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Plug-in hybrid cars release almost 5x more planet-heating emissions than lab-reported data indicate, according to a recent report.

Widening Discrepancy Between Official and Real-World CO2 Output

Data shows that PHEVs release just 19% lower CO₂ than traditional petrol and diesel vehicles, based on analysis carried out by a non-profit organization. That contrasts significantly with laboratory estimates, which assumed a 75% reduction in emissions.

Researchers examined information from onboard fuel consumption monitors of eight hundred thousand vehicles sold in the EU from 2021 and 2023. The team discovered that actual CO₂ output from PHEVs in 2023 were 4.9 times higher than official estimates, increased from 3.5 times in 2021.

“Real-world CO2 output are increasing, while lab-reported figures are decreasing,” stated a senior analyst involved in the study. “This gap is widening and creates a significant problem. Consequently, PHEVs emit almost as heavily as petrol vehicles.”

Primary Reasons Behind the Emissions Gap

Researchers linked the majority of the difference to inflated estimates of the “electric driving share” – the percentage of kilometers travelled in battery mode relative to total mileage. The team found that only 27% of driving was done in EV mode, whereas official estimates assumed 84%.

Even, when running in EV mode, pollution amounts were significantly higher than lab estimates. This happened because EV motors were insufficiently powerful enough to operate alone, leading to combustion motors using gasoline for nearly a third of the travel completed in EV mode.

Regulatory and Economic Consequences

Based on calculations, the underestimation of PHEV CO2 output enabled several large carmaker groups to escape over €5bn in penalties between 2021 and 2023, by artificially easing adherence with European Union average fleet CO₂ standards.

Furthermore, owners of PHEVs would pay approximately €500 more per year in operating costs than would be assumed under laboratory tests.

“The strong statements that manufacturers often promote about their plug-in hybrid vehicles are clearly way off the mark,” stated a transport analyst. “Buyers are being misled into thinking that by buying a PHEV, they are benefiting the planet and cutting money. In reality, PHEVs are only slightly better than standard gas and diesel cars in terms of fuel use, CO₂ emissions, and running costs.”

Policy Discussion and Automotive Pressure

Hybrid vehicles have lately been brought back into policy discussions as carmakers have lobbied the European Union to weaken CO₂ standards. A planned prohibition on sales of new combustion engine vehicles in 2035 has faced intense lobbying from the car sector and resistance from member states with significant car manufacturing.

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

One independent energy economics expert, who was not involved with the study, described the report a “highly valuable contribution” after a long period in which parts of the automotive sector argued there was insufficient data to accurately evaluate actual CO2 output.

“These findings demonstrate, beyond any doubt, that the difference between official and real-world PHEV energy use and CO₂ emissions is significantly greater than for petrol or conventional vehicles,” the expert stated. “Any policy adjustments concerning PHEVs should be made with utmost care and considering this evidence.”