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Plug-in hybrid cars release nearly 5x more global warming emissions than lab-reported data indicate, according to a new report.

Growing Gap Between Official and Real-World Emissions

Data shows that PHEVs release just one-fifth less CO₂ than conventional petrol and diesel vehicles, according to analysis carried out by a non-profit group. This contrasts significantly with lab tests, which suggested a 75% reduction in pollution.

Analysts studied data from in-vehicle energy use meters of 800,000 cars sold in Europe from 2021 and 2023. The team discovered that real-world CO₂ output from PHEVs in 2023 were 4.9 times higher than lab estimates, increased from three and a half times in 2021.

“Actual emissions are increasing, while official emissions are decreasing,” stated a lead analyst participating in the report. “This discrepancy is widening and creates a significant issue. As a result, PHEVs emit almost as heavily as petrol cars.”

Key Reasons Behind the Discrepancy

Analysts linked the majority of the difference to inflated estimates of the “utility factor” – the ratio of miles driven in battery mode relative to overall distance. The team determined that only 27% of driving was done in EV mode, while official assumptions assumed 84%.

Additionally, when operating in EV mode, emission amounts were well above official projections. That happened because EV motors were not strong enough to operate independently, leading to combustion motors using gasoline for almost one-third of the travel covered in electric mode.

Regulatory and Economic Consequences

Based on calculations, the lowballing of PHEV emissions allowed four large carmaker companies to escape more than €5bn in penalties from 2021 and 2023, by falsely easing compliance with EU average fleet CO₂ targets.

Furthermore, drivers of PHEVs would spend about €500 more annually in running costs than would be assumed under laboratory tests.

“The strong claims that automakers often promote about their plug-in hybrid vehicles are clearly far from the mark,” commented a automotive expert. “Buyers are being misled into thinking that by buying a PHEV, they are benefiting the environment and saving money. Actually, PHEVs are little better than standard petrol and diesel vehicles in terms of fuel consumption, CO₂ emissions, and running costs.”

Policy Debate and Industry Lobbying

Hybrid cars have recently been brought back into policy debates as automakers have lobbied the EU to weaken CO₂ standards. A planned prohibition on new combustion engine cars in 2035 has faced intense lobbying from the automotive industry and opposition from member states with large car industries.

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

One external energy economics expert, who was unaffiliated with the research, called the report a “highly valuable contribution” after years in which segments of the automotive industry argued there was insufficient data to accurately assess actual CO2 output.

“These findings show, without question, that the difference between official and actual PHEV fuel consumption and CO₂ emissions is much, much greater than for petrol or diesel cars,” they said. “Any policy changes concerning PHEVs should be implemented with extreme caution and considering this evidence.”