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Plug-in hybrid cars produce nearly 5x more planet-heating pollution than official data show, according to a new report.

Growing Gap In Official and Real-World CO2 Output

Statistics reveals that PHEVs emit only 19% lower CO₂ than traditional petrol and diesel cars, based on analysis conducted by a non-profit group. This contrasts significantly with lab estimates, which assumed a 75% reduction in pollution.

Researchers examined data from onboard energy use meters of 800,000 cars registered in Europe between 2021 and 2023. The team discovered that actual CO₂ output from PHEVs in 2023 were nearly five times greater than lab figures, up from three and a half times in 2021.

“Real-world CO2 output are rising, while lab-reported emissions are decreasing,” stated a senior researcher participating in the report. “This discrepancy is growing and poses a serious issue. As a result, PHEVs pollute nearly as much as petrol cars.”

Key Factors Behind the Emissions Gap

Researchers attributed the majority of the gap to inflated estimates of the “electric driving share” – the percentage of kilometers driven in battery power relative to overall mileage. They found that only a quarter of driving was done in electric mode, while lab estimates assumed over four-fifths.

Additionally, when running in electric mode, emission levels were significantly higher than official estimates. That happened because electric motors were not strong sufficient to operate independently, resulting to engines burning gasoline for almost a third of the distance completed in EV mode.

Policy and Economic Implications

According to estimates, the underestimation of PHEV CO2 output allowed several large automaker companies to avoid over €5bn in penalties between 2021 and 2023, by falsely easing compliance with European Union average fleet CO₂ standards.

Additionally, drivers of PHEVs could spend approximately €500 extra per year in running expenses than would be estimated under laboratory tests.

“The bold statements that manufacturers like to make about their PHEV vehicles are obviously way off the truth,” stated a transport expert. “Buyers are being duped into believing that by buying a PHEV, they are benefiting the environment and cutting money. In reality, PHEVs are little improved than regular petrol and diesel vehicles in terms of fuel use, CO₂ production, and running costs.”

Political Debate and Industry Pressure

Hybrid vehicles have recently been brought again into policy discussions as automakers have pressed the European Union to weaken CO₂ standards. A planned prohibition on sales of new combustion engine vehicles in 2035 has faced heavy pressure from the automotive industry and resistance from EU countries with significant automotive industries.

Several senior politicians have suggested PHEVs as a potential “compromise” solution to include in the legislation.

One external energy policy specialist, who was unaffiliated with the research, called the report a “highly valuable addition” after years in which segments of the automotive industry argued there was too little information to properly assess real-world CO2 output.

“These findings demonstrate, without question, that the difference between official and actual PHEV fuel consumption and CO₂ output is much, much greater than for gasoline or conventional cars,” the expert stated. “Any policy adjustments regarding PHEVs should be implemented with utmost caution and considering that data.”