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Plug-in hybrid cars emit almost 5x greater global warming emissions than official data indicate, according to a new analysis.

Widening Discrepancy Between Lab and Real-World CO2 Output

Data shows that PHEVs emit only 19% less CO₂ than traditional petrol and diesel cars, according to research conducted by a advocacy organization. This contrasts sharply with laboratory estimates, which assumed a three-quarters reduction in emissions.

Analysts examined information from onboard energy use monitors of eight hundred thousand vehicles registered in Europe from 2021 and 2023. The team found that actual CO₂ output from PHEVs in 2023 were 4.9 times greater than official estimates, increased from 3.5 times in 2021.

“Actual CO2 output are rising, while official figures are falling,” stated a senior researcher participating in the study. “This discrepancy is growing and creates a significant problem. Consequently, PHEVs emit nearly as heavily as petrol cars.”

Key Reasons Driving the Discrepancy

Analysts attributed most of the difference to overestimates of the “electric driving share” – the ratio of miles driven in electric power relative to total distance. The team found that only a quarter of driving was done in EV mode, whereas official assumptions assumed 84%.

Even, when running in electric mode, emission amounts were significantly higher than official projections. That occurred because electric motors were not strong sufficient to function independently, resulting to combustion motors burning gasoline for almost one-third of the distance covered in electric mode.

Policy and Financial Implications

Based on calculations, the underestimation of PHEV CO2 output allowed several large carmaker companies to escape more than €5bn in fines between 2021 and 2023, by falsely easing compliance with EU fleet-average CO₂ targets.

Additionally, drivers of PHEVs would pay approximately €500 more annually in operating costs than is assumed under laboratory conditions.

“The strong statements that automakers like to make about their PHEV cars are clearly way off the truth,” stated a transport expert. “Buyers are being duped into believing that by buying a PHEV, they are benefiting the planet and saving money. In reality, PHEVs are only slightly improved than regular petrol and diesel vehicles in terms of fuel use, CO₂ emissions, and running expenses.”

Policy Discussion and Automotive Pressure

Plug-in hybrid cars have lately been brought back into political debates as carmakers have pressed the European Union to weaken CO₂ standards. A planned prohibition on new internal combustion vehicles in 2035 has faced intense lobbying from the automotive industry and opposition from member states with large automotive industries.

Several senior officials have suggested plug-in hybrids as a possible “compromise” option to introduce in the legislation.

An independent energy economics specialist, who was not involved with the study, described the report a “very useful addition” after a long period in which segments of the automotive sector claimed there was insufficient data to accurately evaluate real-world CO2 output.

“These findings demonstrate, beyond any doubt, that the difference between lab and real-world PHEV energy use and CO₂ emissions is much, much larger than for petrol or diesel cars,” they said. “All regulatory changes regarding PHEVs should be implemented with utmost care and in the light of that data.”