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Plug-in hybrid cars produce almost 5x greater planet-heating pollution than lab-reported data show, according to a new report.

Growing Discrepancy Between Official and Actual CO2 Output

Statistics reveals that PHEVs release only one-fifth lower CO₂ than conventional gas and diesel cars, based on research carried out by a non-profit group. That differs sharply with laboratory tests, which suggested a three-quarters reduction in pollution.

Analysts studied information from onboard energy use meters of eight hundred thousand cars sold in the EU between 2021 and 2023. The team discovered that actual CO₂ emissions from PHEVs in 2023 were 4.9 times higher than lab figures, increased from 3.5 times in 2021.

“Real-world emissions are rising, while official figures are decreasing,” said a senior researcher participating in the study. “That discrepancy is growing and creates a significant issue. As a result, PHEVs pollute nearly as much as petrol vehicles.”

Primary Factors Driving the Emissions Gap

Researchers attributed the majority of the gap to overestimates of the “electric driving share” – the ratio of kilometers driven in battery power compared to overall distance. The team determined that just a quarter of travel was completed in electric mode, whereas official estimates assumed over four-fifths.

Even, when operating in electric mode, pollution levels were well above lab projections. This happened because electric motors were insufficiently powerful sufficient to operate independently, leading to engines using gasoline for nearly a third of the travel completed in EV mode.

Policy and Financial Implications

Based on calculations, the underestimation of PHEV CO2 output enabled four major carmaker groups to avoid more than €5bn in penalties between 2021 and 2023, by artificially easing adherence with EU fleet-average CO₂ targets.

Additionally, owners of PHEVs could pay about €500 more per year in operating costs than would be assumed under lab conditions.

“The strong claims that automakers often promote about their PHEV vehicles are clearly far from the mark,” commented a transport analyst. “Buyers are being duped into believing that by purchasing a PHEV, they are benefiting the environment and saving money. Actually, PHEVs are only slightly better than regular gas and diesel cars in terms of energy use, CO₂ emissions, and operating expenses.”

Political Debate and Industry Pressure

Plug-in hybrid vehicles have recently been drawn again into political discussions as carmakers have pressed the EU to relax CO₂ standards. A planned ban on new combustion engine cars in 2035 has faced heavy lobbying from the car sector and resistance from EU countries with large car manufacturing.

Several high-level politicians have proposed PHEVs as a potential “flexibility” solution to include in the legislation.

One external energy economics specialist, who was not involved with the research, called the analysis a “highly valuable addition” after a long period in which segments of the automotive industry claimed there was too little information to accurately evaluate actual emissions.

“The results show, beyond any doubt, that the gap in lab and real-world PHEV fuel consumption and CO₂ output is significantly greater than for gasoline or conventional vehicles,” they stated. “All regulatory changes regarding PHEVs should be made with utmost care and considering that data.”