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Plug-in hybrid electric vehicles emit nearly five times more global warming emissions than lab-reported data show, according to a new analysis.

Growing Discrepancy Between Lab and Real-World CO2 Output

Data shows that PHEVs emit just 19% lower CO₂ than conventional gas and diesel cars, based on research conducted by a non-profit organization. That differs significantly with laboratory estimates, which assumed a three-quarters decrease in pollution.

Analysts studied data from onboard energy use meters of 800,000 cars sold in the EU between 2021 and 2023. They discovered that real-world CO₂ emissions from PHEVs in 2023 were 4.9 times higher than official estimates, increased from three and a half times in 2021.

“Real-world emissions are rising, while official figures are decreasing,” said a lead analyst participating in the study. “That gap is growing and creates a serious problem. As a result, PHEVs pollute nearly as much as gasoline vehicles.”

Key Reasons Driving the Discrepancy

Analysts linked the majority of the gap to overestimates of the “utility factor” – the ratio of kilometers travelled in battery power compared to total mileage. The team found that only a quarter of driving was done in electric mode, whereas lab estimates suggested over four-fifths.

Additionally, when operating in electric mode, emission levels were significantly higher than official projections. This occurred because EV motors were not strong sufficient to operate alone, leading to combustion motors burning fossil fuels for almost one-third of the distance covered in EV mode.

Policy and Financial Consequences

Based on calculations, the lowballing of PHEV emissions allowed four large carmaker companies to avoid more than €5bn in fines between 2021 and 2023, by artificially simplifying adherence with European Union fleet-average CO₂ targets.

Furthermore, drivers of PHEVs could pay about €500 more annually in running expenses than is estimated under lab conditions.

“The bold statements that automakers like to make about their PHEV cars are clearly way off the truth,” stated a transport analyst. “Consumers are being duped into believing that by buying a PHEV, they are benefiting the planet and saving money. Actually, PHEVs are little better than standard petrol and diesel cars in terms of fuel consumption, CO₂ production, and operating expenses.”

Political Debate and Industry Lobbying

Plug-in hybrid cars have recently been brought again into political discussions as automakers have pressed the European Union to relax CO₂ standards. A proposed ban on new internal combustion cars in 2035 has faced intense lobbying from the car industry and resistance from EU countries with significant automotive industries.

Several high-level officials have proposed plug-in hybrids as a possible “flexibility” option to introduce in the legislation.

An external energy economics expert, who was not involved with the research, described the analysis a “highly valuable addition” after a long period in which segments of the automotive industry argued there was insufficient information to accurately assess real-world CO2 output.

“These findings show, without question, that the difference between official and real-world PHEV energy use and CO₂ emissions is significantly greater than for petrol or conventional cars,” they said. “All regulatory adjustments concerning PHEVs should be made with utmost care and considering that data.”