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Plug-in hybrid cars emit nearly 5x greater global warming emissions than lab-reported figures indicate, according to a new analysis.

Growing Discrepancy In Lab and Real-World CO2 Output

Data shows that PHEVs emit just 19% lower CO₂ than conventional petrol and diesel cars, according to research carried out by a non-profit organization. That contrasts sharply with laboratory estimates, which suggested a three-quarters reduction in emissions.

Researchers examined data from in-vehicle fuel consumption meters of 800,000 vehicles sold in the EU between 2021 and 2023. The team discovered that real-world CO₂ output from PHEVs in 2023 were 4.9 times greater than official estimates, up from 3.5 times in 2021.

“Actual CO2 output are increasing, while lab-reported emissions are decreasing,” said a lead analyst involved in the study. “This discrepancy is widening and poses a significant problem. Consequently, PHEVs emit almost as much as gasoline vehicles.”

Primary Factors Behind the Emissions Gap

Analysts attributed most of the difference to overestimates of the “utility factor” – the ratio of kilometers driven in electric power relative to overall distance. They determined that only 27% of driving was done in electric mode, whereas lab estimates assumed 84%.

Additionally, when running in EV mode, emission levels were well above lab estimates. This occurred because electric motors were insufficiently powerful sufficient to function alone, resulting to combustion motors burning fossil fuels for nearly one-third of the distance covered in electric mode.

Regulatory and Financial Consequences

According to estimates, the lowballing of PHEV CO2 output allowed several large automaker companies to avoid over €5bn in fines from 2021 and 2023, by artificially simplifying adherence with EU fleet-average CO₂ targets.

Furthermore, drivers of PHEVs would pay about €500 more per year in running costs than would be estimated under lab conditions.

“The bold claims that automakers like to make about their plug-in hybrid vehicles are obviously far from the mark,” commented a automotive analyst. “Consumers are being misled into thinking that by purchasing a PHEV, they are helping the environment and saving costs. In reality, PHEVs are little improved than standard petrol and diesel vehicles in terms of fuel use, CO₂ emissions, and operating expenses.”

Political Discussion and Automotive Pressure

Plug-in hybrid vehicles have recently been brought back into political debates as carmakers have lobbied the European Union to relax CO₂ standards. A proposed ban on new internal combustion vehicles in 2035 has faced intense lobbying from the car sector and resistance from member states with large automotive manufacturing.

Some senior officials have suggested PHEVs as a potential “compromise” option to introduce in the regulation.

An independent energy economics specialist, who was not involved with the study, called the report a “highly valuable contribution” after years in which segments of the automotive sector claimed there was too little information to properly assess real-world emissions.

“The results show, beyond any doubt, that the difference in official and actual PHEV energy use and CO₂ emissions is significantly greater than for petrol or conventional cars,” the expert said. “Any regulatory adjustments concerning PHEVs should be implemented with extreme care and considering this data.”