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Plug-in hybrid electric vehicles release almost 5x greater global warming emissions than lab-reported figures indicate, according to a new analysis.

Growing Gap In Lab and Real-World Emissions

Data shows that PHEVs release just 19% lower CO₂ than traditional petrol and diesel cars, based on analysis conducted by a advocacy group. That contrasts significantly with lab estimates, which suggested a 75% decrease in pollution.

Researchers studied information from onboard fuel consumption meters of 800,000 vehicles sold in the EU from 2021 and 2023. They found that real-world CO₂ output from PHEVs in 2023 were nearly five times greater than lab estimates, increased from 3.5 times in 2021.

“Real-world CO2 output are increasing, while official emissions are falling,” said a lead analyst involved in the report. “This discrepancy is widening and poses a serious problem. Consequently, PHEVs pollute nearly as heavily as petrol cars.”

Primary Factors Driving the Emissions Gap

Researchers linked most of the difference to overestimates of the “electric driving share” – the percentage of kilometers driven in electric mode relative to overall distance. The team found that only a quarter of travel was done in electric mode, while official assumptions suggested 84%.

Even, when operating in electric mode, pollution amounts were significantly higher than lab projections. This happened because EV motors were not strong sufficient to operate independently, leading to combustion motors burning fossil fuels for almost a third of the travel completed in EV mode.

Policy and Financial Implications

According to calculations, the lowballing of PHEV CO2 output allowed four large carmaker companies to avoid over €5bn in fines from 2021 and 2023, by artificially easing compliance with EU average fleet CO₂ targets.

Additionally, owners of PHEVs would spend about €500 more per year in operating expenses than is assumed under lab conditions.

“The strong statements that automakers like to make about their plug-in hybrid cars are obviously far from the mark,” commented a transport analyst. “Consumers are being duped into believing that by buying a PHEV, they are helping the planet and saving costs. Actually, PHEVs are little better than standard gas and diesel cars in terms of fuel consumption, CO₂ production, and operating costs.”

Political Discussion and Industry Pressure

Hybrid cars have recently been brought again into political discussions as carmakers have lobbied the EU to weaken CO₂ standards. A planned ban on new internal combustion vehicles in 2035 has faced intense lobbying from the car sector and opposition from EU countries with significant car manufacturing.

Several high-level politicians have suggested plug-in hybrids as a potential “flexibility” solution to include in the regulation.

An external energy economics expert, who was not involved with the study, described the analysis a “very useful addition” after years in which parts of the automotive sector claimed there was too little information to accurately evaluate real-world CO2 output.

“The results demonstrate, without question, that the gap between official and real-world PHEV energy use and CO₂ output is much, much larger than for petrol or diesel vehicles,” the expert said. “Any regulatory adjustments regarding PHEVs should be implemented with extreme caution and considering that evidence.”