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Plug-in hybrid cars produce almost 5x more global warming pollution than lab-reported data indicate, according to a new analysis.

Widening Discrepancy Between Official and Actual Emissions

Statistics shows that PHEVs emit just one-fifth less CO₂ than traditional petrol and diesel cars, based on analysis carried out by a non-profit group. This contrasts sharply with laboratory tests, which assumed a three-quarters reduction in emissions.

Researchers examined data from in-vehicle energy use meters of 800,000 cars sold in the EU from 2021 and 2023. The team found that real-world CO₂ emissions from PHEVs in 2023 were nearly five times greater than lab figures, increased from 3.5 times in 2021.

“Real-world CO2 output are rising, while lab-reported figures are decreasing,” stated a senior analyst involved in the study. “This discrepancy is growing and poses a serious issue. As a result, PHEVs emit almost as heavily as gasoline cars.”

Key Factors Driving the Emissions Gap

Analysts linked most of the gap to overestimates of the “electric driving share” – the ratio of kilometers driven in battery power relative to overall mileage. The team found that only 27% of driving was completed in electric mode, whereas official estimates assumed over four-fifths.

Additionally, when operating in electric mode, emission levels were significantly higher than official projections. This occurred because electric motors were not strong sufficient to operate independently, resulting to combustion motors using gasoline for nearly one-third of the distance covered in EV mode.

Policy and Financial Implications

According to estimates, the lowballing of PHEV emissions allowed four major carmaker groups to avoid over €5bn in penalties from 2021 and 2023, by falsely simplifying compliance with European Union fleet-average CO₂ standards.

Furthermore, owners of PHEVs would pay approximately €500 extra per year in operating costs than would be estimated under lab tests.

“The bold claims that manufacturers like to make about their PHEV vehicles are obviously far from the truth,” stated a transport analyst. “Consumers are being duped into believing that by purchasing a PHEV, they are benefiting the planet and cutting costs. Actually, PHEVs are only slightly improved than regular petrol and diesel vehicles in terms of fuel use, CO₂ production, and operating costs.”

Political Debate and Industry Lobbying

Plug-in hybrid vehicles have recently been brought back into political debates as automakers have lobbied the EU to relax CO₂ standards. A planned ban on new combustion engine cars in 2035 has faced heavy pressure from the car sector and resistance from member states with large car manufacturing.

Several senior officials have proposed PHEVs as a possible “compromise” option to introduce in the regulation.

An independent energy economics specialist, who was unaffiliated with the study, described the report a “highly valuable addition” after years in which segments of the car sector claimed there was insufficient data to accurately evaluate actual emissions.

“These findings demonstrate, without question, that the difference in official and real-world PHEV fuel consumption and CO₂ output is much, much larger than for petrol or conventional vehicles,” the expert stated. “All regulatory adjustments regarding PHEVs should be implemented with extreme care and considering this data.”