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Plug-in hybrid electric vehicles emit nearly 5x greater global warming emissions than lab-reported figures show, as per a new analysis.

Growing Discrepancy Between Lab and Actual CO2 Output

Data reveals that PHEVs release only 19% less CO₂ than conventional gas and diesel vehicles, based on analysis conducted by a non-profit organization. That differs significantly with laboratory tests, which assumed a three-quarters decrease in emissions.

Analysts examined data from in-vehicle energy use monitors of eight hundred thousand vehicles registered in the EU from 2021 and 2023. The team discovered that actual CO₂ emissions from PHEVs in 2023 were 4.9 times higher than official estimates, increased from 3.5 times in 2021.

“Real-world CO2 output are increasing, while lab-reported figures are falling,” said a senior analyst participating in the report. “This gap is widening and poses a serious problem. As a result, PHEVs emit almost as much as petrol cars.”

Primary Reasons Behind the Emissions Gap

Researchers attributed the majority of the difference to inflated estimates of the “electric driving share” – the ratio of kilometers travelled in battery power compared to overall mileage. They determined that only a quarter of travel was completed in electric mode, while official estimates assumed over four-fifths.

Additionally, when operating in EV mode, emission levels were well above official estimates. That occurred because electric motors were not strong sufficient to function independently, leading to engines using fossil fuels for almost one-third of the travel completed in electric mode.

Policy and Financial Implications

According to calculations, the underestimation of PHEV CO2 output allowed several large automaker companies to avoid more than €5bn in penalties from 2021 and 2023, by artificially simplifying adherence with EU fleet-average CO₂ targets.

Additionally, drivers of PHEVs could spend approximately €500 more annually in running expenses than is estimated under lab conditions.

“The bold statements that manufacturers like to make about their plug-in hybrid vehicles are clearly far from the mark,” commented a automotive expert. “Consumers are being misled into believing that by purchasing a PHEV, they are benefiting the environment and saving costs. Actually, PHEVs are little improved than standard gas and diesel cars in terms of fuel consumption, CO₂ emissions, and running expenses.”

Policy Debate and Industry Pressure

Hybrid vehicles have lately been drawn again into political debates as carmakers have pressed the European Union to relax CO₂ standards. A planned ban on new combustion engine cars in 2035 has faced heavy lobbying from the car sector and resistance from EU countries with significant automotive manufacturing.

Some senior politicians have proposed plug-in hybrids as a potential “flexibility” solution to introduce in the regulation.

An external energy policy expert, who was not involved with the research, described the analysis a “highly valuable addition” after years in which segments of the automotive industry argued there was insufficient data to accurately assess actual emissions.

“The results demonstrate, without question, that the gap between lab and actual PHEV energy use and CO₂ output is much, much larger than for gasoline or conventional vehicles,” the expert said. “All policy adjustments concerning PHEVs should be implemented with extreme caution and considering that data.”