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Plug-in hybrid cars release almost 5x more global warming pollution than lab-reported data show, as per a recent analysis.

Growing Discrepancy Between Official and Real-World Emissions

Data shows that PHEVs release just 19% less CO₂ than traditional gas and diesel cars, based on analysis conducted by a non-profit organization. That contrasts sharply with laboratory tests, which suggested a 75% decrease in emissions.

Analysts examined data from in-vehicle energy use meters 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 lab estimates, up from 3.5 times in 2021.

“Actual CO2 output are rising, while official figures are falling,” said a lead researcher participating in the report. “This discrepancy is widening and creates a serious problem. As a result, PHEVs pollute almost as heavily as petrol vehicles.”

Primary Reasons Behind the Discrepancy

Researchers linked the majority of the difference to overestimates of the “electric driving share” – the percentage of miles driven in electric power compared to overall mileage. The team found that just 27% of travel was done in electric mode, while lab estimates assumed 84%.

Additionally, when operating in electric mode, pollution levels were well above lab estimates. That occurred because EV motors were not strong enough to operate alone, leading to engines burning fossil fuels for nearly one-third of the distance covered in EV mode.

Regulatory and Economic Implications

According to estimates, the underestimation of PHEV emissions enabled several major automaker groups to avoid over €5bn in penalties between 2021 and 2023, by artificially simplifying adherence with European Union fleet-average CO₂ standards.

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

“The bold claims that manufacturers often promote about their plug-in hybrid vehicles are clearly way off the truth,” stated a automotive analyst. “Buyers are being duped into thinking that by purchasing a PHEV, they are benefiting the planet and cutting money. In reality, PHEVs are little improved than standard petrol and diesel cars in terms of fuel use, CO₂ emissions, and running costs.”

Political Debate and Industry Lobbying

Plug-in hybrid vehicles have recently been brought again into political discussions as automakers have lobbied the European Union to weaken CO₂ standards. A proposed prohibition on sales of new combustion engine vehicles in 2035 has faced intense pressure from the car industry and opposition from EU countries with large car industries.

Some high-level politicians have proposed PHEVs as a possible “compromise” solution to include in the regulation.

One external energy policy specialist, who was unaffiliated with the study, called the analysis a “highly valuable addition” after years in which parts of the automotive industry claimed there was insufficient information to properly evaluate real-world CO2 output.

“These findings demonstrate, beyond any doubt, that the gap in lab and real-world PHEV energy use and CO₂ emissions is much, much larger than for petrol or diesel vehicles,” they stated. “Any regulatory changes regarding PHEVs should be made with extreme caution and considering this evidence.”