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Plug-in hybrid cars release nearly five times greater planet-heating pollution than lab-reported figures show, according to a new analysis.

Growing Discrepancy Between Lab and Real-World CO2 Output

Data shows that PHEVs release only one-fifth lower CO₂ than traditional gas and diesel cars, based on analysis conducted by a non-profit group. That differs sharply with laboratory tests, which assumed a three-quarters decrease in emissions.

Researchers studied data from onboard fuel consumption meters of 800,000 cars registered in Europe between 2021 and 2023. The team discovered that real-world CO₂ emissions from PHEVs in 2023 were 4.9 times greater than official estimates, increased from 3.5 times in 2021.

“Real-world CO2 output are rising, while lab-reported figures are falling,” stated a lead analyst participating in the report. “That discrepancy is widening and creates a serious problem. Consequently, PHEVs emit nearly as heavily as petrol vehicles.”

Primary Factors Behind the Emissions Gap

Researchers linked the majority of the gap to overestimates of the “electric driving share” – the percentage of kilometers travelled in electric mode relative to total mileage. They found that just a quarter of travel was done in electric mode, while lab estimates suggested 84%.

Even, when running in EV mode, pollution levels were well above lab estimates. This occurred because EV motors were not strong enough to operate independently, resulting to engines burning fossil fuels for almost one-third of the travel completed in EV mode.

Regulatory and Financial Consequences

Based on calculations, the underestimation of PHEV emissions enabled four large automaker groups to escape over €5bn in penalties between 2021 and 2023, by falsely easing adherence with EU average fleet CO₂ standards.

Additionally, drivers of PHEVs would pay approximately €500 extra annually in operating expenses than is assumed under laboratory tests.

“The strong claims that automakers often promote about their plug-in hybrid vehicles are clearly far from the mark,” stated a transport analyst. “Buyers are being duped into believing that by buying a PHEV, they are helping the environment and saving costs. In reality, PHEVs are little better than regular petrol and diesel cars in terms of energy use, CO₂ production, and running expenses.”

Political Debate and Industry Lobbying

Plug-in hybrid cars have lately been drawn again into political discussions as carmakers have pressed the European Union to weaken CO₂ standards. A proposed prohibition on sales of new combustion engine vehicles in 2035 has faced heavy pressure from the automotive industry and opposition from member states with large car manufacturing.

Some high-level officials have proposed plug-in hybrids as a potential “compromise” option to include in the regulation.

An independent energy economics expert, who was unaffiliated with the study, described the report a “very useful addition” after a long period in which segments of the car sector argued there was too little information to properly evaluate actual emissions.

“These findings demonstrate, beyond any doubt, that the gap in official and real-world PHEV energy use and CO₂ output is significantly greater than for gasoline or conventional vehicles,” the expert stated. “Any regulatory adjustments concerning PHEVs should be implemented with utmost caution and considering that evidence.”