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Plug-in hybrid cars release almost 5x more global warming emissions than lab-reported data show, according to a new analysis.

Growing Gap In Lab and Real-World CO2 Output

Statistics shows that PHEVs emit just one-fifth less CO₂ than traditional gas and diesel cars, based on analysis carried out by a non-profit organization. This differs sharply with laboratory estimates, which suggested a three-quarters reduction in emissions.

Analysts studied data from onboard energy use monitors of 800,000 cars sold in the EU between 2021 and 2023. The team discovered that real-world CO₂ output from PHEVs in 2023 were nearly five times higher than lab figures, increased from 3.5 times in 2021.

“Real-world emissions are increasing, while lab-reported figures are falling,” stated a lead researcher participating in the report. “This gap is growing and creates a serious problem. Consequently, PHEVs emit nearly as heavily as petrol vehicles.”

Primary Factors Behind the Discrepancy

Analysts linked the majority of the difference to inflated estimates of the “electric driving share” – the percentage of kilometers driven in electric power compared to total mileage. The team determined that only a quarter of travel was done in EV mode, while lab assumptions assumed over four-fifths.

Even, when operating in EV mode, pollution levels were well above lab projections. This happened because EV motors were not strong enough to function independently, leading to combustion motors burning fossil fuels for almost one-third of the distance completed in electric mode.

Regulatory and Financial Consequences

Based on calculations, the underestimation of PHEV CO2 output enabled several large carmaker groups to escape over €5bn in penalties from 2021 and 2023, by falsely simplifying compliance with European Union average fleet CO₂ standards.

Additionally, drivers of PHEVs would pay about €500 extra per year in running expenses than would be assumed under laboratory tests.

“The strong claims that automakers like to make about their PHEV vehicles are clearly far from the mark,” stated a transport expert. “Buyers are being duped into believing that by buying a PHEV, they are benefiting the planet and cutting costs. Actually, PHEVs are only slightly better than regular gas and diesel cars in terms of fuel use, CO₂ production, and running expenses.”

Policy Discussion and Automotive Pressure

Plug-in hybrid cars have recently been drawn back into political debates as carmakers have pressed the EU to relax CO₂ targets. A planned ban on new internal combustion vehicles in 2035 has faced heavy pressure from the automotive industry and opposition from member states with large automotive manufacturing.

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

One external energy policy expert, who was unaffiliated with the research, described the report a “very useful contribution” after a long period in which segments of the car sector argued there was insufficient information to accurately assess real-world emissions.

“The results demonstrate, beyond any doubt, that the gap in official and real-world PHEV fuel consumption and CO₂ output is much, much greater than for petrol or conventional vehicles,” the expert stated. “Any regulatory adjustments concerning PHEVs should be made with extreme caution and in the light of that evidence.”