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Plug-in hybrid cars produce almost five times greater global warming emissions than lab-reported data show, according to a recent analysis.

Growing Discrepancy In Lab and Real-World CO2 Output

Data shows that PHEVs emit just one-fifth less CO₂ than traditional petrol and diesel vehicles, according to research conducted by a non-profit group. This contrasts significantly with lab estimates, which suggested a 75% reduction in pollution.

Analysts studied data from in-vehicle energy use meters of eight hundred thousand cars sold in Europe between 2021 and 2023. The team found that real-world CO₂ emissions from PHEVs in 2023 were 4.9 times higher than official estimates, increased from 3.5 times in 2021.

“Real-world CO2 output are rising, while lab-reported emissions are decreasing,” stated a lead analyst participating in the report. “That discrepancy is widening and creates a significant problem. Consequently, PHEVs pollute nearly as much as petrol vehicles.”

Primary Factors Driving the Emissions Gap

Analysts attributed the majority of the difference to overestimates of the “utility factor” – the percentage of miles driven in electric power compared to total distance. They found that only a quarter of driving was completed in electric mode, whereas lab assumptions suggested 84%.

Even, when operating in EV mode, emission amounts were well above lab projections. That happened because electric motors were not strong sufficient to operate alone, leading to combustion motors using gasoline for almost a third of the travel completed in EV mode.

Policy and Financial Implications

Based on estimates, the underestimation of PHEV CO2 output allowed four major automaker groups to avoid over €5bn in penalties from 2021 and 2023, by falsely simplifying compliance with EU average fleet CO₂ standards.

Furthermore, owners of PHEVs would spend about €500 more per year in operating costs than is estimated under laboratory conditions.

“The strong statements that manufacturers like to make about their PHEV vehicles are clearly far from the mark,” stated a transport analyst. “Buyers are being misled into believing that by buying a PHEV, they are benefiting the environment and cutting costs. Actually, PHEVs are little improved than regular gas and diesel cars in terms of energy use, CO₂ production, and running expenses.”

Political Debate and Automotive Pressure

Plug-in hybrid cars have lately been brought again into policy debates as carmakers have pressed the European Union to weaken CO₂ standards. A planned prohibition on new combustion engine vehicles in 2035 has faced heavy lobbying from the automotive industry and resistance from member states with large automotive industries.

Some high-level politicians have suggested plug-in hybrids as a potential “flexibility” solution to introduce in the legislation.

An independent energy policy expert, who was unaffiliated with the study, described the report a “highly valuable addition” after a long period in which segments of the automotive sector argued there was too little information to accurately assess actual CO2 output.

“These findings demonstrate, beyond any doubt, that the difference between lab and actual PHEV energy use and CO₂ output is significantly larger than for gasoline or conventional cars,” the expert stated. “All policy changes regarding PHEVs should be made with extreme care and in the light of that evidence.”