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Plug-in hybrid cars release almost five times more planet-heating emissions than lab-reported figures show, according to a new report.

Growing Discrepancy Between Official and Actual CO2 Output

Statistics shows that PHEVs emit only 19% less CO₂ than traditional petrol and diesel vehicles, according to analysis conducted by a advocacy group. That contrasts significantly with lab estimates, which suggested a three-quarters decrease in emissions.

Analysts examined data from onboard energy use monitors of 800,000 cars registered in Europe between 2021 and 2023. They discovered that actual CO₂ output from PHEVs in 2023 were 4.9 times greater than official figures, up from 3.5 times in 2021.

“Actual emissions are rising, while official emissions are falling,” stated a senior researcher participating in the report. “This discrepancy is widening and creates a significant issue. As a result, PHEVs pollute nearly as much as gasoline cars.”

Primary Reasons Behind the Discrepancy

Analysts attributed most of the gap to overestimates of the “utility factor” – the ratio of kilometers driven in electric mode relative to overall distance. They found that just a quarter of travel was completed in electric mode, while lab assumptions assumed over four-fifths.

Additionally, when running in electric mode, emission amounts were significantly higher than lab estimates. This occurred because EV motors were not strong sufficient to operate alone, leading to combustion motors using gasoline for nearly a third of the distance completed in EV mode.

Regulatory and Economic Implications

According to calculations, the underestimation of PHEV CO2 output enabled several major automaker groups to escape more than €5bn in penalties from 2021 and 2023, by artificially easing compliance with European Union average fleet CO₂ standards.

Additionally, drivers of PHEVs could pay about €500 more per year in operating costs than is estimated under laboratory tests.

“The strong claims that automakers often promote about their PHEV cars are obviously way off the truth,” stated a transport expert. “Consumers are being misled into believing that by buying a PHEV, they are helping the environment and saving costs. Actually, PHEVs are only slightly better than regular petrol and diesel cars in terms of fuel use, CO₂ production, and operating expenses.”

Political Discussion and Automotive Lobbying

Plug-in hybrid vehicles have lately been brought back into political debates as carmakers have pressed the European Union to relax CO₂ standards. A proposed ban on new combustion engine cars in 2035 has faced heavy pressure from the automotive sector and resistance from member states with large car industries.

Several high-level politicians have suggested PHEVs as a possible “compromise” option to introduce in the regulation.

An independent energy policy specialist, who was not involved with the research, described the analysis a “highly valuable contribution” after years in which parts of the automotive industry argued there was too little data to accurately assess real-world CO2 output.

“The results demonstrate, beyond any doubt, that the difference in official and actual PHEV energy use and CO₂ emissions is much, much greater than for petrol or diesel cars,” the expert said. “Any policy changes concerning PHEVs should be implemented with utmost care and in the light of that data.”