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Plug-in hybrid electric vehicles produce almost five times greater global warming pollution than official figures show, according to a new analysis.

Widening Gap Between Lab and Real-World CO2 Output

Statistics shows that PHEVs release just 19% less CO₂ than conventional petrol and diesel cars, according to research conducted by a advocacy group. This differs significantly with laboratory estimates, which suggested a three-quarters decrease in emissions.

Researchers studied information from in-vehicle fuel consumption monitors of 800,000 vehicles registered in the EU from 2021 and 2023. They found that actual CO₂ output from PHEVs in 2023 were nearly five times higher than official figures, up from three and a half times in 2021.

“Real-world CO2 output are increasing, while lab-reported emissions are decreasing,” said a lead analyst involved in the report. “That gap is widening and creates a significant problem. As a result, PHEVs emit nearly as heavily as petrol cars.”

Primary Factors Driving the Discrepancy

Analysts linked most of the difference to inflated estimates of the “utility factor” – the percentage of kilometers travelled in battery power relative to overall distance. They determined that just 27% of travel was done in EV mode, whereas lab assumptions suggested 84%.

Additionally, when running in EV mode, pollution levels were well above lab estimates. That occurred because electric motors were insufficiently powerful sufficient to operate alone, leading to combustion motors burning fossil fuels for nearly one-third of the travel covered in electric mode.

Policy and Financial Consequences

According to calculations, the lowballing of PHEV CO2 output enabled several large carmaker companies to avoid over €5bn in penalties between 2021 and 2023, by falsely simplifying compliance with European Union average fleet CO₂ targets.

Additionally, owners of PHEVs would spend approximately €500 more per year in running costs than is assumed under lab tests.

“The bold claims that manufacturers often promote about their plug-in hybrid vehicles are clearly far from the mark,” commented a transport expert. “Buyers are being duped into believing that by buying a PHEV, they are benefiting the planet and cutting costs. In reality, PHEVs are little improved than standard petrol and diesel vehicles in terms of fuel consumption, CO₂ production, and running costs.”

Policy Discussion and Industry Lobbying

Hybrid vehicles have recently been brought again into policy debates as automakers have lobbied the EU to weaken CO₂ targets. A proposed ban on sales of new combustion engine cars in 2035 has faced heavy lobbying from the automotive industry and opposition from member states with significant automotive industries.

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

An independent energy policy expert, who was not involved with the research, called the report a “highly valuable addition” after a long period in which parts of the car sector argued there was too little information to properly assess real-world CO2 output.

“These findings demonstrate, without question, that the gap between official and actual PHEV fuel consumption and CO₂ output is much, much larger than for petrol or conventional vehicles,” the expert stated. “All policy changes concerning PHEVs should be made with utmost caution and considering this evidence.”