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Plug-in hybrid cars release nearly 5x greater planet-heating emissions than official data indicate, according to a new analysis.

Widening Discrepancy Between Lab and Real-World Emissions

Data reveals that PHEVs emit just one-fifth lower CO₂ than traditional petrol and diesel vehicles, according to research conducted by a advocacy organization. That differs significantly with laboratory estimates, which assumed a three-quarters reduction in emissions.

Researchers examined information from in-vehicle energy use meters of 800,000 vehicles registered in Europe from 2021 and 2023. They discovered that actual CO₂ output from PHEVs in 2023 were 4.9 times greater than official estimates, up from 3.5 times in 2021.

“Real-world emissions are increasing, while official emissions are falling,” stated a lead analyst involved in the report. “This discrepancy is widening and creates a significant problem. As a result, PHEVs pollute almost as much as petrol cars.”

Primary Reasons Driving the Discrepancy

Researchers linked most of the gap to overestimates of the “electric driving share” – the percentage of miles travelled in electric power relative to overall mileage. They found that only 27% of driving was done in electric mode, whereas lab assumptions assumed over four-fifths.

Additionally, when running in EV mode, pollution amounts were significantly higher than official estimates. This occurred because electric 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

Based on calculations, the underestimation of PHEV CO2 output allowed four large automaker companies to escape over €5bn in penalties between 2021 and 2023, by artificially easing adherence with European Union fleet-average CO₂ targets.

Additionally, owners of PHEVs would pay about €500 more per year in operating expenses than would be estimated under laboratory tests.

“The bold statements that manufacturers often promote about their PHEV cars are obviously way off the truth,” commented a automotive analyst. “Consumers are being duped into thinking that by purchasing a PHEV, they are benefiting the planet and saving costs. Actually, PHEVs are little better than standard petrol and diesel cars in terms of energy use, CO₂ production, and operating expenses.”

Political Discussion and Industry Lobbying

Plug-in hybrid cars have recently been brought again into policy discussions as carmakers have lobbied the European Union to weaken CO₂ standards. A proposed prohibition on sales of new combustion engine cars in 2035 has faced intense lobbying from the car sector and resistance from EU countries with significant car industries.

Some senior officials have suggested plug-in hybrids as a possible “flexibility” solution to introduce in the regulation.

An independent energy economics expert, who was not involved with the study, called the report a “highly valuable addition” after years in which parts of the car industry claimed there was insufficient data to accurately evaluate real-world emissions.

“The results demonstrate, without question, that the difference in official and real-world PHEV fuel consumption and CO₂ emissions is significantly greater than for gasoline or diesel vehicles,” they said. “Any regulatory changes concerning PHEVs should be implemented with extreme care and considering that data.”