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Plug-in hybrid electric vehicles emit almost five times more global warming emissions than official figures show, according to a new analysis.

Growing Discrepancy Between Lab and Real-World CO2 Output

Data shows that PHEVs emit just one-fifth lower CO₂ than traditional petrol and diesel vehicles, according to analysis conducted by a advocacy organization. This differs sharply with laboratory estimates, which suggested a 75% decrease in emissions.

Analysts examined data from onboard energy use meters of eight hundred thousand cars registered in the EU between 2021 and 2023. The team discovered that actual CO₂ emissions from PHEVs in 2023 were nearly five times greater than official estimates, up from 3.5 times in 2021.

“Real-world CO2 output are rising, while lab-reported figures are falling,” said a senior analyst participating in the report. “That discrepancy is widening and poses a serious problem. Consequently, PHEVs pollute nearly as much as gasoline vehicles.”

Primary Reasons Driving the Emissions Gap

Researchers linked the majority of the difference to overestimates of the “utility factor” – the ratio of kilometers travelled in battery power compared to total mileage. They found that just 27% of driving was completed in EV mode, whereas official estimates suggested over four-fifths.

Even, when running in electric mode, emission levels were well above lab estimates. This happened because EV motors were insufficiently powerful sufficient to function alone, leading to engines burning fossil fuels for nearly one-third of the travel covered in electric mode.

Policy and Financial Consequences

According to calculations, the underestimation of PHEV emissions enabled four large automaker companies to escape more than €5bn in fines from 2021 and 2023, by falsely easing compliance with EU fleet-average CO₂ targets.

Additionally, owners of PHEVs could pay about €500 extra per year in running costs than would be estimated under lab tests.

“The strong statements that manufacturers often promote about their PHEV vehicles are obviously far from the mark,” commented a transport analyst. “Buyers are being duped into believing that by purchasing a PHEV, they are helping the planet and cutting costs. In reality, PHEVs are only slightly better than standard gas and diesel cars in terms of energy consumption, CO₂ emissions, and running costs.”

Political Discussion and Automotive Pressure

Hybrid vehicles have recently been brought back into policy debates as carmakers have pressed the EU to weaken CO₂ targets. A planned prohibition on sales of new internal combustion vehicles in 2035 has faced intense lobbying from the car industry and resistance from EU countries with large car industries.

Several senior politicians have proposed plug-in hybrids as a possible “compromise” solution to include in the regulation.

An independent energy economics expert, who was unaffiliated with the research, called the report a “highly valuable contribution” after a long period in which segments of the automotive industry argued there was insufficient data to accurately assess actual CO2 output.

“The results demonstrate, beyond any doubt, that the difference in lab and actual PHEV energy use and CO₂ emissions is significantly larger than for petrol or conventional vehicles,” they said. “All regulatory adjustments concerning PHEVs should be made with extreme care and considering that evidence.”