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Plug-in hybrid electric vehicles release almost 5x more planet-heating emissions than official data indicate, according to a new analysis.

Growing Discrepancy Between Official and Real-World Emissions

Data reveals that PHEVs release only one-fifth lower CO₂ than traditional gas and diesel vehicles, based on research carried out by a advocacy organization. That contrasts significantly with laboratory estimates, which assumed a three-quarters reduction in emissions.

Researchers examined data from in-vehicle energy use monitors of 800,000 cars sold in Europe between 2021 and 2023. They discovered that actual CO₂ emissions from PHEVs in 2023 were 4.9 times greater than official figures, up from 3.5 times in 2021.

“Actual CO2 output are rising, while official emissions are falling,” said a lead researcher involved in the report. “This gap is growing and poses a significant problem. As a result, PHEVs pollute almost as much as gasoline vehicles.”

Key Factors Behind the Discrepancy

Analysts attributed most of the gap to inflated estimates of the “utility factor” – the ratio of miles travelled in battery mode compared to total distance. The team found that just 27% of travel was done in EV mode, while official estimates assumed 84%.

Even, when operating in EV mode, emission levels were significantly higher than lab projections. That happened because electric motors were not strong enough to operate independently, resulting to combustion motors burning fossil fuels for nearly one-third of the distance covered in EV mode.

Policy and Financial Implications

According to estimates, the underestimation of PHEV emissions enabled several major automaker groups to escape more than €5bn in fines from 2021 and 2023, by falsely easing compliance with EU average fleet CO₂ targets.

Furthermore, drivers of PHEVs could spend about €500 extra per year in running costs than is assumed under laboratory conditions.

“The bold statements that manufacturers like to make about their plug-in hybrid cars are obviously far from the truth,” stated a automotive expert. “Consumers are being duped into thinking that by buying a PHEV, they are benefiting the environment and cutting costs. Actually, PHEVs are only slightly improved than regular gas and diesel cars in terms of fuel use, CO₂ production, and running costs.”

Political Debate and Industry Lobbying

Plug-in hybrid cars have lately been drawn back into policy discussions as carmakers have pressed the European Union to relax CO₂ targets. A planned prohibition on new internal combustion vehicles in 2035 has faced heavy lobbying from the automotive sector and opposition from member states with large car industries.

Some high-level officials have proposed plug-in hybrids as a possible “flexibility” solution to include in the regulation.

An independent energy economics expert, who was not involved with the study, called the report a “highly valuable contribution” after a long period in which parts of the car industry argued there was too little data to accurately assess real-world CO2 output.

“The results demonstrate, without question, that the gap in lab and real-world PHEV energy use and CO₂ output is much, much larger than for petrol or diesel cars,” the expert said. “All regulatory adjustments regarding PHEVs should be made with utmost caution and considering that evidence.”