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Plug-in hybrid cars release almost five times greater planet-heating emissions than official data show, according to a recent analysis.

Widening Discrepancy Between Lab and Real-World CO2 Output

Statistics reveals that PHEVs emit just 19% lower CO₂ than conventional petrol and diesel cars, according to analysis conducted by a advocacy group. This differs significantly with lab estimates, which suggested a 75% reduction in emissions.

Analysts studied data from onboard energy use monitors of eight hundred thousand cars registered in the EU from 2021 and 2023. The team found that real-world CO₂ output from PHEVs in 2023 were 4.9 times higher than lab estimates, up from three and a half times in 2021.

“Real-world CO2 output are rising, while lab-reported figures are falling,” said a lead researcher involved in the study. “That discrepancy is widening and creates a serious issue. Consequently, PHEVs pollute almost as heavily as petrol cars.”

Key Factors Behind the Discrepancy

Researchers linked the majority of the gap to inflated estimates of the “electric driving share” – the percentage of kilometers travelled in battery mode compared to total distance. They found that just 27% of travel was completed in electric mode, whereas lab estimates assumed over four-fifths.

Additionally, when operating in electric mode, pollution levels were well above official estimates. That happened because electric motors were insufficiently powerful enough to function independently, leading to engines burning gasoline for nearly one-third of the distance covered in EV mode.

Regulatory and Financial Implications

Based on calculations, the underestimation of PHEV CO2 output enabled four large carmaker companies to escape more than €5bn in fines from 2021 and 2023, by artificially simplifying adherence with EU fleet-average CO₂ standards.

Additionally, owners of PHEVs would pay about €500 extra annually in operating costs than is estimated under lab conditions.

“The strong claims that manufacturers like to make about their PHEV vehicles are clearly way off the mark,” commented a automotive expert. “Buyers are being misled into believing that by purchasing a PHEV, they are benefiting the environment and saving costs. In reality, PHEVs are only slightly better than standard gas and diesel cars in terms of energy consumption, CO₂ production, and operating expenses.”

Political Discussion and Industry Pressure

Hybrid vehicles have recently been brought back into policy debates as carmakers have lobbied the EU to weaken CO₂ standards. A proposed ban on sales of new combustion engine cars in 2035 has faced heavy pressure from the car industry and resistance from member states with large automotive manufacturing.

Several high-level officials have suggested PHEVs as a potential “flexibility” option to introduce in the regulation.

One independent energy policy expert, who was unaffiliated with the study, called the analysis a “very useful contribution” after a long period in which parts of the car industry claimed there was too little data to accurately evaluate real-world CO2 output.

“These findings show, beyond any doubt, that the difference in official and real-world PHEV energy use and CO₂ output is significantly greater than for gasoline or conventional cars,” they stated. “All policy changes regarding PHEVs should be implemented with extreme caution and in the light of this data.”