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Plug-in hybrid cars emit nearly five times more planet-heating emissions than official data show, according to a recent report.

Growing Discrepancy Between Lab and Actual Emissions

Statistics reveals that PHEVs release only one-fifth less CO₂ than conventional gas and diesel cars, based on analysis conducted by a advocacy organization. That contrasts sharply with laboratory tests, which suggested a three-quarters decrease in pollution.

Researchers examined data from onboard fuel consumption monitors of 800,000 cars sold in Europe from 2021 and 2023. They found that actual CO₂ output from PHEVs in 2023 were 4.9 times higher than lab estimates, increased from 3.5 times in 2021.

“Actual CO2 output are increasing, while official figures are decreasing,” said a senior analyst involved in the study. “That gap is growing and poses a serious problem. As a result, PHEVs emit almost as much as petrol cars.”

Key Factors Behind the Emissions Gap

Researchers linked most of the difference to overestimates of the “utility factor” – the ratio of kilometers driven in electric power compared to total mileage. The team determined that just 27% of driving was completed in electric mode, while official estimates suggested 84%.

Even, when running in electric mode, emission levels were well above lab projections. That occurred because electric motors were insufficiently powerful enough to operate independently, leading to combustion motors burning gasoline for nearly a third of the distance completed in electric mode.

Regulatory and Economic Implications

Based on estimates, the lowballing of PHEV emissions allowed four large carmaker groups to escape over €5bn in penalties from 2021 and 2023, by artificially simplifying compliance with European Union fleet-average CO₂ standards.

Additionally, drivers of PHEVs would spend approximately €500 more per year in running expenses than would be estimated under laboratory conditions.

“The bold statements that automakers like to make about their plug-in hybrid cars are obviously far from the mark,” commented a transport analyst. “Consumers are being misled into thinking that by purchasing a PHEV, they are helping the planet and cutting costs. Actually, PHEVs are only slightly better than regular petrol and diesel vehicles in terms of fuel use, CO₂ emissions, and operating expenses.”

Policy Debate and Automotive Lobbying

Plug-in hybrid cars have lately been drawn back into policy debates as automakers have lobbied the European Union to weaken CO₂ targets. A proposed prohibition on new internal combustion cars in 2035 has faced heavy lobbying from the automotive sector and resistance from EU countries with significant car industries.

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

An independent energy policy specialist, who was unaffiliated with the study, described the report a “highly valuable addition” after a long period in which parts of the automotive industry claimed there was too little information to properly evaluate real-world emissions.

“The results demonstrate, beyond any doubt, that the difference in official and actual PHEV energy use and CO₂ output is much, much larger than for petrol or conventional cars,” they said. “All policy changes regarding PHEVs should be implemented with extreme care and considering that data.”