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Plug-in hybrid electric vehicles produce almost 5x more planet-heating emissions than official data show, according to a new report.

Growing Gap Between Official and Real-World Emissions

Data shows that PHEVs release only 19% less CO₂ than conventional petrol and diesel cars, based on research conducted by a non-profit group. That contrasts significantly with laboratory estimates, which assumed a 75% reduction in pollution.

Analysts studied information from onboard fuel consumption meters of 800,000 cars sold in Europe between 2021 and 2023. The team discovered that actual CO₂ output from PHEVs in 2023 were 4.9 times higher than official estimates, up from three and a half times in 2021.

“Real-world CO2 output are increasing, while official emissions are falling,” stated a lead researcher participating in the report. “This gap is widening and poses a significant issue. As a result, PHEVs emit nearly as much as gasoline cars.”

Primary Factors Behind the Emissions Gap

Researchers attributed most of the difference to inflated estimates of the “electric driving share” – the percentage of miles travelled in battery mode relative to total distance. They found that only 27% of driving was done in electric mode, whereas lab assumptions suggested 84%.

Even, when operating in electric mode, pollution amounts were well above lab projections. This occurred because EV motors were not strong sufficient to operate alone, resulting to combustion motors using fossil fuels for nearly a third of the distance completed in electric mode.

Policy and Economic Consequences

Based on estimates, the lowballing of PHEV emissions enabled four large automaker groups to escape more than €5bn in penalties from 2021 and 2023, by artificially easing compliance with European Union fleet-average CO₂ standards.

Furthermore, drivers of PHEVs could spend approximately €500 extra per year in running expenses than is assumed under lab tests.

“The bold statements that manufacturers like to make about their PHEV cars are clearly far from the truth,” stated a transport analyst. “Buyers are being duped into believing that by purchasing a PHEV, they are benefiting the planet and cutting money. Actually, PHEVs are little better than regular gas and diesel cars in terms of fuel use, CO₂ production, and operating costs.”

Political Debate and Automotive Lobbying

Plug-in hybrid cars have lately been drawn back into political debates as carmakers have lobbied the European Union to weaken CO₂ standards. A planned ban on new internal combustion cars in 2035 has faced heavy lobbying from the car industry and opposition from EU countries with large car industries.

Several high-level officials have suggested plug-in hybrids as a possible “flexibility” option to introduce in the legislation.

One external energy economics expert, who was unaffiliated with the study, described the analysis a “highly valuable contribution” after a long period in which parts of the automotive industry claimed there was insufficient data to properly assess actual CO2 output.

“The results demonstrate, without question, that the gap between lab and actual PHEV energy use and CO₂ output is significantly larger than for petrol or conventional vehicles,” the expert said. “Any policy changes concerning PHEVs should be made with extreme care and in the light of this data.”