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Plug-in hybrid cars release almost five times greater planet-heating emissions than lab-reported data show, according to a new analysis.

Widening Gap In Lab and Actual Emissions

Data shows that PHEVs release just one-fifth less CO₂ than traditional gas and diesel vehicles, according to analysis carried out by a non-profit group. That contrasts significantly with laboratory estimates, which assumed a three-quarters decrease in pollution.

Researchers examined data from in-vehicle fuel consumption meters of 800,000 cars sold in the EU between 2021 and 2023. The team discovered that actual CO₂ output from PHEVs in 2023 were 4.9 times greater than lab figures, up from three and a half times in 2021.

“Real-world emissions are rising, while official emissions are decreasing,” said a lead analyst involved in the study. “This gap is widening and creates a significant issue. As a result, PHEVs pollute nearly as much as petrol vehicles.”

Primary Factors Behind the Emissions Gap

Researchers linked most of the difference to inflated estimates of the “electric driving share” – the percentage of kilometers driven in electric mode relative to overall mileage. They found that only 27% of travel was completed in electric mode, whereas lab estimates suggested 84%.

Additionally, when operating in EV mode, pollution levels were well above lab estimates. That happened because electric motors were not strong enough to operate alone, leading to engines burning fossil fuels for almost a third of the travel covered in EV mode.

Policy and Economic Consequences

According to estimates, the underestimation of PHEV CO2 output enabled four large carmaker companies to escape over €5bn in fines between 2021 and 2023, by falsely easing adherence with European Union fleet-average CO₂ targets.

Additionally, drivers of PHEVs would spend about €500 more annually in running costs than is estimated under lab tests.

“The strong claims that manufacturers like to make about their PHEV vehicles are obviously way off the mark,” commented a automotive analyst. “Consumers are being misled into thinking that by buying a PHEV, they are benefiting the planet and saving costs. Actually, PHEVs are only slightly improved than regular gas and diesel vehicles in terms of energy consumption, CO₂ emissions, and running costs.”

Political Debate and Automotive Lobbying

Plug-in hybrid vehicles have recently been brought back into political debates as carmakers have lobbied the EU to weaken CO₂ standards. A proposed ban on sales of new combustion engine vehicles in 2035 has faced heavy lobbying from the automotive industry and resistance from member states with significant car manufacturing.

Several senior politicians have suggested PHEVs as a possible “compromise” option to include in the legislation.

An independent energy economics expert, who was not involved with the research, called the report a “highly valuable contribution” after years in which parts of the car industry claimed there was insufficient data to properly evaluate actual CO2 output.

“These findings show, without question, that the gap in official and real-world PHEV energy use and CO₂ emissions is much, much larger than for petrol or conventional vehicles,” the expert said. “All policy changes concerning PHEVs should be implemented with utmost care and considering this data.”