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Plug-in hybrid cars emit nearly five times greater global warming pollution than lab-reported figures indicate, as per a new analysis.

Widening Discrepancy Between Lab and Real-World CO2 Output

Data shows that PHEVs emit just 19% less CO₂ than traditional gas and diesel cars, according to analysis carried out by a non-profit group. This contrasts significantly with lab estimates, which assumed a three-quarters reduction in emissions.

Researchers examined information from onboard fuel consumption monitors of eight hundred thousand vehicles sold in Europe from 2021 and 2023. The team discovered that real-world CO₂ emissions from PHEVs in 2023 were nearly five times greater than official figures, increased from three and a half times in 2021.

“Real-world CO2 output are rising, while official figures are decreasing,” said a senior researcher involved in the study. “That discrepancy is growing and creates a serious issue. Consequently, PHEVs pollute almost as heavily as petrol vehicles.”

Primary Factors Behind the Emissions Gap

Researchers attributed the majority of the gap to inflated estimates of the “electric driving share” – the percentage of kilometers travelled in battery power relative to overall distance. The team determined that only a quarter of driving was completed in EV mode, while official estimates assumed 84%.

Even, when operating in electric mode, pollution levels were significantly higher than lab projections. That happened because electric motors were insufficiently powerful enough to function alone, resulting to engines using gasoline for nearly one-third of the travel covered in electric mode.

Regulatory and Financial Implications

According to estimates, the underestimation of PHEV CO2 output enabled several major carmaker groups to escape more than €5bn in fines between 2021 and 2023, by falsely simplifying adherence with EU average fleet CO₂ standards.

Additionally, drivers of PHEVs would spend about €500 more per year in running costs than is assumed under lab conditions.

“The strong claims that manufacturers often promote about their PHEV cars are clearly way off the mark,” stated a transport analyst. “Buyers are being misled into thinking that by purchasing a PHEV, they are benefiting the planet and saving costs. Actually, PHEVs are only slightly improved than standard petrol and diesel vehicles in terms of energy consumption, CO₂ production, and running expenses.”

Policy Debate and Industry Pressure

Plug-in hybrid vehicles have recently been drawn again into political debates as automakers have pressed the European Union to weaken CO₂ targets. A planned ban on new internal combustion cars in 2035 has faced intense lobbying from the car industry and opposition from member states with significant car industries.

Some senior officials have suggested plug-in hybrids as a possible “compromise” solution to introduce in the regulation.

One independent energy economics specialist, who was not involved with the research, called the report a “highly valuable contribution” after years in which parts of the automotive sector claimed there was insufficient data to properly assess actual emissions.

“These findings demonstrate, beyond any doubt, that the difference in official and actual PHEV fuel consumption and CO₂ emissions is significantly larger than for gasoline or diesel vehicles,” they said. “Any policy adjustments regarding PHEVs should be made with utmost caution and in the light of this data.”