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Plug-in hybrid electric vehicles produce nearly 5x greater global warming pollution than official figures indicate, according to a new report.

Growing Gap Between Official and Real-World CO2 Output

Data reveals that PHEVs release just 19% less CO₂ than traditional gas and diesel vehicles, according to research conducted by a non-profit group. That differs sharply with laboratory estimates, which suggested a 75% reduction in emissions.

Researchers examined data from in-vehicle fuel consumption monitors of 800,000 vehicles sold in the EU between 2021 and 2023. The team discovered that real-world CO₂ output from PHEVs in 2023 were nearly five times higher than official estimates, up from three and a half times in 2021.

“Actual CO2 output are rising, while lab-reported emissions are falling,” stated a lead researcher involved in the study. “That gap is widening and poses a serious issue. As a result, PHEVs pollute nearly as heavily as petrol cars.”

Primary Reasons Behind the Emissions Gap

Researchers attributed most of the gap to overestimates of the “utility factor” – the percentage of miles travelled in battery power relative to overall mileage. They determined that only a quarter of driving was done in EV mode, while official estimates assumed over four-fifths.

Even, when running in electric mode, pollution amounts were well above official projections. That occurred because electric motors were insufficiently powerful enough to function alone, resulting to engines burning gasoline for nearly one-third of the distance covered in EV mode.

Regulatory and Economic Consequences

According to estimates, the underestimation of PHEV CO2 output enabled four major carmaker companies to avoid more than €5bn in penalties from 2021 and 2023, by artificially simplifying compliance with European Union fleet-average CO₂ standards.

Furthermore, drivers of PHEVs would pay about €500 more per year in running costs than is estimated under laboratory conditions.

“The strong claims that automakers like to make about their plug-in hybrid vehicles are clearly way off the mark,” stated a automotive expert. “Consumers are being misled into believing that by purchasing a PHEV, they are helping the planet and saving costs. Actually, PHEVs are little better than regular petrol and diesel vehicles in terms of energy use, CO₂ emissions, and operating expenses.”

Political Debate and Industry Pressure

Plug-in hybrid vehicles have recently been brought back into policy debates as automakers have pressed the European Union to relax CO₂ standards. A planned ban on sales of new combustion engine cars in 2035 has faced heavy lobbying from the car sector and opposition from member states with large car industries.

Several senior officials have proposed plug-in hybrids as a possible “flexibility” option to introduce in the regulation.

One independent energy economics specialist, who was unaffiliated with the research, described the report a “highly valuable addition” after years in which parts of the automotive industry claimed there was insufficient information to properly assess real-world CO2 output.

“These findings demonstrate, without question, that the gap in official and actual PHEV energy use and CO₂ output is much, much larger than for gasoline or diesel cars,” they said. “All policy changes concerning PHEVs should be made with extreme care and in the light of that data.”