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Plug-in hybrid cars emit nearly 5x more planet-heating pollution than lab-reported data show, according to a new analysis.

Widening Discrepancy In Official and Actual CO2 Output

Data reveals that PHEVs emit only one-fifth less CO₂ than conventional petrol and diesel vehicles, based on research conducted by a advocacy group. That contrasts sharply with laboratory estimates, which assumed a three-quarters reduction in emissions.

Researchers studied information from in-vehicle energy use monitors of eight hundred thousand cars sold in the EU from 2021 and 2023. They discovered that real-world CO₂ emissions from PHEVs in 2023 were nearly five times greater than lab figures, up from 3.5 times in 2021.

“Real-world CO2 output are increasing, while official emissions are falling,” said a lead researcher involved in the study. “This discrepancy is widening and poses a significant issue. As a result, PHEVs pollute nearly as much as petrol cars.”

Key Factors Behind the Emissions Gap

Analysts attributed the majority of the difference to inflated estimates of the “utility factor” – the ratio of kilometers travelled in battery mode compared to overall mileage. The team determined that just 27% of travel was completed in EV mode, while official estimates suggested over four-fifths.

Additionally, when running in EV mode, pollution levels were significantly higher than official estimates. That occurred because EV motors were not strong enough to function alone, leading to combustion motors using fossil fuels for almost a third of the distance completed in EV mode.

Regulatory and Financial Consequences

Based on estimates, the underestimation of PHEV emissions allowed several major carmaker companies to avoid more than €5bn in fines between 2021 and 2023, by artificially simplifying adherence with European Union average fleet CO₂ standards.

Furthermore, owners of PHEVs could pay about €500 extra annually in operating costs than is assumed under lab tests.

“The bold statements that manufacturers often promote about their PHEV cars are clearly way off the truth,” stated a transport analyst. “Buyers are being misled into believing that by purchasing a PHEV, they are benefiting the planet and saving costs. In reality, PHEVs are only slightly improved than regular petrol and diesel cars in terms of fuel use, CO₂ production, and operating expenses.”

Political Discussion and Automotive Pressure

Hybrid cars have lately been brought back into political discussions as automakers have lobbied the European Union to weaken CO₂ targets. A proposed prohibition on new internal combustion cars in 2035 has faced intense pressure from the car industry and opposition from member states with large automotive industries.

Several high-level officials have suggested PHEVs as a potential “flexibility” solution to include in the legislation.

An independent energy economics specialist, who was not involved with the study, called the analysis a “very useful contribution” after years in which parts of the automotive industry argued there was too little data to accurately evaluate actual CO2 output.

“These findings show, beyond any doubt, that the difference between official and real-world PHEV energy use and CO₂ output is significantly larger than for gasoline or conventional cars,” they stated. “Any regulatory adjustments concerning PHEVs should be implemented with extreme care and considering that data.”