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Plug-in hybrid electric vehicles produce almost 5x greater global warming emissions than lab-reported figures indicate, according to a new report.

Growing Discrepancy Between Lab and Real-World CO2 Output

Data reveals that PHEVs emit just 19% lower CO₂ than traditional gas and diesel vehicles, based on research conducted by a non-profit organization. This contrasts significantly with laboratory estimates, which suggested a 75% decrease in pollution.

Researchers studied data from in-vehicle fuel consumption monitors of 800,000 cars registered in Europe from 2021 and 2023. They discovered that real-world CO₂ emissions from PHEVs in 2023 were 4.9 times higher than official estimates, up from 3.5 times in 2021.

“Actual CO2 output are increasing, while official emissions are decreasing,” said a senior researcher involved in the study. “This gap is widening and creates a significant issue. Consequently, PHEVs pollute almost as heavily as petrol cars.”

Key Reasons Driving the Emissions Gap

Researchers attributed the majority of the difference to overestimates of the “utility factor” – the ratio of kilometers driven in electric mode compared to total mileage. They determined that only 27% of travel was completed in electric mode, while official assumptions assumed over four-fifths.

Additionally, when running in EV mode, pollution amounts were significantly higher than official estimates. That occurred because electric motors were insufficiently powerful enough to function alone, leading to combustion motors burning gasoline for almost one-third of the travel covered in EV mode.

Policy and Financial Consequences

Based on estimates, the lowballing of PHEV emissions allowed four large automaker groups to avoid more than €5bn in penalties between 2021 and 2023, by artificially easing compliance with European Union average fleet CO₂ targets.

Additionally, owners of PHEVs would pay approximately €500 extra annually in operating costs than would be estimated under lab conditions.

“The strong statements that manufacturers often promote about their PHEV cars are obviously far from the mark,” commented a automotive analyst. “Consumers are being duped into thinking that by purchasing a PHEV, they are helping the planet and saving costs. Actually, PHEVs are only slightly improved than regular gas and diesel vehicles in terms of fuel consumption, CO₂ emissions, and operating costs.”

Political Discussion and Industry Lobbying

Plug-in hybrid cars have lately been drawn back into political discussions as automakers have lobbied the EU to weaken CO₂ targets. A planned ban on sales of new combustion engine vehicles in 2035 has faced heavy pressure from the automotive sector and opposition from EU countries with significant car industries.

Several senior politicians have suggested plug-in hybrids as a possible “flexibility” solution to include in the regulation.

One independent energy policy expert, who was not involved with the research, described the analysis a “very useful contribution” after a long period in which parts of the car sector claimed there was too little information to accurately assess real-world emissions.

“These findings show, without question, that the gap between official and actual PHEV fuel consumption and CO₂ emissions is much, much greater than for petrol or conventional vehicles,” they said. “Any regulatory adjustments concerning PHEVs should be implemented with extreme caution and in the light of that data.”