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Plug-in hybrid electric vehicles release nearly 5x more planet-heating pollution than lab-reported data show, as per a recent analysis.

Growing Gap In Official and Real-World CO2 Output

Data shows that PHEVs emit just one-fifth less CO₂ than traditional gas and diesel vehicles, according to analysis carried out by a non-profit organization. That contrasts significantly with laboratory tests, which assumed a 75% reduction in pollution.

Researchers examined data from onboard energy use monitors of 800,000 cars sold in Europe from 2021 and 2023. They discovered that actual CO₂ output from PHEVs in 2023 were 4.9 times higher than lab estimates, increased from three and a half times in 2021.

“Actual CO2 output are increasing, while lab-reported emissions are decreasing,” said a lead analyst involved in the study. “That discrepancy is widening and poses a significant issue. Consequently, PHEVs pollute nearly as much as petrol vehicles.”

Primary Reasons Behind the Emissions Gap

Analysts attributed most of the difference to overestimates of the “electric driving share” – the percentage of kilometers travelled in battery mode compared to overall distance. They determined that only 27% of travel was done in electric mode, while lab estimates assumed over four-fifths.

Even, when operating in EV mode, emission amounts were significantly higher than lab estimates. This happened because EV motors were insufficiently powerful enough to operate alone, leading to engines burning fossil fuels for nearly one-third of the travel covered in EV mode.

Policy and Financial Implications

According to calculations, the underestimation of PHEV emissions allowed several large automaker companies to avoid over €5bn in fines between 2021 and 2023, by artificially simplifying compliance with EU average fleet CO₂ targets.

Furthermore, drivers of PHEVs could spend approximately €500 extra annually in running expenses than is assumed under lab conditions.

“The bold statements that automakers often promote about their plug-in hybrid cars are obviously way off the truth,” commented a transport analyst. “Buyers are being misled into thinking that by purchasing a PHEV, they are benefiting the environment and saving money. In reality, PHEVs are only slightly improved than standard petrol and diesel cars in terms of energy consumption, CO₂ production, and running costs.”

Political Debate and Industry Pressure

Plug-in hybrid vehicles have lately been brought back into policy debates as carmakers have pressed the European Union to relax CO₂ targets. A planned ban on new combustion engine vehicles in 2035 has faced heavy pressure from the car industry and opposition from EU countries with large car manufacturing.

Several high-level officials have suggested plug-in hybrids as a possible “compromise” option to introduce in the legislation.

One external energy policy specialist, who was unaffiliated with the research, called the analysis a “highly valuable contribution” after a long period in which parts of the automotive industry claimed there was insufficient information to properly assess actual emissions.

“The results demonstrate, beyond any doubt, that the gap between official and actual PHEV energy use and CO₂ emissions is significantly greater than for petrol or diesel cars,” the expert stated. “All regulatory adjustments concerning PHEVs should be made with extreme caution and considering that evidence.”