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Plug-in hybrid cars produce almost five times more global warming emissions than lab-reported data show, according to a recent report.

Growing Discrepancy Between Official and Actual Emissions

Statistics shows that PHEVs emit only one-fifth less CO₂ than traditional petrol and diesel cars, based on research conducted by a advocacy group. This differs sharply with laboratory tests, which assumed a three-quarters reduction in pollution.

Researchers examined information from in-vehicle fuel consumption monitors of 800,000 cars sold in Europe between 2021 and 2023. They discovered that actual CO₂ output from PHEVs in 2023 were 4.9 times higher than lab estimates, up from 3.5 times in 2021.

“Actual emissions are rising, while official figures are decreasing,” stated a senior researcher involved in the study. “This discrepancy is widening and poses a significant issue. As a result, PHEVs pollute almost as much as gasoline cars.”

Primary Reasons Behind the Discrepancy

Researchers linked most of the difference to inflated estimates of the “electric driving share” – the ratio of kilometers travelled in electric mode relative to total mileage. They determined that just 27% of driving was done in electric mode, while official estimates assumed over four-fifths.

Even, when running in EV mode, emission amounts were significantly higher than lab projections. That happened because EV motors were not strong enough to operate alone, leading to engines using fossil fuels for almost one-third of the travel covered in EV mode.

Policy and Economic Consequences

According to calculations, the underestimation of PHEV emissions enabled four major automaker groups to avoid over €5bn in penalties between 2021 and 2023, by falsely easing adherence with European Union fleet-average CO₂ targets.

Furthermore, drivers of PHEVs would pay about €500 extra annually in operating costs than would be estimated under lab conditions.

“The bold claims that automakers often promote about their PHEV cars are obviously far from the mark,” commented a automotive analyst. “Buyers are being duped into believing that by buying a PHEV, they are helping the environment and cutting money. In reality, PHEVs are only slightly improved than standard gas and diesel cars in terms of fuel consumption, CO₂ emissions, and operating expenses.”

Policy Debate and Automotive Pressure

Plug-in hybrid cars have recently been brought back into political debates as automakers have pressed the European Union to weaken CO₂ targets. A planned prohibition on sales of new combustion engine vehicles in 2035 has faced heavy lobbying from the automotive sector and resistance from EU countries with significant car manufacturing.

Several high-level officials have suggested PHEVs as a possible “flexibility” solution to include in the regulation.

One external energy policy expert, who was not involved with the study, called the report a “very useful addition” after a long period in which parts of the automotive industry claimed there was insufficient data to properly assess actual CO2 output.

“The results show, without question, that the gap in lab and actual PHEV energy use and CO₂ output is much, much larger than for gasoline or conventional vehicles,” they said. “All policy changes regarding PHEVs should be made with extreme care and considering that evidence.”