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Plug-in hybrid electric vehicles release almost 5x greater global warming emissions than official figures indicate, as per a new analysis.

Growing Gap Between Official and Real-World Emissions

Statistics reveals that PHEVs release just one-fifth less CO₂ than traditional petrol and diesel cars, according to analysis carried out by a non-profit organization. That contrasts significantly with laboratory estimates, which assumed a 75% decrease in pollution.

Analysts studied information from in-vehicle fuel consumption monitors of 800,000 vehicles registered in the EU from 2021 and 2023. They found that real-world CO₂ emissions from PHEVs in 2023 were nearly five times higher than lab estimates, up from 3.5 times in 2021.

“Real-world CO2 output are rising, while lab-reported figures are falling,” said a senior researcher involved in the study. “That discrepancy is widening and creates a significant issue. Consequently, PHEVs pollute nearly as heavily as gasoline vehicles.”

Key Factors Behind the Emissions Gap

Researchers linked most of the gap to inflated estimates of the “utility factor” – the ratio of miles travelled in battery power relative to overall mileage. The team determined that just 27% of driving was done in EV mode, whereas official estimates assumed 84%.

Additionally, when running in EV mode, pollution levels were well above official projections. That happened because EV motors were not strong enough to function independently, resulting to engines using fossil fuels for almost one-third of the travel covered in electric mode.

Regulatory and Financial Consequences

According to calculations, the underestimation of PHEV emissions allowed several major automaker groups to escape more than €5bn in fines from 2021 and 2023, by artificially simplifying compliance with European Union average fleet CO₂ targets.

Furthermore, drivers of PHEVs would pay about €500 more annually in running expenses than would be estimated under lab tests.

“The strong claims that manufacturers like to make about their PHEV vehicles are obviously way off the truth,” stated a transport expert. “Buyers are being misled into believing that by purchasing a PHEV, they are benefiting the environment and cutting costs. In reality, PHEVs are little better than regular petrol and diesel vehicles in terms of fuel use, CO₂ emissions, and running costs.”

Policy Discussion and Industry Pressure

Plug-in hybrid vehicles have lately been drawn again into political debates as carmakers have pressed the EU to relax CO₂ targets. A planned ban on new combustion engine vehicles in 2035 has faced heavy lobbying from the automotive sector and opposition from EU countries with significant automotive manufacturing.

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

An independent energy economics expert, who was not involved with the research, described the report a “very useful addition” after years in which segments of the automotive sector claimed there was insufficient data to properly evaluate real-world CO2 output.

“The results show, without question, that the gap between official and real-world PHEV fuel consumption and CO₂ output is much, much greater than for petrol or conventional vehicles,” the expert said. “Any regulatory adjustments concerning PHEVs should be implemented with utmost caution and in the light of this evidence.”