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Plug-in hybrid cars release almost 5x greater global warming emissions than official data indicate, according to a new report.

Widening Gap Between Lab and Actual CO2 Output

Statistics reveals that PHEVs release only one-fifth less CO₂ than traditional petrol and diesel cars, according to analysis carried out by a non-profit group. That contrasts sharply with lab estimates, which assumed a three-quarters decrease in emissions.

Researchers studied data from onboard fuel consumption monitors of 800,000 cars sold in Europe between 2021 and 2023. They found that real-world CO₂ emissions from PHEVs in 2023 were nearly five times higher than official estimates, up from 3.5 times in 2021.

“Real-world CO2 output are increasing, while official emissions are decreasing,” said a lead researcher participating in the report. “This discrepancy is widening and creates a significant issue. Consequently, PHEVs pollute almost as heavily as gasoline vehicles.”

Key Reasons Behind the Emissions Gap

Researchers attributed the majority of the gap to inflated estimates of the “utility factor” – the ratio of miles travelled in electric mode compared to total mileage. The team found that just 27% of driving was completed in electric mode, whereas official estimates assumed 84%.

Additionally, when operating in EV mode, pollution amounts were significantly higher than official estimates. That occurred because electric motors were insufficiently powerful sufficient to operate independently, resulting to combustion motors using fossil fuels for nearly a third of the distance completed in electric mode.

Regulatory and Economic Consequences

According to estimates, the underestimation of PHEV emissions allowed four large automaker groups to avoid over €5bn in penalties between 2021 and 2023, by falsely simplifying adherence with EU average fleet CO₂ targets.

Additionally, drivers of PHEVs could spend about €500 more per year in running expenses than is assumed under laboratory conditions.

“The strong statements that manufacturers like to make about their PHEV cars are clearly far from the truth,” commented a transport analyst. “Buyers are being duped into thinking that by purchasing a PHEV, they are helping the environment and cutting money. Actually, PHEVs are only slightly better than regular gas and diesel vehicles in terms of energy consumption, CO₂ production, and operating expenses.”

Policy Debate and Automotive Lobbying

Plug-in hybrid vehicles have lately been brought again into policy discussions as automakers have lobbied the European Union to relax CO₂ targets. A proposed ban on new combustion engine vehicles in 2035 has faced heavy pressure from the car sector and opposition from EU countries with significant automotive manufacturing.

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

An external energy economics specialist, who was unaffiliated with the research, described the analysis a “highly valuable addition” after a long period in which segments of the automotive sector claimed there was insufficient data to accurately evaluate actual emissions.

“These findings demonstrate, beyond any doubt, that the difference between official and real-world PHEV fuel consumption and CO₂ emissions is significantly greater than for gasoline or diesel cars,” the expert said. “Any regulatory changes regarding PHEVs should be implemented with extreme care and considering this evidence.”