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Plug-in hybrid cars emit nearly 5x more global warming emissions than official figures show, according to a recent analysis.

Widening Discrepancy In Lab and Actual Emissions

Data reveals that PHEVs release only 19% less CO₂ than traditional gas and diesel vehicles, based on analysis carried out by a non-profit group. This differs significantly with laboratory estimates, which assumed a three-quarters reduction in emissions.

Researchers examined data from in-vehicle fuel consumption meters of eight hundred thousand vehicles registered in the EU from 2021 and 2023. The team found that actual CO₂ output from PHEVs in 2023 were nearly five times greater than official figures, increased from 3.5 times in 2021.

“Actual CO2 output are increasing, while lab-reported emissions are falling,” stated a lead analyst involved in the report. “This discrepancy is widening and creates a serious issue. As a result, PHEVs pollute almost as much as gasoline cars.”

Key Factors Behind the Discrepancy

Analysts attributed the majority of the gap to overestimates of the “electric driving share” – the percentage of kilometers driven in battery power compared to overall distance. The team determined that only 27% of driving was done in electric mode, whereas official assumptions assumed over four-fifths.

Additionally, when operating in electric mode, pollution amounts were significantly higher than lab estimates. That happened because electric motors were not strong enough to function alone, resulting to engines using fossil fuels for nearly a third of the distance completed in electric mode.

Policy and Financial Implications

Based on calculations, the underestimation of PHEV CO2 output enabled four major automaker groups to escape more than €5bn in fines between 2021 and 2023, by falsely simplifying compliance with EU average fleet CO₂ targets.

Furthermore, drivers of PHEVs would pay approximately €500 extra per year in running expenses than is estimated under laboratory conditions.

“The strong claims that manufacturers often promote about their plug-in hybrid cars are clearly way off the mark,” stated a transport expert. “Buyers are being duped into believing that by buying a PHEV, they are helping the planet and cutting costs. In reality, PHEVs are little improved than regular petrol and diesel cars in terms of fuel consumption, CO₂ emissions, and operating costs.”

Policy Discussion and Industry Pressure

Hybrid vehicles have recently been brought back into political debates as carmakers have pressed the EU to relax CO₂ standards. A proposed prohibition on new combustion engine vehicles in 2035 has faced heavy pressure from the car industry and opposition from member states with significant automotive manufacturing.

Several senior politicians have proposed PHEVs as a possible “compromise” solution to include in the regulation.

One independent energy policy specialist, who was unaffiliated with the research, called the analysis a “very useful addition” after a long period in which parts of the automotive industry argued there was too little information to accurately assess actual emissions.

“The results demonstrate, without question, that the gap in lab and real-world PHEV fuel consumption and CO₂ output is much, much larger than for petrol or diesel vehicles,” the expert stated. “All policy changes regarding PHEVs should be implemented with utmost caution and in the light of that data.”