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Plug-in hybrid electric vehicles produce almost 5x greater planet-heating emissions than official data show, according to a new report.

Widening Gap In Official and Real-World Emissions

Data shows that PHEVs emit only one-fifth less CO₂ than conventional gas and diesel cars, based on research conducted by a non-profit group. This contrasts sharply with laboratory estimates, which suggested a three-quarters decrease in emissions.

Researchers studied information from in-vehicle fuel consumption monitors of 800,000 cars sold in Europe between 2021 and 2023. The team discovered that actual CO₂ output from PHEVs in 2023 were 4.9 times higher than official figures, increased from 3.5 times in 2021.

“Actual CO2 output are rising, while official emissions are falling,” stated a lead researcher participating in the study. “This discrepancy is widening and poses a significant problem. Consequently, PHEVs pollute almost as heavily as gasoline vehicles.”

Primary Factors Driving the Discrepancy

Analysts linked most of the gap to inflated estimates of the “electric driving share” – the ratio of miles driven in battery power relative to total distance. They determined that only a quarter of driving was completed in electric mode, whereas lab estimates assumed over four-fifths.

Even, when operating in electric mode, emission amounts were significantly higher than official projections. That happened because electric motors were insufficiently powerful enough to function independently, leading to combustion motors burning fossil fuels for nearly one-third of the travel covered in EV mode.

Regulatory and Financial Implications

According to calculations, the underestimation of PHEV CO2 output allowed four large automaker groups to avoid over €5bn in fines between 2021 and 2023, by falsely simplifying compliance with European Union average fleet CO₂ targets.

Furthermore, owners of PHEVs could spend about €500 more per year in operating expenses than would be estimated under lab tests.

“The bold claims that automakers often promote about their PHEV vehicles are obviously far from the mark,” stated a automotive expert. “Consumers are being duped into believing that by buying a PHEV, they are benefiting the environment and cutting money. In reality, PHEVs are little better than standard gas and diesel vehicles in terms of energy consumption, CO₂ emissions, and running costs.”

Political Discussion and Automotive Lobbying

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

Some senior politicians have suggested plug-in hybrids as a potential “flexibility” option to introduce in the legislation.

One independent energy economics specialist, who was unaffiliated with the research, described the report a “highly valuable contribution” after years in which segments of the car sector argued there was too little data to accurately assess actual CO2 output.

“These findings demonstrate, without question, that the gap in lab and real-world PHEV energy use and CO₂ emissions is much, much larger than for gasoline or conventional cars,” the expert said. “All policy adjustments regarding PHEVs should be made with extreme caution and considering that evidence.”