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Plug-in hybrid cars release nearly 5x more global warming emissions than lab-reported data indicate, as per a recent analysis.

Growing Discrepancy Between Official and Real-World Emissions

Data shows that PHEVs emit just 19% lower CO₂ than conventional gas and diesel vehicles, based on analysis carried out by a non-profit group. That contrasts sharply with laboratory estimates, which suggested a three-quarters reduction in pollution.

Researchers studied information from in-vehicle fuel consumption monitors of 800,000 vehicles registered in the EU between 2021 and 2023. The team found that actual CO₂ output from PHEVs in 2023 were 4.9 times greater than lab figures, increased from 3.5 times in 2021.

“Actual CO2 output are rising, while official figures are decreasing,” said a senior analyst participating in the study. “That gap is growing and creates a serious issue. As a result, PHEVs emit almost as heavily as petrol cars.”

Key Reasons Driving the Discrepancy

Analysts attributed most of the gap to overestimates of the “electric driving share” – the percentage of kilometers travelled in electric mode compared to total distance. They found that just 27% of travel was completed in EV mode, while lab estimates suggested over four-fifths.

Additionally, when operating in EV mode, emission amounts were well above lab projections. That occurred because EV motors were not strong enough to operate independently, leading to combustion motors burning gasoline for nearly one-third of the travel completed in EV mode.

Regulatory and Economic Implications

Based on estimates, the lowballing of PHEV CO2 output allowed several large carmaker groups to avoid over €5bn in fines from 2021 and 2023, by artificially simplifying compliance with European Union fleet-average CO₂ targets.

Furthermore, owners of PHEVs could spend about €500 more annually in operating costs than is estimated under lab conditions.

“The bold claims that automakers often promote about their PHEV cars are clearly far from the truth,” stated a transport expert. “Consumers are being misled into believing that by purchasing a PHEV, they are helping the environment and saving costs. Actually, PHEVs are little improved than regular gas and diesel cars in terms of energy consumption, CO₂ production, and operating costs.”

Policy Discussion and Automotive Pressure

Plug-in hybrid vehicles have lately been brought again into policy discussions as automakers have lobbied the EU to relax CO₂ standards. A planned ban on new combustion engine cars in 2035 has faced intense pressure from the car sector and opposition from member states with significant automotive manufacturing.

Several high-level politicians have proposed PHEVs as a possible “compromise” solution to include in the regulation.

One external energy policy expert, who was unaffiliated with the study, called the report a “very useful contribution” after years in which segments of the automotive industry argued there was too little information to accurately assess real-world emissions.

“The results show, beyond any doubt, that the difference between official and actual PHEV fuel consumption and CO₂ output is much, much larger than for petrol or diesel cars,” the expert stated. “All regulatory adjustments concerning PHEVs should be made with utmost care and in the light of this evidence.”