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Plug-in hybrid electric vehicles emit almost five times greater global warming emissions than lab-reported data indicate, according to a new report.

Growing Gap Between Lab and Actual Emissions

Data shows that PHEVs release only one-fifth lower CO₂ than traditional gas and diesel vehicles, according to analysis conducted by a non-profit group. That differs significantly with lab estimates, which assumed a 75% decrease in emissions.

Researchers studied information from onboard energy use meters of 800,000 cars registered in the EU from 2021 and 2023. The team discovered that real-world CO₂ output from PHEVs in 2023 were nearly five times higher than official estimates, increased from 3.5 times in 2021.

“Real-world CO2 output are rising, while lab-reported figures are decreasing,” said a lead researcher participating in the study. “This discrepancy is widening and poses a serious issue. Consequently, PHEVs emit almost as much as petrol cars.”

Primary Reasons Driving the Emissions Gap

Researchers attributed the majority of the difference to overestimates of the “electric driving share” – the percentage of kilometers travelled in electric mode compared to overall distance. The team found that only a quarter of driving was completed in electric mode, while official estimates suggested 84%.

Additionally, when operating in electric mode, pollution levels were significantly higher than official estimates. This occurred because EV motors were not strong sufficient to operate alone, leading to combustion motors burning gasoline for almost a third of the travel covered in EV mode.

Regulatory and Financial Implications

Based on calculations, the lowballing of PHEV CO2 output enabled several large carmaker groups to avoid more than €5bn in penalties from 2021 and 2023, by falsely simplifying adherence with European Union fleet-average CO₂ standards.

Additionally, owners of PHEVs would spend about €500 extra per year in running expenses than is assumed under laboratory conditions.

“The strong claims that manufacturers like to make about their PHEV cars are obviously way off the truth,” stated a automotive analyst. “Consumers are being duped into thinking that by buying a PHEV, they are benefiting the environment and saving money. Actually, PHEVs are only slightly improved than standard gas and diesel cars in terms of energy consumption, CO₂ emissions, and operating costs.”

Policy Discussion and Industry Lobbying

Plug-in hybrid cars have lately been brought again into policy discussions as automakers have lobbied the European Union to weaken CO₂ targets. A planned prohibition on new combustion engine vehicles in 2035 has faced heavy lobbying from the automotive industry and opposition from member states with significant automotive manufacturing.

Some high-level politicians have suggested plug-in hybrids as a possible “flexibility” option to introduce in the legislation.

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

“The results demonstrate, beyond any doubt, that the difference in lab and real-world PHEV energy use and CO₂ output is much, much larger than for petrol or conventional vehicles,” the expert said. “Any regulatory adjustments concerning PHEVs should be implemented with utmost care and considering that data.”