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Plug-in hybrid cars emit almost 5x more global warming emissions than lab-reported data show, according to a recent analysis.

Growing Gap In Lab and Real-World CO2 Output

Data shows that PHEVs emit only one-fifth lower CO₂ than traditional petrol and diesel vehicles, based on analysis conducted by a non-profit organization. This differs sharply with lab estimates, which suggested a 75% decrease in pollution.

Analysts studied data from in-vehicle energy use meters of eight hundred thousand vehicles sold in the EU from 2021 and 2023. The team discovered that actual CO₂ output from PHEVs in 2023 were nearly five times higher than official figures, increased from 3.5 times in 2021.

“Actual emissions are increasing, while official figures are decreasing,” said a senior analyst participating in the study. “That discrepancy is widening and creates a serious problem. As a result, PHEVs pollute almost as much as gasoline cars.”

Primary Reasons Behind the Discrepancy

Analysts attributed most of the difference to overestimates of the “electric driving share” – the percentage of kilometers driven in battery power relative to overall mileage. The team determined that only 27% of travel was done in electric mode, whereas official assumptions suggested 84%.

Even, when operating in EV mode, pollution levels were well above official estimates. That happened because EV motors were not strong sufficient to function alone, resulting to combustion motors using fossil fuels for nearly one-third of the distance covered in EV mode.

Policy and Financial Implications

Based on estimates, the underestimation of PHEV CO2 output enabled four large automaker companies to avoid more than €5bn in penalties between 2021 and 2023, by artificially simplifying compliance with EU fleet-average CO₂ standards.

Furthermore, drivers of PHEVs would pay approximately €500 extra annually in running costs than would be assumed under lab tests.

“The strong claims that manufacturers often promote about their PHEV vehicles are obviously far from the truth,” stated a transport analyst. “Buyers are being duped into believing that by buying a PHEV, they are helping the planet and saving money. In reality, PHEVs are only slightly better than standard petrol and diesel vehicles in terms of fuel consumption, CO₂ production, and running expenses.”

Policy Debate and Automotive Lobbying

Plug-in hybrid cars have lately been drawn back into political discussions as automakers have lobbied the European Union to relax CO₂ standards. A proposed ban on new combustion engine vehicles in 2035 has faced heavy lobbying from the car sector and opposition from member states with large automotive manufacturing.

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

An external energy economics expert, who was unaffiliated with the study, called the analysis a “very useful contribution” after years in which segments of the automotive sector argued there was too little data to accurately assess actual CO2 output.

“The results demonstrate, beyond any doubt, that the gap between lab and real-world PHEV fuel consumption and CO₂ output is much, much greater than for gasoline or conventional vehicles,” they said. “All policy changes regarding PHEVs should be implemented with extreme caution and considering that data.”