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Plug-in hybrid cars produce nearly five times greater global warming emissions than official data show, according to a recent analysis.

Growing Discrepancy Between Lab and Real-World Emissions

Data reveals that PHEVs release just 19% lower CO₂ than conventional petrol and diesel cars, according to analysis conducted by a non-profit group. That contrasts sharply with lab estimates, which suggested a three-quarters reduction in emissions.

Researchers examined data from onboard energy use meters of 800,000 cars registered in the EU from 2021 and 2023. The team found that real-world CO₂ emissions from PHEVs in 2023 were 4.9 times greater than lab figures, up from 3.5 times in 2021.

“Actual CO2 output are increasing, while lab-reported emissions are decreasing,” said a senior analyst involved in the report. “That discrepancy is widening and poses a significant issue. As a result, PHEVs emit almost as heavily as gasoline vehicles.”

Key Reasons Behind the Emissions Gap

Researchers attributed the majority of the difference to overestimates of the “utility factor” – the percentage of miles travelled in electric mode compared to total mileage. They found that only 27% of driving was completed in electric mode, while lab estimates assumed 84%.

Additionally, when running in electric mode, emission amounts were significantly higher than lab estimates. That happened because EV motors were not strong enough to operate independently, resulting to combustion motors burning gasoline for nearly a third of the travel completed in EV mode.

Regulatory and Economic Implications

According to calculations, the underestimation of PHEV CO2 output enabled four major automaker companies to avoid more than €5bn in fines from 2021 and 2023, by artificially simplifying adherence with European Union average fleet CO₂ targets.

Additionally, drivers of PHEVs could spend about €500 extra per year in running expenses than would be estimated under laboratory conditions.

“The strong claims that automakers often promote about their plug-in hybrid vehicles are obviously way off the mark,” commented a transport analyst. “Consumers are being duped into believing that by purchasing a PHEV, they are helping the environment and cutting money. Actually, PHEVs are little improved than regular petrol and diesel vehicles in terms of fuel use, CO₂ production, and operating costs.”

Policy Debate and Industry Lobbying

Hybrid vehicles have recently been brought again into policy discussions as carmakers have pressed the European Union to relax CO₂ standards. A proposed prohibition on sales of new internal combustion cars in 2035 has faced intense pressure from the automotive industry and opposition from EU countries with significant car manufacturing.

Some senior officials have proposed PHEVs as a potential “compromise” option to introduce in the legislation.

An external energy policy specialist, who was not involved with the research, called the report a “very useful addition” after years in which parts of the automotive sector argued there was too little information to properly assess real-world emissions.

“The results demonstrate, beyond any doubt, that the gap between official and actual PHEV energy use and CO₂ output is much, much greater than for gasoline or conventional cars,” they said. “All regulatory changes regarding PHEVs should be implemented with utmost care and considering this data.”