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Plug-in hybrid electric vehicles emit almost 5x more planet-heating pollution than official figures indicate, according to a recent analysis.

Growing Discrepancy Between Official and Actual CO2 Output

Data shows that PHEVs release only 19% lower CO₂ than traditional gas and diesel vehicles, according to analysis conducted by a advocacy group. That differs sharply with laboratory tests, which suggested a three-quarters reduction in pollution.

Researchers examined data from in-vehicle energy use monitors of eight hundred thousand cars registered in the EU between 2021 and 2023. They discovered that real-world CO₂ output from PHEVs in 2023 were 4.9 times higher than official estimates, increased from three and a half times in 2021.

“Real-world CO2 output are rising, while lab-reported emissions are decreasing,” said a senior analyst involved in the study. “That gap is growing and creates a significant issue. Consequently, PHEVs emit nearly as heavily as petrol vehicles.”

Primary Factors Behind the Emissions Gap

Researchers linked the majority of the gap to inflated estimates of the “electric driving share” – the percentage of kilometers travelled in electric power compared to overall distance. The team determined that only 27% of driving was completed in electric mode, whereas lab assumptions assumed 84%.

Additionally, when operating in EV mode, pollution levels were well above lab estimates. This happened because electric motors were not strong sufficient to operate independently, leading to combustion motors using fossil fuels for almost a third of the travel completed in EV mode.

Regulatory and Economic Consequences

According to estimates, the lowballing of PHEV CO2 output enabled several major carmaker companies to avoid more than €5bn in fines from 2021 and 2023, by artificially simplifying compliance with EU average fleet CO₂ standards.

Additionally, drivers of PHEVs could spend about €500 more annually in operating costs than would be assumed under lab tests.

“The strong statements that manufacturers often promote about their plug-in hybrid cars are clearly far from the truth,” commented a automotive analyst. “Consumers are being duped into thinking that by purchasing a PHEV, they are helping the environment and cutting money. In reality, PHEVs are only slightly better than standard petrol and diesel vehicles in terms of energy use, CO₂ emissions, and operating expenses.”

Policy Debate and Industry Pressure

Hybrid vehicles have recently been brought back into policy debates as automakers have pressed the European Union to relax CO₂ targets. A proposed prohibition on sales of new combustion engine vehicles in 2035 has faced heavy lobbying from the car sector and resistance from EU countries with large automotive industries.

Some high-level officials have proposed PHEVs as a potential “compromise” option to introduce in the regulation.

One external energy policy expert, who was unaffiliated with the research, called the analysis a “very useful contribution” after a long period in which segments of the automotive industry argued there was too little data to properly evaluate actual CO2 output.

“These findings show, beyond any doubt, that the gap between official and real-world PHEV fuel consumption and CO₂ output is much, much larger than for petrol or conventional cars,” they stated. “Any policy changes concerning PHEVs should be implemented with utmost caution and considering that data.”