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Plug-in hybrid cars produce nearly five times greater global warming emissions than official figures show, according to a recent analysis.

Widening Discrepancy Between Official and Real-World CO2 Output

Data shows that PHEVs release only one-fifth less CO₂ than conventional gas and diesel cars, according to analysis conducted by a advocacy group. That differs sharply with lab tests, which assumed a three-quarters reduction in emissions.

Researchers examined data from onboard fuel consumption meters of 800,000 cars sold in the EU from 2021 and 2023. The team found that real-world CO₂ emissions from PHEVs in 2023 were nearly five times greater than lab figures, increased from three and a half times in 2021.

“Real-world emissions are increasing, while lab-reported figures are decreasing,” said a lead analyst participating in the study. “That gap is widening and poses a serious issue. As a result, PHEVs emit almost as heavily as gasoline vehicles.”

Primary Reasons Behind the Emissions Gap

Researchers attributed the majority of the gap to inflated estimates of the “electric driving share” – the percentage of miles driven in electric mode compared to overall distance. The team found that only 27% of travel was completed in electric mode, whereas lab estimates suggested over four-fifths.

Even, when running in EV mode, emission amounts were well above lab estimates. This happened because electric motors were not strong sufficient to operate alone, resulting to engines using fossil fuels for nearly a third of the travel covered in electric mode.

Regulatory and Economic Implications

According to calculations, the underestimation of PHEV CO2 output enabled four major automaker companies to escape more than €5bn in fines from 2021 and 2023, by artificially easing adherence with European Union average fleet CO₂ targets.

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

“The bold claims that automakers often promote about their plug-in hybrid cars are obviously far from the truth,” stated a transport expert. “Buyers are being misled into thinking that by purchasing a PHEV, they are benefiting the environment and saving costs. Actually, PHEVs are only slightly better than standard gas and diesel cars in terms of energy consumption, CO₂ production, and operating expenses.”

Policy Debate and Industry Lobbying

Plug-in hybrid cars have recently been brought back into political debates as automakers have lobbied the European Union to relax CO₂ targets. A proposed prohibition on sales of new internal combustion cars in 2035 has faced intense lobbying from the automotive industry and resistance from member states with significant car industries.

Several senior politicians have proposed plug-in hybrids as a potential “flexibility” option to introduce in the legislation.

One external energy policy specialist, who was unaffiliated with the research, described the report a “highly valuable addition” after a long period in which parts of the car sector argued there was insufficient data to accurately evaluate real-world CO2 output.

“The results show, without question, that the difference between lab and actual PHEV fuel consumption and CO₂ output is significantly larger than for gasoline or conventional vehicles,” the expert said. “Any regulatory adjustments regarding PHEVs should be implemented with extreme caution and considering that evidence.”