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Plug-in hybrid cars emit almost 5x greater global warming pollution than official data indicate, according to a new report.

Widening Discrepancy Between Lab and Actual CO2 Output

Data shows that PHEVs emit just one-fifth less CO₂ than conventional gas and diesel vehicles, according to analysis carried out by a advocacy group. That differs significantly with laboratory estimates, which assumed a 75% decrease in emissions.

Researchers examined data from in-vehicle energy use monitors of eight hundred thousand vehicles registered in Europe between 2021 and 2023. The team found that real-world CO₂ emissions from PHEVs in 2023 were 4.9 times greater than lab estimates, increased from three and a half times in 2021.

“Actual emissions are increasing, while lab-reported emissions are decreasing,” stated a lead researcher participating in the study. “This gap is widening and creates a serious issue. As a result, PHEVs pollute nearly as heavily as gasoline cars.”

Key Reasons Behind the Discrepancy

Researchers attributed most of the difference to overestimates of the “electric driving share” – the ratio of miles travelled in electric mode compared to total distance. They determined that only a quarter of travel was done in EV mode, while lab assumptions assumed 84%.

Even, when operating in EV mode, emission levels were significantly higher than official estimates. This occurred because electric motors were not strong sufficient to operate independently, resulting to engines using fossil fuels for nearly a third of the distance covered in EV mode.

Policy and Financial Implications

According to estimates, the underestimation of PHEV emissions enabled four large carmaker groups to avoid more than €5bn in penalties between 2021 and 2023, by artificially easing adherence with EU average fleet CO₂ targets.

Additionally, owners of PHEVs could pay about €500 more annually in operating expenses than would be estimated under lab tests.

“The strong statements that manufacturers often promote about their plug-in hybrid cars are clearly way off the truth,” commented a transport expert. “Consumers are being duped into thinking that by purchasing a PHEV, they are helping the environment and saving money. Actually, PHEVs are only slightly better than regular gas and diesel cars in terms of energy use, CO₂ production, and running costs.”

Political Debate and Automotive Lobbying

Hybrid vehicles have lately been drawn back into policy discussions as automakers have lobbied the European Union to weaken CO₂ standards. A proposed ban on sales of new combustion engine vehicles in 2035 has faced intense pressure from the automotive sector and opposition from member states with significant automotive industries.

Some high-level officials have suggested PHEVs as a possible “flexibility” option to include in the legislation.

An independent energy policy specialist, who was not involved with the study, called the analysis a “highly valuable addition” after a long period in which parts of the automotive sector argued there was insufficient data to properly assess actual CO2 output.

“The results show, without question, that the gap between lab and real-world PHEV fuel consumption and CO₂ output is significantly greater than for petrol or conventional cars,” the expert said. “All regulatory adjustments concerning PHEVs should be made with extreme care and in the light of that data.”