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Plug-in hybrid electric vehicles produce almost five times greater global warming emissions than official data indicate, according to a new analysis.

Widening Gap In Official and Real-World Emissions

Data shows that PHEVs emit just 19% less CO₂ than traditional petrol and diesel vehicles, according to analysis carried out by a non-profit organization. This differs sharply with lab tests, which suggested a three-quarters reduction in emissions.

Analysts studied data from in-vehicle fuel consumption meters of 800,000 cars registered in the EU from 2021 and 2023. The team found that real-world CO₂ output from PHEVs in 2023 were nearly five times higher than official estimates, up from three and a half times in 2021.

“Real-world emissions are rising, while official emissions are decreasing,” said a lead analyst involved in the study. “This gap is widening and creates a serious problem. As a result, PHEVs emit almost as heavily as gasoline cars.”

Primary Reasons Driving the Emissions Gap

Researchers attributed most of the gap to overestimates of the “electric driving share” – the percentage of miles driven in battery power relative to overall mileage. The team determined that just 27% of travel was completed in electric mode, while lab estimates suggested over four-fifths.

Additionally, when operating in EV mode, emission levels were significantly higher than lab projections. That happened because electric motors were not strong enough to operate alone, leading to engines burning fossil fuels for almost one-third of the distance covered in EV mode.

Regulatory and Economic Consequences

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

Additionally, owners of PHEVs could spend about €500 more annually in operating costs than is assumed under lab tests.

“The bold statements that manufacturers often promote about their plug-in hybrid vehicles are clearly far from the mark,” commented a automotive expert. “Consumers are being duped into believing that by buying a PHEV, they are benefiting the planet and cutting costs. Actually, PHEVs are only slightly improved than regular petrol and diesel cars in terms of energy consumption, CO₂ production, and operating expenses.”

Policy Debate and Industry Pressure

Plug-in hybrid vehicles have recently been drawn back into policy debates as automakers have pressed the EU to relax CO₂ targets. A planned ban on sales of new internal combustion cars in 2035 has faced heavy lobbying from the automotive sector and resistance from EU countries with large car manufacturing.

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

One independent energy economics specialist, who was unaffiliated with the study, described the report a “very useful contribution” after years in which parts of the automotive industry argued there was too little data to properly evaluate actual CO2 output.

“The results show, without question, that the gap between lab and real-world PHEV energy use and CO₂ output is much, much larger than for petrol or conventional vehicles,” the expert stated. “Any regulatory adjustments regarding PHEVs should be made with utmost care and considering that data.”