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

Growing Gap Between Official and Real-World CO2 Output

Data shows that PHEVs emit just 19% less CO₂ than conventional gas and diesel vehicles, according to analysis carried out by a advocacy organization. That contrasts sharply with laboratory estimates, which assumed a 75% decrease in pollution.

Researchers studied information from onboard fuel consumption monitors of eight hundred thousand vehicles registered in the EU between 2021 and 2023. They found that real-world CO₂ output from PHEVs in 2023 were nearly five times higher than official figures, increased from three and a half times in 2021.

“Real-world emissions are rising, while lab-reported figures are decreasing,” said a senior analyst participating in the report. “That gap is growing and creates a significant issue. As a result, PHEVs pollute almost as much as petrol vehicles.”

Primary Factors Behind the Emissions Gap

Researchers attributed most of the difference to overestimates of the “electric driving share” – the percentage of miles travelled in battery power compared to total distance. The team found that just a quarter of travel was completed in electric mode, while official estimates assumed over four-fifths.

Additionally, when running in electric mode, emission levels were significantly higher than lab projections. This happened because electric motors were not strong sufficient to operate alone, leading to combustion motors using gasoline for nearly one-third of the distance completed in electric mode.

Policy and Economic Consequences

According to calculations, the underestimation of PHEV emissions allowed four major automaker groups to avoid over €5bn in fines between 2021 and 2023, by falsely easing adherence with EU fleet-average CO₂ standards.

Furthermore, owners of PHEVs would pay about €500 more annually in operating costs than is estimated under lab tests.

“The strong claims that automakers often promote about their plug-in hybrid cars are obviously way off the mark,” commented a transport analyst. “Consumers are being misled into believing that by purchasing a PHEV, they are benefiting the planet and saving costs. In reality, PHEVs are little better than standard gas and diesel cars in terms of fuel use, CO₂ emissions, and running expenses.”

Political Debate and Automotive Pressure

Plug-in hybrid vehicles have recently been brought again into political debates as automakers have lobbied the European Union to weaken CO₂ standards. A planned ban on new internal combustion vehicles in 2035 has faced heavy pressure from the automotive industry and resistance from EU countries with significant automotive manufacturing.

Some high-level officials have suggested PHEVs as a potential “flexibility” option to include in the legislation.

One independent energy policy specialist, who was unaffiliated with the study, described the report a “very useful contribution” after years in which segments of the car industry argued there was too little information to properly evaluate actual CO2 output.

“These findings show, without question, that the difference between official and actual PHEV fuel consumption and CO₂ output is significantly greater than for gasoline or diesel vehicles,” the expert stated. “All regulatory adjustments concerning PHEVs should be made with extreme care and considering that evidence.”