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

Widening Gap Between Official and Real-World CO2 Output

Data reveals that PHEVs emit only 19% lower CO₂ than conventional petrol and diesel vehicles, based on analysis conducted by a advocacy group. This contrasts significantly with lab estimates, which assumed a 75% reduction in pollution.

Researchers examined information from onboard energy use monitors of eight hundred thousand cars registered in the EU between 2021 and 2023. The team found that real-world CO₂ output from PHEVs in 2023 were 4.9 times higher than lab estimates, increased from 3.5 times in 2021.

“Actual CO2 output are increasing, while lab-reported emissions are decreasing,” stated a senior analyst involved in the report. “This discrepancy is widening and poses a serious issue. As a result, PHEVs emit almost as much as petrol vehicles.”

Key Reasons Driving the Discrepancy

Analysts attributed the majority of the gap to inflated estimates of the “utility factor” – the ratio of kilometers travelled in battery power compared to overall mileage. They determined that only a quarter of travel was done in EV mode, while lab assumptions suggested 84%.

Additionally, when operating in EV mode, emission amounts were well above official estimates. This occurred because electric motors were not strong sufficient to function alone, leading to combustion motors burning fossil fuels for almost one-third of the travel covered in electric mode.

Policy and Economic Implications

Based on calculations, the lowballing of PHEV emissions allowed several large automaker companies to avoid more than €5bn in penalties between 2021 and 2023, by falsely easing adherence with European Union average fleet CO₂ targets.

Furthermore, owners of PHEVs could spend approximately €500 more per year in running costs than is assumed under laboratory conditions.

“The bold claims that manufacturers like to make about their PHEV vehicles are clearly way off the truth,” stated a automotive expert. “Buyers are being duped into thinking that by buying a PHEV, they are benefiting the planet and cutting money. In reality, PHEVs are little improved than regular petrol and diesel vehicles in terms of energy consumption, CO₂ production, and running costs.”

Policy Discussion and Automotive Pressure

Plug-in hybrid cars have recently been brought again into policy discussions as carmakers have pressed the European Union to relax CO₂ targets. A proposed ban on sales of new combustion engine cars in 2035 has faced heavy pressure from the automotive sector and opposition from EU countries with significant automotive industries.

Some high-level politicians have proposed plug-in hybrids as a possible “flexibility” solution to introduce in the regulation.

One independent energy policy expert, who was not involved with the research, described the report a “highly valuable addition” after a long period in which parts of the automotive sector claimed there was insufficient information to accurately evaluate actual emissions.

“These findings demonstrate, beyond any doubt, that the gap between lab and actual PHEV fuel consumption and CO₂ output is much, much greater than for gasoline or diesel vehicles,” they said. “Any regulatory adjustments regarding PHEVs should be made with extreme care and in the light of this data.”