences

Based on estimates, the lowballing of PHEV CO2 output allowed several large carmaker companies to escape over €5bn in penalties between 2021 and 2023, by falsely easing adherence with EU fleet-average CO₂ standards.

Additionally, owners of PHEVs could pay approximately €500 extra annually in running expenses than is estimated under laboratory tests.

“The strong claims that automakers often promote about their plug-in hybrid vehicles are clearly way off the mark,” stated a transport expert. “Buyers are being misled into believing that by buying a PHEV, they are helping the planet and saving costs. In reality, PHEVs are only slightly better than regular petrol and diesel vehicles in terms of energy consumption, CO₂ production, and running costs.”

Policy Discussion and Automotive Pressure

Plug-in hybrid cars have recently been brought again into political discussions as automakers have lobbied the European Union to weaken CO₂ targets. A planned prohibition on new internal combustion vehicles in 2035 has faced intense lobbying from the automotive industry and resistance from EU countries with large car manufacturing.

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

One external energy policy specialist, who was unaffiliated with the study, called the analysis a “very useful addition” after a long period in which segments of the car sector claimed there was too little information to properly assess actual CO2 output.

“The results demonstrate, without question, that the difference between lab and real-world PHEV fuel consumption and CO₂ output is significantly larger than for gasoline or diesel vehicles,” they stated. “Any policy adjustments concerning PHEVs should be made with utmost care and considering that data.”