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Plug-in hybrid cars release almost 5x more global warming emissions than lab-reported figures indicate, according to a recent report.

Widening Discrepancy Between Official and Real-World Emissions

Data reveals that PHEVs emit only one-fifth less CO₂ than conventional petrol and diesel vehicles, based on analysis carried out by a non-profit organization. That differs significantly with lab estimates, which suggested a 75% reduction in pollution.

Researchers studied information from in-vehicle fuel consumption monitors of 800,000 vehicles sold in the EU 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.

“Real-world emissions are increasing, while lab-reported figures are falling,” stated a senior researcher involved in the report. “This discrepancy is widening and creates a significant problem. Consequently, PHEVs emit nearly as much as gasoline vehicles.”

Primary Reasons Driving the Discrepancy

Researchers linked most of the gap to inflated estimates of the “utility factor” – the ratio of miles travelled in battery mode compared to overall mileage. They determined that only a quarter of travel was completed in electric mode, whereas official assumptions assumed 84%.

Additionally, when operating in electric mode, emission amounts were significantly higher than official estimates. That happened because EV motors were insufficiently powerful sufficient to function alone, resulting to combustion motors burning fossil fuels for almost a third of the distance covered in EV mode.

Regulatory and Economic Implications

Based on calculations, the lowballing of PHEV CO2 output enabled several large carmaker groups to avoid over €5bn in fines from 2021 and 2023, by falsely easing compliance with EU average fleet CO₂ standards.

Additionally, drivers of PHEVs would spend approximately €500 more annually in operating costs than is assumed under laboratory conditions.

“The strong claims that automakers often promote about their PHEV cars are clearly way off the truth,” commented a automotive analyst. “Consumers are being duped into thinking that by purchasing a PHEV, they are helping the planet and saving money. Actually, PHEVs are only slightly improved than standard petrol and diesel cars in terms of energy use, CO₂ emissions, and operating costs.”

Policy Debate and Industry Lobbying

Plug-in hybrid cars have recently been brought back into policy debates as automakers have lobbied the European Union to relax CO₂ standards. A planned ban on sales of new internal combustion vehicles in 2035 has faced intense pressure from the automotive sector and opposition from member states with large car manufacturing.

Several senior officials have proposed PHEVs as a potential “compromise” solution to introduce in the legislation.

An external energy economics specialist, who was unaffiliated with the research, called the analysis a “highly valuable contribution” after years in which parts of the automotive sector argued there was insufficient information to accurately assess actual emissions.

“The results demonstrate, beyond any doubt, that the difference between lab and actual PHEV fuel consumption and CO₂ output is significantly greater than for petrol or diesel cars,” the expert stated. “All regulatory adjustments concerning PHEVs should be implemented with extreme care and in the light of that data.”