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Plug-in hybrid cars release nearly five times greater global warming emissions than lab-reported data show, according to a new analysis.

Widening Gap In Lab and Real-World Emissions

Data reveals that PHEVs emit only one-fifth less CO₂ than conventional petrol and diesel cars, based on analysis conducted by a non-profit organization. This contrasts sharply with laboratory tests, which suggested a 75% decrease in emissions.

Researchers examined information from onboard energy use monitors of 800,000 vehicles sold in the EU from 2021 and 2023. They found that real-world CO₂ output from PHEVs in 2023 were 4.9 times greater than official figures, up from three and a half times in 2021.

“Real-world CO2 output are rising, while lab-reported figures are decreasing,” stated a senior researcher participating in the report. “This gap is growing and poses a significant issue. Consequently, PHEVs pollute almost as much as gasoline vehicles.”

Key Reasons Behind the Emissions Gap

Researchers attributed most of the gap to overestimates of the “electric driving share” – the ratio of kilometers travelled in battery mode relative to total mileage. They found that only a quarter of travel was completed in electric mode, while lab assumptions suggested over four-fifths.

Even, when operating in EV mode, emission levels were significantly higher than lab projections. That happened because EV motors were insufficiently powerful enough to operate independently, leading to engines using fossil fuels for almost a third of the distance completed in EV mode.

Regulatory and Economic Consequences

According to estimates, the underestimation of PHEV emissions allowed several large carmaker companies to avoid more than €5bn in penalties between 2021 and 2023, by falsely easing adherence with EU average fleet CO₂ targets.

Additionally, drivers of PHEVs could pay approximately €500 more annually in running costs than would be estimated under lab tests.

“The strong statements that automakers like to make about their PHEV vehicles are obviously far from the mark,” commented a automotive analyst. “Buyers are being misled into thinking that by purchasing a PHEV, they are helping the planet and cutting money. Actually, PHEVs are little improved than standard petrol and diesel cars in terms of energy consumption, CO₂ production, and operating costs.”

Policy Discussion and Automotive Pressure

Hybrid vehicles have recently been brought back into political discussions as carmakers have lobbied the EU to weaken CO₂ standards. A planned ban on sales of new internal combustion cars in 2035 has faced heavy lobbying from the automotive industry and resistance from EU countries with significant automotive industries.

Some senior politicians have suggested PHEVs as a possible “flexibility” solution to include in the legislation.

One external energy policy expert, who was not involved with the research, described the report a “very useful contribution” after years in which parts of the automotive industry argued there was insufficient information to properly assess actual emissions.

“The results demonstrate, 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 said. “All policy changes concerning PHEVs should be implemented with utmost caution and considering this evidence.”