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Plug-in hybrid electric vehicles release nearly five times greater global warming pollution than official data show, according to a new analysis.

Widening Gap Between Official and Actual Emissions

Data reveals that PHEVs emit only 19% less CO₂ than conventional petrol and diesel vehicles, based on analysis carried out by a non-profit group. This contrasts significantly with lab tests, which assumed a three-quarters decrease in emissions.

Researchers examined information from onboard fuel consumption meters of eight hundred thousand vehicles sold in the EU from 2021 and 2023. They found that actual CO₂ output from PHEVs in 2023 were 4.9 times greater than lab figures, up from three and a half times in 2021.

“Actual emissions are rising, while official emissions are falling,” said a senior analyst involved in the report. “This gap is growing and poses a significant issue. Consequently, PHEVs emit nearly as much as gasoline vehicles.”

Primary Reasons Behind the Emissions Gap

Researchers attributed most of the difference to overestimates of the “utility factor” – the percentage of miles travelled in electric mode relative to total mileage. They determined that only 27% of driving was completed in electric mode, whereas lab assumptions suggested 84%.

Additionally, when operating in EV mode, emission levels were well above official estimates. That happened because electric motors were insufficiently powerful sufficient to function independently, resulting to engines using fossil fuels for almost one-third of the distance covered in electric mode.

Policy and Economic Implications

Based on calculations, the underestimation of PHEV emissions enabled four large automaker groups to escape more than €5bn in fines between 2021 and 2023, by artificially easing compliance with European Union fleet-average CO₂ targets.

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

“The strong claims that manufacturers like to make about their plug-in hybrid cars are obviously far from the mark,” stated a transport analyst. “Buyers are being misled into thinking that by purchasing a PHEV, they are benefiting the planet and cutting money. In reality, PHEVs are only slightly improved than regular petrol and diesel vehicles in terms of energy consumption, CO₂ emissions, and running costs.”

Political Discussion and Industry Pressure

Plug-in hybrid cars have lately been drawn back into political discussions as carmakers have lobbied the EU to weaken CO₂ standards. A proposed ban on sales of new combustion engine vehicles in 2035 has faced intense lobbying from the automotive sector and resistance from member states with large automotive manufacturing.

Several senior officials have suggested PHEVs as a potential “compromise” option to introduce in the legislation.

An independent energy economics expert, who was not involved with the study, called the report a “highly valuable addition” after years in which parts of the car industry argued there was too little information to properly evaluate actual emissions.

“These findings show, beyond any doubt, that the gap in lab and actual PHEV energy use and CO₂ emissions is much, much larger than for gasoline or conventional vehicles,” they stated. “Any regulatory adjustments regarding PHEVs should be implemented with extreme caution and considering that data.”