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Plug-in hybrid electric vehicles emit almost 5x greater global warming pollution than lab-reported data show, according to a new analysis.

Widening Discrepancy Between Lab and Real-World CO2 Output

Data reveals that PHEVs release just one-fifth less CO₂ than traditional petrol and diesel cars, according to research conducted by a advocacy group. That differs sharply with lab estimates, which suggested a three-quarters decrease in pollution.

Researchers studied data from in-vehicle fuel consumption monitors of 800,000 vehicles registered in Europe between 2021 and 2023. They discovered that actual CO₂ output from PHEVs in 2023 were nearly five times greater than official estimates, up from three and a half times in 2021.

“Actual CO2 output are increasing, while official emissions are falling,” said a lead analyst involved in the study. “That gap is growing and poses a significant problem. Consequently, PHEVs emit nearly as heavily as petrol vehicles.”

Key Factors Behind the Discrepancy

Researchers attributed the majority of the gap to inflated estimates of the “utility factor” – the percentage of miles travelled in electric power compared to overall distance. They determined that just a quarter of driving was completed in EV mode, while lab estimates suggested over four-fifths.

Additionally, when operating in EV mode, emission levels were significantly higher than lab estimates. This occurred because EV motors were not strong enough to operate alone, leading to combustion motors burning fossil fuels for nearly a 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 over €5bn in fines from 2021 and 2023, by artificially easing compliance with EU average fleet CO₂ targets.

Furthermore, drivers of PHEVs would spend about €500 more annually in running costs than would be estimated under lab conditions.

“The strong statements that manufacturers often promote about their plug-in hybrid vehicles are obviously 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. In reality, PHEVs are only slightly improved than standard gas and diesel cars in terms of energy use, CO₂ emissions, and operating expenses.”

Policy Discussion and Industry Pressure

Plug-in hybrid cars have lately been brought again into policy discussions as carmakers have pressed the European Union to relax CO₂ targets. A planned prohibition on sales of new combustion engine vehicles in 2035 has faced heavy lobbying from the automotive sector and resistance from EU countries with large automotive industries.

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

One independent energy policy expert, 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 information to properly assess real-world CO2 output.

“These findings show, beyond any doubt, that the difference in lab and actual PHEV energy use and CO₂ emissions is significantly larger than for gasoline or diesel vehicles,” the expert said. “Any policy adjustments concerning PHEVs should be implemented with extreme caution and in the light of this data.”