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Plug-in hybrid electric vehicles release nearly 5x greater global warming pollution than lab-reported data show, as per a recent report.

Widening Gap In Lab and Actual Emissions

Data shows that PHEVs release only 19% lower CO₂ than conventional gas and diesel vehicles, based on research conducted by a non-profit group. This contrasts sharply with laboratory estimates, which suggested a three-quarters reduction in pollution.

Researchers studied information from onboard fuel consumption monitors of 800,000 cars sold in the EU between 2021 and 2023. They found that actual CO₂ output from PHEVs in 2023 were 4.9 times greater than lab estimates, up from 3.5 times in 2021.

“Actual CO2 output are increasing, while official emissions are decreasing,” said a senior researcher involved in the study. “This discrepancy is growing and poses a significant problem. As a result, PHEVs pollute nearly as heavily as petrol cars.”

Primary Reasons Driving the Emissions Gap

Researchers attributed most of the difference to overestimates of the “utility factor” – the percentage of miles driven in electric power compared to total mileage. The team determined that just a quarter of travel was completed in EV mode, while official assumptions assumed over four-fifths.

Additionally, when operating in EV mode, pollution levels were significantly higher than lab projections. That happened because EV motors were insufficiently powerful enough to operate alone, leading to engines using fossil fuels for nearly one-third of the distance covered in EV mode.

Regulatory and Financial Consequences

According to calculations, the underestimation of PHEV CO2 output allowed four major carmaker companies to avoid over €5bn in fines from 2021 and 2023, by falsely simplifying adherence with EU fleet-average CO₂ targets.

Additionally, owners of PHEVs would pay approximately €500 extra per year in operating costs than would be assumed under laboratory tests.

“The strong statements that manufacturers like to make about their PHEV vehicles are obviously way off the mark,” commented a transport analyst. “Buyers are being misled into believing that by purchasing a PHEV, they are benefiting the environment and cutting costs. Actually, PHEVs are only slightly better than standard gas and diesel cars in terms of energy consumption, CO₂ emissions, and operating costs.”

Political Discussion and Industry Pressure

Plug-in hybrid vehicles have lately been brought back into policy debates as carmakers have pressed the European Union to weaken CO₂ standards. A proposed ban on sales of new combustion engine vehicles in 2035 has faced intense pressure from the automotive sector and opposition from member states with large car manufacturing.

Several senior politicians have proposed PHEVs as a potential “compromise” option to introduce in the regulation.

One independent energy policy expert, who was unaffiliated with the study, described the analysis a “highly valuable addition” after a long period in which segments of the car industry argued there was insufficient data to accurately assess real-world emissions.

“The results demonstrate, without question, that the gap between official and real-world PHEV energy use and CO₂ output is much, much greater than for petrol or diesel vehicles,” the expert stated. “Any regulatory adjustments regarding PHEVs should be made with extreme care and in the light of that data.”