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Plug-in hybrid electric vehicles release nearly 5x more global warming pollution than official figures show, according to a new analysis.

Growing Discrepancy In Lab and Real-World Emissions

Data shows that PHEVs release only 19% lower CO₂ than conventional petrol and diesel cars, based on analysis conducted by a non-profit group. That differs significantly with lab tests, which suggested a 75% reduction in emissions.

Analysts studied information from in-vehicle fuel consumption monitors of eight hundred thousand cars sold in the EU from 2021 and 2023. They found that real-world CO₂ emissions from PHEVs in 2023 were 4.9 times greater than official estimates, increased from 3.5 times in 2021.

“Real-world emissions are increasing, while official emissions are falling,” said a lead researcher involved in the study. “This gap is growing and poses a serious issue. Consequently, PHEVs emit nearly as heavily as gasoline cars.”

Key Factors Behind the Discrepancy

Analysts linked most of the gap to inflated estimates of the “utility factor” – the percentage of miles driven in electric power compared to total mileage. The team found that just a quarter of travel was done in electric mode, while official estimates assumed over four-fifths.

Additionally, when running in EV mode, pollution amounts were well above official projections. This occurred because EV motors were not strong enough to function independently, resulting to engines burning gasoline for nearly one-third of the travel completed in EV mode.

Policy and Economic Implications

Based on estimates, the underestimation of PHEV emissions enabled four large automaker companies to escape over €5bn in penalties between 2021 and 2023, by artificially easing compliance with European Union average fleet CO₂ targets.

Furthermore, owners of PHEVs would spend about €500 extra per year in running costs than would be assumed under lab conditions.

“The strong claims that automakers like to make about their PHEV vehicles are obviously far from the mark,” commented a transport analyst. “Buyers are being misled into believing that by purchasing a PHEV, they are helping the planet and saving costs. In reality, PHEVs are little improved than regular gas and diesel cars in terms of energy use, CO₂ emissions, and operating costs.”

Policy Debate and Industry Lobbying

Plug-in hybrid cars have lately been brought back into policy debates as carmakers have lobbied the European Union to relax CO₂ targets. A proposed ban on new combustion engine vehicles in 2035 has faced intense lobbying from the car industry and opposition from member states with large car manufacturing.

Some senior officials have proposed plug-in hybrids as a potential “compromise” option to include in the legislation.

One independent energy economics expert, who was not involved with the study, called the report a “very useful contribution” after a long period in which parts of the automotive sector argued there was insufficient data to properly evaluate real-world CO2 output.

“The results demonstrate, beyond any doubt, that the gap between lab and real-world PHEV energy use and CO₂ emissions is much, much greater than for petrol or diesel cars,” the expert stated. “All policy changes concerning PHEVs should be implemented with utmost caution and in the light of this evidence.”