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Plug-in hybrid cars produce almost 5x more global warming pollution than official data indicate, according to a new report.

Growing Discrepancy Between Official and Actual CO2 Output

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

Researchers examined data from onboard fuel consumption monitors of 800,000 cars registered in the EU between 2021 and 2023. They found that real-world CO₂ output from PHEVs in 2023 were 4.9 times greater than official estimates, up from 3.5 times in 2021.

“Actual emissions are increasing, while lab-reported figures are falling,” said a lead researcher participating in the study. “That gap is widening and poses a serious issue. Consequently, PHEVs pollute almost as heavily as petrol vehicles.”

Key Factors Behind the Emissions Gap

Analysts attributed the majority of the difference to overestimates of the “utility factor” – the ratio of miles driven in battery power compared to overall mileage. They found that only 27% of driving was done in EV mode, while lab assumptions assumed over four-fifths.

Additionally, when operating in electric mode, emission amounts were significantly higher than official estimates. That happened because electric motors were not strong enough to operate independently, resulting to engines burning fossil fuels for nearly a third of the distance covered in electric mode.

Regulatory and Economic Consequences

Based on estimates, the underestimation of PHEV CO2 output allowed four large automaker groups to escape more than €5bn in fines from 2021 and 2023, by artificially easing adherence with EU fleet-average CO₂ targets.

Additionally, drivers of PHEVs would spend approximately €500 more per year in operating expenses than is estimated under lab conditions.

“The bold claims that manufacturers often promote about their plug-in hybrid cars are clearly way off the mark,” commented a transport expert. “Buyers are being duped into believing that by purchasing a PHEV, they are helping the planet and saving money. In reality, PHEVs are little improved than regular gas and diesel cars in terms of energy use, CO₂ emissions, and running costs.”

Policy Debate and Industry Lobbying

Hybrid vehicles have lately been drawn again into policy debates as automakers have lobbied the European Union to weaken CO₂ standards. A proposed ban on sales of new internal combustion vehicles in 2035 has faced intense lobbying from the automotive industry and opposition from member states with large automotive industries.

Some high-level officials have proposed PHEVs as a possible “flexibility” solution to introduce in the regulation.

One external energy policy specialist, who was not involved with the study, called the analysis a “very useful contribution” after a long period in which parts of the automotive sector claimed there was too little information to accurately assess real-world CO2 output.

“These findings show, beyond any doubt, that the difference between official and actual PHEV energy use and CO₂ output is significantly greater than for petrol or diesel cars,” they said. “Any policy adjustments regarding PHEVs should be made with utmost care and considering that evidence.”