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Plug-in hybrid electric vehicles release nearly 5x more planet-heating emissions than lab-reported figures show, according to a new report.

Growing Discrepancy In Official and Real-World CO2 Output

Statistics shows that PHEVs release only one-fifth less CO₂ than conventional petrol and diesel vehicles, based on research carried out by a advocacy organization. That contrasts significantly with lab estimates, which assumed a three-quarters reduction in emissions.

Researchers studied information from in-vehicle fuel consumption meters of 800,000 vehicles sold in Europe between 2021 and 2023. The team found that actual CO₂ output from PHEVs in 2023 were 4.9 times greater than official figures, up from 3.5 times in 2021.

“Actual CO2 output are rising, while lab-reported emissions are decreasing,” said a senior researcher participating in the report. “That discrepancy is widening and poses a significant problem. Consequently, PHEVs pollute nearly as heavily as gasoline vehicles.”

Primary Factors Behind the Discrepancy

Analysts linked most of the gap to overestimates of the “electric driving share” – the percentage of miles driven in electric mode relative to overall distance. The team determined that just 27% of driving was completed in EV mode, whereas lab assumptions assumed over four-fifths.

Even, when running in electric mode, pollution amounts were significantly higher than official estimates. This happened because EV motors were not strong sufficient to operate alone, leading to engines using fossil fuels for nearly a third of the travel completed in electric mode.

Policy and Financial Implications

Based on calculations, the underestimation of PHEV CO2 output enabled several major carmaker companies to escape more than €5bn in fines between 2021 and 2023, by artificially simplifying adherence with EU average fleet CO₂ targets.

Furthermore, owners of PHEVs would spend about €500 extra per year in operating expenses than is estimated under lab conditions.

“The strong claims that manufacturers often promote about their PHEV vehicles are obviously far from the truth,” stated a transport expert. “Consumers are being duped into believing that by purchasing a PHEV, they are helping the environment and saving costs. In reality, PHEVs are only slightly better than regular petrol and diesel vehicles in terms of energy consumption, CO₂ production, and running costs.”

Political Discussion and Automotive Pressure

Hybrid vehicles have recently been drawn again into political discussions as automakers have lobbied the EU to relax CO₂ standards. A planned ban on new combustion engine cars in 2035 has faced intense lobbying from the automotive sector and opposition from EU countries with significant car industries.

Some high-level officials have suggested plug-in hybrids as a possible “compromise” solution to include in the legislation.

One external energy policy specialist, who was not involved with the study, described the analysis a “highly valuable contribution” after a long period in which segments of the car sector argued there was too little data to properly evaluate real-world CO2 output.

“The results show, without question, that the gap in lab and real-world PHEV fuel consumption and CO₂ output is much, much greater than for gasoline or conventional cars,” the expert stated. “Any regulatory adjustments regarding PHEVs should be implemented with extreme caution and in the light of this data.”