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Plug-in hybrid cars produce almost five times greater global warming pollution than official figures indicate, according to a new analysis.

Widening Gap In Lab and Real-World Emissions

Data reveals that PHEVs release just 19% less CO₂ than conventional gas and diesel vehicles, based on research conducted by a advocacy group. This differs sharply with laboratory estimates, which assumed a 75% decrease in emissions.

Researchers examined data from onboard energy use monitors of eight hundred thousand cars sold in the EU between 2021 and 2023. They found 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 emissions are increasing, while official emissions are decreasing,” said a lead researcher participating in the study. “This gap is growing and poses a significant problem. As a result, PHEVs pollute nearly as much as gasoline vehicles.”

Primary Factors Behind the Emissions Gap

Analysts attributed most of the difference to overestimates of the “electric driving share” – the percentage of kilometers driven in battery mode compared to overall distance. The team determined that just a quarter of driving was completed in EV mode, whereas official assumptions assumed over four-fifths.

Even, when running in electric mode, emission levels were significantly higher than lab projections. That occurred because EV motors were not strong enough to function alone, leading to engines burning fossil fuels for nearly one-third of the travel completed in EV mode.

Regulatory and Financial Consequences

Based on calculations, the underestimation of PHEV emissions enabled several major carmaker companies to avoid over €5bn in fines from 2021 and 2023, by falsely easing compliance with European Union fleet-average CO₂ standards.

Furthermore, owners of PHEVs would spend about €500 extra annually in running costs than would be estimated under laboratory conditions.

“The bold claims that automakers often promote about their PHEV vehicles are obviously far from the mark,” stated a transport analyst. “Consumers are being duped into believing that by purchasing a PHEV, they are helping the planet and saving costs. Actually, PHEVs are only slightly better than regular petrol and diesel vehicles in terms of energy use, CO₂ production, and operating expenses.”

Policy Debate and Industry Lobbying

Hybrid cars have recently been drawn again into political discussions as carmakers have lobbied the EU to weaken CO₂ standards. A proposed prohibition on new internal combustion vehicles in 2035 has faced intense pressure from the automotive sector and resistance from EU countries with large automotive manufacturing.

Some senior politicians have proposed plug-in hybrids as a possible “compromise” solution to introduce in the regulation.

An independent energy economics specialist, who was not involved with the study, called the report a “very useful contribution” after years in which segments of the automotive industry argued there was insufficient information to accurately assess real-world CO2 output.

“These findings demonstrate, beyond any doubt, that the gap in official and actual PHEV fuel consumption and CO₂ output is much, much larger than for gasoline or conventional cars,” they stated. “Any policy changes concerning PHEVs should be made with utmost care and in the light of this data.”