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Plug-in hybrid electric vehicles release almost 5x greater global warming pollution than lab-reported data show, according to a new analysis.

Widening Gap Between Lab and Actual CO2 Output

Data reveals that PHEVs release just 19% less CO₂ than conventional petrol and diesel vehicles, based on analysis carried out by a advocacy organization. This differs significantly with laboratory estimates, which suggested a 75% decrease in pollution.

Analysts examined data from onboard energy use meters of 800,000 cars registered in the EU from 2021 and 2023. They found that actual CO₂ output from PHEVs in 2023 were 4.9 times higher than lab figures, increased from 3.5 times in 2021.

“Real-world emissions are increasing, while lab-reported figures are falling,” said a lead researcher participating in the report. “That discrepancy is growing and creates a significant problem. Consequently, PHEVs emit almost as much as petrol vehicles.”

Key Factors Behind the Emissions Gap

Analysts attributed the majority of the difference to overestimates of the “utility factor” – the percentage of kilometers travelled in battery mode compared to total distance. The team found that just 27% of driving was completed in electric mode, whereas official estimates assumed 84%.

Even, when operating in electric mode, pollution levels were well above official estimates. That occurred because electric motors were not strong sufficient to function independently, leading to combustion motors burning gasoline for nearly one-third of the distance completed in electric mode.

Policy and Financial Consequences

According to estimates, the lowballing of PHEV emissions allowed four major automaker companies to escape more than €5bn in penalties between 2021 and 2023, by artificially simplifying adherence with European Union average fleet CO₂ standards.

Additionally, owners of PHEVs would spend about €500 more annually in running expenses than would be assumed under lab conditions.

“The bold statements that automakers often promote about their plug-in hybrid vehicles are obviously way off the mark,” commented a transport analyst. “Consumers are being misled into believing that by buying a PHEV, they are helping the environment and saving costs. In reality, PHEVs are only slightly better than standard gas and diesel vehicles in terms of fuel use, CO₂ production, and operating expenses.”

Policy Discussion and Industry Pressure

Hybrid cars have recently been drawn back into political debates as carmakers have lobbied the EU to relax CO₂ standards. A proposed prohibition on new combustion engine vehicles in 2035 has faced intense pressure from the automotive industry and resistance from EU countries with large car manufacturing.

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

One external energy policy expert, who was not involved with the research, called the report a “very useful addition” after years in which segments of the car sector argued there was too little data to properly assess real-world CO2 output.

“These findings demonstrate, without question, that the difference in lab and real-world PHEV energy use and CO₂ output is significantly larger than for gasoline or diesel vehicles,” they stated. “Any regulatory adjustments regarding PHEVs should be made with extreme caution and in the light of that data.”