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PHEVs emit nearly 5x more global warming pollution than lab-reported data indicate, according to a new analysis.

Growing Discrepancy In Official and Actual CO2 Output

Data shows that PHEVs release just 19% lower CO₂ than traditional gas and diesel cars, according to analysis conducted by a non-profit group. That contrasts significantly with laboratory estimates, which suggested a 75% reduction in emissions.

Researchers examined information from onboard fuel consumption meters of 800,000 vehicles registered in Europe between 2021 and 2023. They found that real-world CO₂ output from PHEVs in 2023 were nearly five times higher than lab figures, up from 3.5 times in 2021.

“Real-world CO2 output are rising, while lab-reported figures are falling,” stated a lead analyst involved in the study. “That discrepancy is growing and poses a serious problem. As a result, PHEVs pollute almost as heavily as petrol vehicles.”

Primary Factors Driving the Emissions Gap

Researchers attributed the majority of the difference to inflated estimates of the “electric driving share” – the ratio of miles travelled in battery power relative to total mileage. They found that only 27% of driving was completed in EV mode, while lab assumptions assumed 84%.

Even, when running in EV mode, pollution levels were significantly higher than official estimates. That occurred because electric motors were not strong enough to operate alone, resulting to engines burning gasoline for nearly one-third of the distance completed in EV mode.

Policy and Economic Consequences

Based on calculations, the underestimation of PHEV emissions enabled four large carmaker groups to escape more than €5bn in fines from 2021 and 2023, by falsely easing adherence with European Union fleet-average CO₂ standards.

Furthermore, owners of PHEVs would spend about €500 extra annually in operating costs than would be estimated under lab conditions.

“The strong statements that manufacturers often promote about their plug-in hybrid vehicles are clearly far from the truth,” commented a transport expert. “Buyers are being misled into thinking that by buying a PHEV, they are helping the planet and saving costs. Actually, PHEVs are little better than standard gas and diesel cars in terms of fuel consumption, CO₂ emissions, and operating costs.”

Political Debate and Automotive Pressure

Plug-in hybrid cars have recently been brought back into policy discussions as carmakers have lobbied the EU to weaken CO₂ standards. A proposed ban on sales of new combustion engine cars in 2035 has faced heavy pressure from the car sector and opposition from member states with large car industries.

Several high-level officials have suggested PHEVs as a possible “compromise” solution to introduce in the legislation.

One independent energy economics specialist, who was unaffiliated with the research, called the analysis a “highly valuable contribution” after a long period in which segments of the automotive industry claimed there was insufficient data to properly assess actual emissions.

“The results demonstrate, beyond any doubt, that the gap in lab and actual PHEV fuel consumption and CO₂ output is much, much larger than for petrol or conventional vehicles,” the expert said. “All regulatory adjustments concerning PHEVs should be made with extreme care and in the light of this evidence.”