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Plug-in hybrid cars release nearly five times more global warming pollution than lab-reported data show, according to a recent analysis.

Widening Discrepancy Between Lab and Real-World CO2 Output

Data reveals that PHEVs release only 19% less CO₂ than conventional petrol and diesel vehicles, according to analysis conducted by a non-profit organization. That differs sharply with laboratory estimates, which assumed a 75% decrease in pollution.

Researchers examined data from in-vehicle fuel consumption monitors of 800,000 cars sold in Europe between 2021 and 2023. The team discovered that real-world CO₂ output from PHEVs in 2023 were nearly five times higher than official figures, up from 3.5 times in 2021.

“Actual emissions are increasing, while official figures are decreasing,” said a lead analyst participating in the report. “This discrepancy is widening and poses a significant problem. Consequently, PHEVs pollute nearly as heavily as gasoline vehicles.”

Key Reasons Driving the Emissions Gap

Analysts attributed most of the gap to overestimates of the “utility factor” – the percentage of miles travelled in electric mode relative to overall distance. They determined that just 27% of travel was completed in EV mode, while lab estimates assumed 84%.

Even, when operating in EV mode, pollution amounts were well above official estimates. This occurred because electric motors were insufficiently powerful enough to operate independently, resulting to engines using fossil fuels for almost a third of the distance completed in electric mode.

Policy and Economic Implications

According to calculations, the underestimation of PHEV CO2 output allowed several large automaker companies to escape more than €5bn in penalties between 2021 and 2023, by artificially simplifying adherence with EU average fleet CO₂ targets.

Furthermore, owners of PHEVs would pay about €500 extra annually in running expenses than is assumed under laboratory tests.

“The strong statements that manufacturers like to make about their PHEV cars are obviously far from the truth,” stated a automotive expert. “Consumers are being duped into thinking that by purchasing a PHEV, they are benefiting the environment and cutting costs. Actually, PHEVs are only slightly improved than regular petrol and diesel cars in terms of fuel consumption, CO₂ production, and running costs.”

Political Discussion and Automotive Pressure

Plug-in hybrid cars have lately been drawn back into political discussions as automakers have lobbied the EU to relax CO₂ targets. A planned prohibition on sales of new internal combustion cars in 2035 has faced intense pressure from the automotive sector and resistance from member states with large car manufacturing.

Several senior officials have suggested plug-in hybrids as a potential “flexibility” option to include in the legislation.

An external energy economics expert, who was not involved with the research, described the report a “highly valuable contribution” after a long period in which parts of the car sector argued there was too little information to properly evaluate real-world CO2 output.

“The results demonstrate, without question, that the gap in official and actual PHEV fuel consumption and CO₂ output is significantly larger than for petrol or diesel cars,” they stated. “Any regulatory changes concerning PHEVs should be made with extreme care and considering that evidence.”