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Plug-in hybrid cars produce almost five times greater planet-heating pollution than official figures indicate, according to a new analysis.

Widening Discrepancy Between Lab and Actual Emissions

Data reveals that PHEVs emit just one-fifth less CO₂ than conventional petrol and diesel cars, based on research carried out by a advocacy group. This contrasts significantly with lab estimates, which assumed a three-quarters reduction in pollution.

Analysts studied information from onboard energy use monitors of eight hundred thousand cars registered in Europe from 2021 and 2023. They found that actual CO₂ emissions from PHEVs in 2023 were nearly five times higher than lab figures, up from three and a half times in 2021.

“Actual emissions are rising, while official figures are decreasing,” said a lead analyst participating in the study. “This gap is widening and creates a serious problem. Consequently, PHEVs pollute almost as heavily as petrol vehicles.”

Key Factors Driving the Discrepancy

Analysts linked most of the gap to inflated estimates of the “electric driving share” – the ratio of miles driven in battery mode compared to total mileage. They found that only a quarter of travel was completed in EV mode, while official estimates suggested 84%.

Additionally, when running in electric mode, pollution amounts were significantly higher than official estimates. That happened because EV motors were not strong enough to function alone, resulting to combustion motors burning fossil fuels for nearly one-third of the distance completed in EV mode.

Regulatory and Economic Consequences

According to calculations, the underestimation of PHEV CO2 output allowed several large carmaker companies to escape more than €5bn in fines between 2021 and 2023, by artificially easing compliance with European Union average fleet CO₂ targets.

Additionally, drivers of PHEVs could spend about €500 extra annually in running expenses than is estimated under laboratory tests.

“The bold statements that manufacturers often promote about their plug-in hybrid cars are clearly far from the truth,” stated a transport expert. “Consumers are being misled into believing that by purchasing a PHEV, they are helping the planet and cutting costs. In reality, PHEVs are only slightly better than standard gas and diesel vehicles in terms of fuel use, CO₂ production, and running costs.”

Policy Discussion and Automotive Pressure

Hybrid vehicles have lately been drawn again into policy discussions as automakers have lobbied the European Union to weaken CO₂ standards. A proposed prohibition on new combustion engine cars in 2035 has faced intense pressure from the car sector and resistance from EU countries with large automotive industries.

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

One external energy economics specialist, who was not involved with the research, described the analysis a “very useful addition” after years in which parts of the automotive industry claimed there was insufficient information to accurately evaluate actual CO2 output.

“The results show, without question, that the gap in official and real-world PHEV energy use and CO₂ output is much, much greater than for gasoline or conventional cars,” they said. “Any policy adjustments concerning PHEVs should be made with extreme caution and in the light of this data.”