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PHEVs emit nearly five times greater global warming pollution than lab-reported figures indicate, according to a new report.

Widening Discrepancy Between Lab and Real-World CO2 Output

Data shows that PHEVs release just one-fifth less CO₂ than conventional petrol and diesel vehicles, based on analysis conducted by a advocacy organization. That differs sharply with lab estimates, which suggested a three-quarters reduction in emissions.

Analysts examined data from onboard fuel consumption monitors of eight hundred thousand vehicles sold in the EU between 2021 and 2023. The team found that actual CO₂ output from PHEVs in 2023 were 4.9 times greater than official estimates, increased from three and a half times in 2021.

“Actual emissions are increasing, while lab-reported figures are falling,” stated a senior researcher participating in the study. “That discrepancy is growing and creates a significant problem. As a result, PHEVs emit almost as much as petrol cars.”

Primary Factors Behind the Emissions Gap

Analysts attributed most of the gap to overestimates of the “electric driving share” – the ratio of kilometers driven in electric mode relative to overall mileage. The team found that just 27% of travel was done in EV mode, while lab estimates suggested over four-fifths.

Additionally, when running in electric mode, emission levels were significantly higher than official estimates. That occurred because electric motors were not strong enough to operate independently, leading to engines using fossil fuels for nearly a third of the travel covered in EV mode.

Policy and Financial Consequences

According to calculations, the underestimation of PHEV emissions enabled four large automaker companies to escape more than €5bn in fines from 2021 and 2023, by artificially easing adherence with European Union average fleet CO₂ targets.

Furthermore, owners of PHEVs would pay about €500 more annually in operating expenses than is estimated under laboratory conditions.

“The strong claims that automakers often promote about their plug-in hybrid cars are clearly way off the mark,” commented a automotive analyst. “Consumers are being duped into thinking that by buying a PHEV, they are benefiting the planet and cutting costs. Actually, PHEVs are little better than standard petrol and diesel vehicles in terms of fuel use, CO₂ production, and running costs.”

Political Discussion and Automotive Lobbying

Plug-in hybrid vehicles have recently been drawn again into political discussions as automakers have lobbied the European Union to weaken CO₂ targets. A proposed prohibition on new internal combustion cars in 2035 has faced heavy pressure from the car sector and resistance from EU countries with significant car industries.

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

One external energy economics expert, who was unaffiliated with the research, described the analysis a “very useful addition” after a long period in which parts of the car industry argued there was too little data to properly assess real-world emissions.

“The results show, without question, that the difference between official and real-world PHEV fuel consumption and CO₂ output is significantly greater than for gasoline or conventional vehicles,” the expert stated. “Any policy adjustments regarding PHEVs should be made with extreme caution and in the light of that data.”