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Plug-in hybrid electric vehicles release nearly five times greater global warming emissions than lab-reported data show, according to a new report.

Widening Discrepancy In Official and Actual CO2 Output

Data reveals that PHEVs release only one-fifth less CO₂ than conventional petrol and diesel vehicles, based on research conducted by a advocacy organization. That contrasts significantly with laboratory estimates, which suggested a 75% reduction in pollution.

Analysts examined information from in-vehicle energy use monitors of 800,000 cars registered in Europe between 2021 and 2023. They discovered that real-world CO₂ emissions from PHEVs in 2023 were nearly five times greater than lab estimates, up from 3.5 times in 2021.

“Real-world CO2 output are increasing, while official emissions are decreasing,” stated a lead analyst involved in the report. “That gap is growing and poses a significant issue. Consequently, PHEVs emit nearly as heavily as petrol cars.”

Primary Factors Behind the Discrepancy

Researchers linked the majority of the difference to overestimates of the “utility factor” – the percentage of miles driven in battery power relative to overall distance. The team found that just a quarter of travel was completed in EV mode, whereas lab assumptions assumed over four-fifths.

Additionally, when running in electric mode, emission levels were significantly higher than official projections. That occurred because EV motors were not strong sufficient to operate independently, leading to engines burning gasoline for nearly a third of the travel covered in EV mode.

Policy and Financial Implications

According to calculations, the underestimation of PHEV CO2 output enabled several large automaker groups to avoid more than €5bn in penalties between 2021 and 2023, by falsely simplifying compliance with EU average fleet CO₂ standards.

Furthermore, owners of PHEVs would spend about €500 more per year in running expenses than is estimated under lab tests.

“The bold claims that automakers like to make about their PHEV vehicles are obviously way off the truth,” commented a transport analyst. “Buyers are being duped into believing that by buying a PHEV, they are helping the environment and cutting money. Actually, PHEVs are only slightly better than standard petrol and diesel cars in terms of energy consumption, CO₂ production, and running costs.”

Policy Discussion and Automotive Lobbying

Hybrid cars have recently been drawn again into political debates as carmakers have lobbied the European Union to weaken CO₂ standards. A proposed prohibition on sales of new combustion engine vehicles in 2035 has faced intense lobbying from the car industry and opposition from member states with large car manufacturing.

Several high-level politicians have proposed plug-in hybrids as a potential “compromise” solution to include in the legislation.

An external energy policy expert, who was unaffiliated with the study, called the report a “highly valuable contribution” after a long period in which parts of the automotive sector argued there was too little data to accurately evaluate actual emissions.

“These findings show, without question, that the difference in lab and actual PHEV energy use and CO₂ output is significantly larger than for gasoline or conventional cars,” they stated. “All regulatory adjustments regarding PHEVs should be implemented with extreme caution and in the light of this data.”