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Plug-in hybrid cars emit nearly five times greater global warming emissions than lab-reported data show, according to a recent analysis.

Growing Gap Between Lab and Actual Emissions

Data reveals that PHEVs emit only 19% less CO₂ than conventional gas and diesel vehicles, according to research carried out by a advocacy organization. That contrasts sharply with lab tests, which suggested a 75% reduction in emissions.

Analysts examined information from in-vehicle fuel consumption monitors of 800,000 cars registered in the EU between 2021 and 2023. The team found that actual CO₂ output from PHEVs in 2023 were nearly five times greater than official estimates, increased from 3.5 times in 2021.

“Real-world emissions are increasing, while lab-reported emissions are falling,” said a senior analyst involved in the report. “This gap is growing and poses a serious issue. Consequently, PHEVs pollute nearly as heavily as gasoline vehicles.”

Key Reasons Behind the Discrepancy

Researchers linked most of the difference to overestimates of the “electric driving share” – the percentage of miles driven in electric mode relative to total distance. They found that just 27% of travel was completed in EV mode, while official assumptions suggested over four-fifths.

Additionally, when operating in electric mode, pollution amounts were significantly higher than lab estimates. That occurred because EV motors were insufficiently powerful enough to function alone, leading to engines burning gasoline for almost a third of the travel completed in EV mode.

Policy and Financial Implications

Based on estimates, the underestimation of PHEV emissions allowed four large carmaker companies to avoid more than €5bn in fines from 2021 and 2023, by artificially simplifying compliance with EU average fleet CO₂ standards.

Furthermore, owners of PHEVs would pay approximately €500 more annually in running costs than would be estimated under lab tests.

“The bold statements that manufacturers like to make about their plug-in hybrid cars are obviously far from the truth,” stated a transport expert. “Buyers are being duped into thinking that by purchasing a PHEV, they are benefiting the environment and saving costs. Actually, PHEVs are little improved than standard petrol and diesel cars in terms of fuel consumption, CO₂ production, and operating expenses.”

Political Debate and Industry Lobbying

Hybrid cars have recently been drawn back into policy debates as carmakers have pressed the European Union to weaken CO₂ standards. A proposed ban on new combustion engine cars in 2035 has faced intense lobbying from the automotive industry and opposition from EU countries with significant car manufacturing.

Several senior officials have proposed PHEVs as a potential “flexibility” option to introduce in the legislation.

An external energy economics specialist, who was unaffiliated with the study, called the analysis a “highly valuable contribution” after a long period in which parts of the car industry claimed there was insufficient data to accurately assess actual CO2 output.

“These findings show, without question, that the gap in official and real-world PHEV energy use and CO₂ emissions is significantly larger than for petrol or conventional vehicles,” the expert stated. “All policy adjustments regarding PHEVs should be made with utmost care and in the light of that data.”