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Plug-in hybrid electric vehicles produce almost five times greater planet-heating pollution than official figures show, according to a new report.

Widening Gap In Official and Actual CO2 Output

Data reveals that PHEVs emit just one-fifth lower CO₂ than conventional gas and diesel vehicles, based on analysis carried out by a non-profit group. That differs sharply with lab estimates, which suggested a three-quarters decrease in emissions.

Researchers studied data from in-vehicle fuel consumption meters of 800,000 vehicles registered in Europe between 2021 and 2023. The team found that real-world CO₂ emissions from PHEVs in 2023 were 4.9 times greater than lab figures, increased from three and a half times in 2021.

“Actual emissions are increasing, while official figures are decreasing,” stated a lead analyst involved in the report. “That discrepancy is growing and poses a significant problem. Consequently, PHEVs pollute almost as much as petrol cars.”

Key Factors Driving the Discrepancy

Researchers linked the majority of the gap to inflated estimates of the “electric driving share” – the percentage of miles driven in battery power relative to overall mileage. They determined that only a quarter of driving was done in EV mode, whereas lab estimates suggested over four-fifths.

Even, when running in EV mode, pollution amounts were significantly higher than official projections. This happened because electric motors were not strong sufficient to operate independently, leading to combustion motors burning gasoline for nearly a third of the distance completed in electric mode.

Regulatory and Financial Consequences

According to calculations, the underestimation of PHEV emissions allowed several major carmaker companies to avoid more than €5bn in penalties from 2021 and 2023, by falsely easing compliance with European Union average fleet CO₂ targets.

Additionally, drivers of PHEVs would pay about €500 extra per year in operating expenses than would be assumed under laboratory tests.

“The strong statements that manufacturers like to make about their plug-in hybrid cars are clearly way off the truth,” commented a transport analyst. “Buyers are being duped into believing that by purchasing a PHEV, they are helping the environment and cutting money. In reality, PHEVs are only slightly improved than regular petrol and diesel cars in terms of energy use, CO₂ emissions, and operating costs.”

Political Debate and Industry Pressure

Plug-in hybrid cars have lately been drawn back into political debates as carmakers have pressed the European Union to relax CO₂ targets. A proposed ban on sales of new internal combustion cars in 2035 has faced heavy pressure from the automotive sector and resistance from EU countries with significant car industries.

Several high-level officials have proposed plug-in hybrids as a potential “compromise” solution to introduce in the regulation.

An external energy policy expert, who was not involved with the study, called the analysis a “highly valuable contribution” after a long period in which parts of the automotive sector argued there was too little information to accurately evaluate real-world CO2 output.

“These findings show, beyond any doubt, that the difference in official and real-world PHEV energy use and CO₂ emissions is much, much greater than for petrol or diesel cars,” they stated. “Any regulatory adjustments regarding PHEVs should be made with utmost caution and considering this data.”