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PHEVs release almost 5x greater global warming emissions than lab-reported data indicate, according to a recent analysis.

Widening Gap Between Official and Actual CO2 Output

Data reveals that PHEVs release just 19% lower CO₂ than traditional gas and diesel vehicles, according to research conducted by a advocacy organization. That differs significantly with laboratory tests, which assumed a three-quarters reduction in emissions.

Researchers examined data from in-vehicle energy use monitors of 800,000 vehicles registered in the EU between 2021 and 2023. The team discovered that actual CO₂ output from PHEVs in 2023 were 4.9 times higher than official estimates, up from 3.5 times in 2021.

“Actual CO2 output are increasing, while lab-reported figures are falling,” stated a lead researcher participating in the study. “This gap is growing and creates a significant problem. As a result, PHEVs pollute nearly as much as petrol cars.”

Key Reasons Behind the Emissions Gap

Researchers linked most of the gap to inflated estimates of the “electric driving share” – the percentage of kilometers driven in battery power compared to total mileage. They determined that only 27% of driving was done in EV mode, whereas official assumptions assumed 84%.

Even, when running in electric mode, pollution levels were well above official estimates. This happened because electric motors were insufficiently powerful sufficient to operate independently, leading to engines burning fossil fuels for almost a third of the distance completed in electric mode.

Regulatory and Economic Consequences

Based on estimates, the lowballing of PHEV CO2 output enabled four large carmaker groups to avoid over €5bn in fines between 2021 and 2023, by artificially simplifying compliance with European Union fleet-average CO₂ standards.

Additionally, owners of PHEVs could spend approximately €500 more annually in operating costs than would be assumed under laboratory conditions.

“The strong claims that manufacturers often promote about their plug-in hybrid vehicles are clearly far from the mark,” commented a automotive expert. “Consumers are being duped into thinking that by purchasing a PHEV, they are helping the environment and saving money. Actually, PHEVs are little better than standard gas and diesel vehicles in terms of fuel use, CO₂ production, and operating expenses.”

Policy Discussion and Automotive Pressure

Plug-in hybrid vehicles have lately been brought again into policy discussions as automakers have lobbied the EU to weaken CO₂ targets. A planned ban on sales of new internal combustion cars in 2035 has faced heavy pressure from the automotive sector and resistance from member states with large car industries.

Some senior officials have suggested PHEVs as a possible “flexibility” solution to include in the regulation.

One external energy economics expert, who was unaffiliated with the research, called the analysis a “very useful addition” after years in which segments of the automotive sector argued there was insufficient information to properly assess real-world CO2 output.

“These findings demonstrate, without question, that the difference in official and real-world PHEV fuel consumption and CO₂ output is significantly larger than for petrol or conventional cars,” they said. “All regulatory adjustments concerning PHEVs should be implemented with extreme care and in the light of this data.”