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PHEVs emit nearly five times more global warming pollution than official figures indicate, according to a recent report.

Growing Discrepancy In Lab and Real-World Emissions

Statistics reveals that PHEVs release just one-fifth less CO₂ than conventional gas and diesel cars, based on analysis conducted by a advocacy organization. That differs sharply with lab tests, which suggested a 75% reduction in emissions.

Researchers studied information from in-vehicle energy use monitors of 800,000 cars sold in the EU between 2021 and 2023. The team discovered that real-world CO₂ emissions from PHEVs in 2023 were nearly five times higher than lab figures, increased from 3.5 times in 2021.

“Real-world emissions are increasing, while lab-reported figures are falling,” said a senior analyst involved in the report. “This discrepancy is growing and creates a serious problem. As a result, PHEVs pollute almost as much as petrol vehicles.”

Key Reasons Driving the Discrepancy

Researchers attributed the majority of the difference to overestimates of the “electric driving share” – the ratio of kilometers driven in battery power compared to total distance. They found that just 27% of driving was completed in electric mode, whereas official assumptions assumed over four-fifths.

Additionally, when running in EV mode, emission levels were well above lab projections. This happened because EV motors were insufficiently powerful enough to function independently, leading to combustion motors burning gasoline for nearly a third of the distance covered in EV mode.

Policy and Economic Implications

Based on calculations, the underestimation of PHEV CO2 output allowed several large carmaker companies to avoid more than €5bn in fines between 2021 and 2023, by falsely easing compliance with EU fleet-average CO₂ targets.

Additionally, owners of PHEVs would pay approximately €500 more per year in operating costs than would be estimated under lab tests.

“The strong statements that manufacturers often promote about their plug-in hybrid vehicles are clearly far from the truth,” commented a transport analyst. “Buyers are being duped into thinking that by buying a PHEV, they are helping the environment and saving costs. Actually, PHEVs are only slightly improved than standard gas and diesel cars in terms of fuel consumption, CO₂ production, and running expenses.”

Policy Debate and Automotive Pressure

Plug-in hybrid cars have recently been drawn back into policy debates as carmakers have lobbied the EU to weaken CO₂ standards. A proposed prohibition on new internal combustion cars in 2035 has faced intense pressure from the car industry and resistance from EU countries with significant car industries.

Some senior officials have proposed PHEVs as a possible “flexibility” option to include in the regulation.

One independent energy economics specialist, who was not involved with the study, described the analysis a “very useful addition” after years in which parts of the car sector claimed there was too little information to accurately assess actual CO2 output.

“These findings demonstrate, beyond any doubt, that the difference in lab and real-world PHEV energy use and CO₂ emissions is significantly greater than for gasoline or diesel cars,” the expert said. “Any policy changes concerning PHEVs should be made with extreme care and in the light of this data.”