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Plug-in hybrid cars produce almost 5x more global warming emissions than lab-reported data show, according to a recent report.

Growing Gap In Official and Actual CO2 Output

Statistics reveals that PHEVs release only one-fifth less CO₂ than traditional petrol and diesel vehicles, based on research carried out by a non-profit organization. That contrasts sharply with lab estimates, which assumed a three-quarters reduction in emissions.

Researchers examined information from onboard energy use meters of eight hundred thousand cars sold in the EU from 2021 and 2023. The team found that real-world CO₂ output from PHEVs in 2023 were nearly five times greater than lab estimates, up from three and a half times in 2021.

“Actual CO2 output are increasing, while lab-reported figures are falling,” stated a senior analyst participating in the report. “This discrepancy is growing and poses a significant issue. As a result, PHEVs emit almost as much as petrol vehicles.”

Primary Reasons Driving the Emissions Gap

Analysts attributed most of the difference to inflated estimates of the “utility factor” – the percentage of miles driven in electric power relative to overall distance. They found that just a quarter of driving was done in electric mode, whereas lab assumptions assumed over four-fifths.

Even, when running in electric mode, emission levels were significantly higher than lab projections. This occurred because electric motors were not strong sufficient to operate alone, resulting to engines burning fossil fuels for almost one-third of the distance completed in electric mode.

Policy and Financial Consequences

Based on calculations, the underestimation of PHEV CO2 output allowed several major carmaker companies to avoid more than €5bn in fines from 2021 and 2023, by falsely easing compliance with EU fleet-average CO₂ targets.

Furthermore, owners of PHEVs would pay approximately €500 extra per year in running costs than would be assumed under lab tests.

“The strong statements that automakers like to make about their plug-in hybrid cars are obviously way off the mark,” stated a transport expert. “Consumers are being duped into believing that by buying a PHEV, they are benefiting the environment and saving costs. Actually, PHEVs are only slightly improved than regular petrol and diesel cars in terms of fuel consumption, CO₂ emissions, and running costs.”

Policy Debate and Automotive Pressure

Plug-in hybrid cars have recently been brought again into policy discussions as carmakers have lobbied the EU to weaken CO₂ standards. A planned ban on sales of new internal combustion cars in 2035 has faced heavy lobbying from the car sector and resistance from member states with significant car industries.

Some senior politicians have proposed plug-in hybrids as a potential “compromise” option to include in the legislation.

An external energy policy specialist, who was not involved with the study, called the report a “highly valuable contribution” after years in which parts of the car sector argued there was insufficient data to accurately assess actual emissions.

“These findings show, without question, that the difference in official and real-world PHEV energy use and CO₂ output is much, much larger than for gasoline or diesel cars,” they stated. “Any policy adjustments concerning PHEVs should be made with utmost care and considering that data.”