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Plug-in hybrid electric vehicles release almost five times greater planet-heating pollution than lab-reported figures show, according to a new analysis.

Growing Discrepancy In Lab and Real-World CO2 Output

Data shows that PHEVs release only 19% lower CO₂ than conventional petrol and diesel vehicles, based on research carried out by a advocacy group. This contrasts significantly with lab tests, which suggested a 75% reduction in pollution.

Researchers studied data from onboard energy use meters of eight hundred thousand cars sold in the EU between 2021 and 2023. The team discovered that real-world CO₂ emissions from PHEVs in 2023 were nearly five times higher than lab figures, up from 3.5 times in 2021.

“Real-world CO2 output are rising, while lab-reported figures are falling,” stated a lead researcher participating in the study. “This gap is widening and creates a serious problem. As a result, PHEVs pollute almost as much as gasoline vehicles.”

Primary Factors Driving the Emissions Gap

Researchers attributed most of the gap to overestimates of the “electric driving share” – the ratio of miles travelled in battery mode compared to total mileage. The team found that only 27% of travel was done in electric mode, while official estimates suggested over four-fifths.

Additionally, when operating in electric mode, pollution amounts were well above lab estimates. This happened because electric motors were insufficiently powerful enough to operate independently, resulting to engines burning gasoline for nearly one-third of the distance covered in electric mode.

Regulatory and Economic Consequences

Based on calculations, the underestimation of PHEV emissions enabled four major carmaker groups to avoid more than €5bn in penalties between 2021 and 2023, by falsely simplifying compliance with European Union average fleet CO₂ targets.

Furthermore, drivers of PHEVs would spend about €500 extra per year in running costs than is assumed under laboratory conditions.

“The bold statements that automakers often promote about their PHEV cars are obviously far from the mark,” commented a automotive analyst. “Buyers are being duped into thinking that by buying a PHEV, they are helping the environment and cutting costs. In reality, PHEVs are little better than standard petrol and diesel cars in terms of energy consumption, CO₂ production, and operating costs.”

Policy 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 standards. A proposed prohibition on new internal combustion cars in 2035 has faced heavy lobbying from the car industry and resistance from member states with large automotive industries.

Some high-level officials have proposed plug-in hybrids as a potential “flexibility” option to include in the regulation.

One external energy policy expert, who was unaffiliated with the study, described the analysis a “very useful addition” after a long period in which parts of the automotive sector claimed there was too little data to properly evaluate real-world CO2 output.

“The results show, without question, that the difference in lab and actual PHEV energy use and CO₂ emissions is much, much greater than for gasoline or conventional vehicles,” the expert said. “All regulatory changes concerning PHEVs should be implemented with utmost care and in the light of this data.”