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Plug-in hybrid cars emit almost five times greater planet-heating emissions than lab-reported data indicate, as per a recent analysis.

Growing Gap Between Lab and Real-World CO2 Output

Data shows that PHEVs release just 19% less CO₂ than traditional gas and diesel cars, according to research conducted by a non-profit organization. That differs sharply with laboratory estimates, which assumed a 75% reduction in emissions.

Analysts examined information from in-vehicle energy use monitors of 800,000 cars sold in Europe from 2021 and 2023. The team discovered that real-world CO₂ output from PHEVs in 2023 were 4.9 times higher than lab estimates, up from three and a half times in 2021.

“Real-world emissions are rising, while official emissions are decreasing,” stated a lead analyst involved in the report. “That discrepancy is widening and creates a significant issue. Consequently, PHEVs emit nearly as heavily as petrol cars.”

Primary Factors Driving the Emissions Gap

Analysts attributed the majority of the gap to inflated estimates of the “electric driving share” – the percentage of miles driven in battery power compared to total mileage. The team found that just 27% of driving was done in electric mode, while official assumptions suggested over four-fifths.

Additionally, when running in electric mode, pollution amounts were significantly higher than lab estimates. That happened because EV motors were not strong sufficient to operate independently, leading to engines using gasoline for almost one-third of the travel covered in EV mode.

Policy and Economic Consequences

According to calculations, the underestimation of PHEV CO2 output enabled several large carmaker groups to avoid over €5bn in penalties between 2021 and 2023, by falsely simplifying adherence with European Union fleet-average CO₂ targets.

Furthermore, owners of PHEVs would pay about €500 extra per year in running costs than is estimated under laboratory tests.

“The bold claims that manufacturers often promote about their PHEV cars are obviously far from the truth,” stated a transport analyst. “Consumers are being misled into thinking that by buying a PHEV, they are benefiting the environment and cutting costs. In reality, PHEVs are only slightly improved than regular petrol and diesel cars in terms of fuel use, CO₂ production, and operating costs.”

Political Debate and Automotive Pressure

Plug-in hybrid cars have recently been brought again into policy debates as carmakers have pressed the European Union to relax CO₂ standards. A proposed prohibition on sales of new combustion engine vehicles in 2035 has faced heavy lobbying from the car industry and resistance from member states with large automotive industries.

Some senior politicians have suggested plug-in hybrids as a possible “flexibility” solution to include in the legislation.

One external energy policy specialist, who was unaffiliated with the research, described the analysis a “highly valuable addition” after a long period in which parts of the car sector argued there was too little data to accurately assess actual emissions.

“These findings demonstrate, beyond any doubt, that the difference between lab and real-world PHEV fuel consumption and CO₂ output is much, much greater than for gasoline or diesel cars,” the expert stated. “All regulatory adjustments concerning PHEVs should be made with extreme care and in the light of this evidence.”