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Plug-in hybrid cars produce nearly 5x more planet-heating emissions than lab-reported data indicate, according to a new analysis.

Widening Discrepancy Between Lab and Actual CO2 Output

Data reveals that PHEVs emit only one-fifth lower CO₂ than traditional gas and diesel cars, according to analysis conducted by a non-profit organization. This differs significantly with lab estimates, which suggested a three-quarters reduction in emissions.

Researchers examined information from onboard fuel consumption meters of 800,000 cars sold in Europe from 2021 and 2023. The team found that real-world CO₂ output from PHEVs in 2023 were nearly five times higher than lab figures, increased from 3.5 times in 2021.

“Real-world emissions are increasing, while lab-reported emissions are falling,” stated a lead analyst participating in the report. “This discrepancy is growing and creates a significant issue. Consequently, PHEVs emit nearly as much as gasoline cars.”

Key Factors Driving the Discrepancy

Analysts attributed the majority of the difference to overestimates of the “electric driving share” – the percentage of miles driven in electric power compared to overall distance. They found that only 27% of driving was done in EV mode, while lab assumptions suggested 84%.

Additionally, when running in EV mode, emission levels were significantly higher than lab estimates. That happened because EV motors were not strong enough to operate alone, leading to combustion motors burning fossil fuels for nearly a third of the travel covered in electric mode.

Policy and Financial Consequences

According to estimates, the underestimation of PHEV emissions enabled four major automaker groups to escape over €5bn in penalties between 2021 and 2023, by artificially easing adherence with EU average fleet CO₂ standards.

Furthermore, owners of PHEVs would pay about €500 more per year in operating expenses than would be assumed under laboratory conditions.

“The strong claims that manufacturers often promote about their PHEV cars are obviously far from the mark,” commented a automotive expert. “Consumers are being duped into believing that by purchasing a PHEV, they are helping the environment and cutting money. In reality, PHEVs are little better than regular gas and diesel vehicles in terms of energy consumption, CO₂ production, and running costs.”

Political Discussion and Industry Lobbying

Plug-in hybrid cars have recently been drawn again into policy debates as automakers have pressed the European Union to relax CO₂ standards. A proposed prohibition on sales of new combustion engine vehicles in 2035 has faced intense lobbying from the car industry and resistance from EU countries with large car manufacturing.

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

An external energy economics expert, who was unaffiliated with the study, described the report a “very useful contribution” after a long period in which segments of the automotive sector claimed there was too little data to accurately assess real-world CO2 output.

“These findings show, beyond any doubt, that the gap in official and real-world PHEV energy use and CO₂ output is significantly larger than for petrol or conventional cars,” they said. “Any policy changes concerning PHEVs should be implemented with utmost care and in the light of that evidence.”