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Plug-in hybrid electric vehicles release almost 5x more global warming emissions than official data show, according to a recent report.

Widening Gap Between Lab and Actual Emissions

Data reveals that PHEVs release just 19% lower CO₂ than conventional gas and diesel vehicles, according to research carried out by a non-profit group. That contrasts sharply with lab tests, which assumed a three-quarters decrease in emissions.

Researchers examined data from in-vehicle energy use monitors of eight hundred thousand cars registered in Europe from 2021 and 2023. They found that actual CO₂ output from PHEVs in 2023 were nearly five times higher than lab estimates, up from 3.5 times in 2021.

“Actual emissions are increasing, while official emissions are decreasing,” stated a lead researcher participating in the study. “This discrepancy is widening and poses a serious problem. As a result, PHEVs pollute nearly as heavily as gasoline cars.”

Key Reasons Behind the Discrepancy

Researchers attributed the majority of the difference to inflated estimates of the “electric driving share” – the ratio of miles driven in electric power compared to overall mileage. The team determined that only a quarter of driving was completed in EV mode, whereas lab assumptions assumed over four-fifths.

Even, when running in EV mode, emission levels were well above official projections. That happened because EV motors were not strong sufficient to operate alone, leading to combustion motors using gasoline for nearly one-third of the distance completed in electric mode.

Regulatory and Financial Implications

According to calculations, the lowballing of PHEV emissions allowed four large automaker companies to escape more than €5bn in fines between 2021 and 2023, by falsely easing compliance with European Union fleet-average CO₂ targets.

Additionally, drivers of PHEVs could pay approximately €500 extra per year in running costs than is estimated under lab tests.

“The bold claims that manufacturers often promote about their PHEV cars are clearly way off the mark,” stated a automotive analyst. “Buyers are being misled into thinking that by purchasing a PHEV, they are helping the planet and cutting costs. Actually, PHEVs are little improved than standard gas and diesel vehicles in terms of energy consumption, CO₂ emissions, and operating expenses.”

Policy Debate and Automotive Lobbying

Plug-in hybrid cars have lately been brought back into political discussions as automakers have lobbied the European Union to relax CO₂ standards. A planned ban on new internal combustion cars in 2035 has faced heavy pressure from the car sector and resistance from EU countries with significant automotive industries.

Some senior politicians have proposed plug-in hybrids as a possible “compromise” option to include in the regulation.

One external energy policy expert, who was not involved with the research, described the report a “very useful addition” after a long period in which segments of the car sector argued there was insufficient data to accurately assess real-world emissions.

“The results demonstrate, without question, that the gap between official and real-world PHEV energy use and CO₂ emissions is significantly larger than for gasoline or diesel vehicles,” they stated. “All regulatory adjustments regarding PHEVs should be implemented with extreme caution and considering that evidence.”