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Plug-in hybrid cars emit nearly five times more planet-heating pollution than official data indicate, according to a recent report.

Growing Discrepancy Between Official and Real-World CO2 Output

Data reveals that PHEVs emit only one-fifth less CO₂ than traditional petrol and diesel cars, based on research conducted by a advocacy group. That contrasts sharply with laboratory estimates, which assumed a 75% decrease in emissions.

Researchers examined information from onboard fuel consumption meters of eight hundred thousand vehicles sold in the EU between 2021 and 2023. They found that actual CO₂ output from PHEVs in 2023 were nearly five times higher than official figures, increased from 3.5 times in 2021.

“Actual emissions are increasing, while lab-reported figures are decreasing,” said a lead researcher participating in the report. “That discrepancy is growing and poses a serious problem. Consequently, PHEVs emit nearly as heavily as petrol cars.”

Primary Reasons Behind the Emissions Gap

Analysts attributed the majority of the gap to overestimates of the “electric driving share” – the ratio of kilometers driven in battery power compared to overall distance. They found that only a quarter of travel was done in electric mode, whereas official estimates suggested over four-fifths.

Additionally, when operating in EV mode, pollution amounts were significantly higher than official estimates. This happened because EV motors were not strong enough to function independently, resulting to combustion motors burning fossil fuels for nearly a third of the distance completed in electric mode.

Policy and Economic Implications

Based on calculations, the underestimation of PHEV emissions enabled several major carmaker groups to escape over €5bn in penalties from 2021 and 2023, by artificially simplifying compliance with EU fleet-average CO₂ standards.

Additionally, drivers of PHEVs would spend about €500 extra per year in operating costs than would be assumed under lab tests.

“The strong claims that automakers often promote about their plug-in hybrid vehicles are clearly far from the truth,” stated a transport expert. “Consumers are being duped into believing that by purchasing a PHEV, they are helping the environment and saving money. In reality, PHEVs are little improved than regular gas and diesel vehicles in terms of energy consumption, CO₂ emissions, and operating costs.”

Political Debate and Industry Lobbying

Hybrid vehicles have lately been brought again into policy debates as carmakers have lobbied the EU to weaken CO₂ targets. A proposed ban on sales of new internal combustion vehicles in 2035 has faced intense lobbying from the car sector and opposition from member states with significant car industries.

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

One independent energy economics specialist, who was unaffiliated with the study, described the analysis a “highly valuable addition” after a long period in which parts of the automotive industry argued there was insufficient data to properly assess actual emissions.

“These findings demonstrate, beyond any doubt, that the gap in official and real-world PHEV fuel consumption and CO₂ output is significantly greater than for gasoline or diesel cars,” the expert said. “All regulatory adjustments concerning PHEVs should be made with extreme caution and in the light of this evidence.”