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Plug-in hybrid cars emit almost 5x more planet-heating emissions than official data indicate, according to a new report.

Widening Gap Between Official and Real-World CO2 Output

Data shows that PHEVs release just 19% less CO₂ than traditional gas and diesel cars, based on analysis conducted by a non-profit group. That differs sharply with lab tests, which suggested a three-quarters decrease in pollution.

Analysts studied data from in-vehicle energy use monitors of 800,000 cars registered in Europe between 2021 and 2023. They discovered that real-world CO₂ emissions from PHEVs in 2023 were nearly five times higher than official estimates, up from 3.5 times in 2021.

“Actual CO2 output are rising, while official figures are decreasing,” stated a lead researcher participating in the report. “That discrepancy is widening and creates a significant issue. As a result, PHEVs pollute nearly as heavily as petrol vehicles.”

Key Factors Behind the Emissions Gap

Analysts attributed most of the difference to inflated estimates of the “electric driving share” – the ratio of kilometers driven in electric mode relative to total distance. The team determined that just a quarter of travel was completed in electric mode, whereas official estimates suggested over four-fifths.

Even, when operating in electric mode, emission levels were significantly higher than lab projections. That happened because EV motors were not strong enough to operate independently, leading to engines burning fossil fuels for almost a third of the travel completed in EV mode.

Regulatory and Financial Consequences

According to calculations, the lowballing of PHEV emissions allowed several major carmaker groups to avoid over €5bn in fines between 2021 and 2023, by falsely simplifying adherence with European Union average fleet CO₂ standards.

Furthermore, owners of PHEVs could pay about €500 extra per year in running expenses than is assumed under lab conditions.

“The bold claims that manufacturers often promote about their PHEV cars are clearly far from the mark,” commented a automotive expert. “Consumers are being misled into believing that by buying a PHEV, they are benefiting the environment and saving costs. In reality, PHEVs are only slightly improved than regular gas and diesel vehicles in terms of energy consumption, CO₂ emissions, and running costs.”

Political Debate and Automotive Lobbying

Hybrid vehicles have recently been drawn again into policy debates as automakers have lobbied the European Union to relax CO₂ targets. A proposed prohibition on sales of new combustion engine cars in 2035 has faced intense lobbying from the automotive sector and resistance from member states with significant automotive manufacturing.

Some high-level politicians have proposed plug-in hybrids as a possible “flexibility” option to include in the legislation.

An external energy policy expert, who was not involved with the research, described the report a “highly valuable contribution” after a long period in which parts of the car industry claimed there was insufficient information to accurately evaluate actual emissions.

“These findings show, beyond any doubt, that the difference in lab and actual PHEV energy use and CO₂ output is significantly larger than for gasoline or conventional vehicles,” the expert said. “All policy changes regarding PHEVs should be made with extreme caution and in the light of this evidence.”