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

Widening Discrepancy Between Official and Actual Emissions

Data shows that PHEVs release only 19% lower CO₂ than traditional petrol and diesel cars, based on research carried out by a advocacy group. That differs sharply with lab estimates, which suggested a three-quarters decrease in emissions.

Analysts examined data from in-vehicle energy use meters of 800,000 cars registered in the EU between 2021 and 2023. They discovered that actual CO₂ emissions from PHEVs in 2023 were nearly five times greater than official figures, increased from three and a half times in 2021.

“Actual CO2 output are increasing, while lab-reported figures are falling,” said a senior researcher participating in the report. “This gap is widening and creates a serious issue. Consequently, PHEVs pollute almost as heavily as gasoline cars.”

Key Reasons Driving the Discrepancy

Researchers linked the majority of the gap to inflated estimates of the “electric driving share” – the percentage of kilometers driven in electric power relative to total distance. The team found that just 27% of driving was done in electric mode, whereas lab assumptions assumed over four-fifths.

Even, when operating in electric mode, pollution amounts were significantly higher than lab estimates. This happened because electric motors were insufficiently powerful enough to function alone, leading to combustion motors burning fossil fuels for nearly a third of the distance completed in EV mode.

Regulatory and Economic Implications

According to estimates, the lowballing of PHEV emissions allowed four major automaker companies to escape more than €5bn in fines from 2021 and 2023, by artificially simplifying adherence with EU fleet-average CO₂ targets.

Furthermore, drivers of PHEVs would pay about €500 more annually in running costs than is assumed under lab conditions.

“The strong statements that automakers often promote about their PHEV vehicles are obviously way off the truth,” stated a automotive expert. “Consumers are being duped into believing that by buying a PHEV, they are helping the environment and cutting costs. Actually, PHEVs are little improved than regular petrol and diesel vehicles in terms of fuel consumption, CO₂ production, and running costs.”

Political Debate and Industry Lobbying

Plug-in hybrid cars have recently been drawn again into policy debates as carmakers have pressed the European Union to relax CO₂ targets. A proposed prohibition on sales of new combustion engine vehicles in 2035 has faced heavy lobbying from the car sector and opposition from EU countries with significant automotive manufacturing.

Several senior politicians have suggested plug-in hybrids as a potential “flexibility” solution to introduce in the legislation.

An external energy policy specialist, who was not involved with the study, called the report a “very useful contribution” after a long period in which segments of the car industry claimed there was insufficient information to properly evaluate real-world CO2 output.

“These findings show, beyond any doubt, that the gap between official and real-world PHEV fuel consumption and CO₂ emissions is significantly greater than for gasoline or diesel vehicles,” they stated. “Any regulatory changes concerning PHEVs should be implemented with utmost care and considering this data.”