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Plug-in hybrid cars produce almost 5x more planet-heating emissions than official data indicate, according to a new report.

Growing Discrepancy Between Lab and Real-World CO2 Output

Statistics reveals that PHEVs emit just 19% lower CO₂ than traditional petrol and diesel cars, based on analysis carried out by a non-profit group. That contrasts significantly with lab tests, which suggested a 75% decrease in pollution.

Researchers studied information from in-vehicle energy use meters of 800,000 cars sold in the EU from 2021 and 2023. The team found that real-world CO₂ emissions from PHEVs in 2023 were 4.9 times higher than lab figures, increased from three and a half times in 2021.

“Real-world CO2 output are rising, while lab-reported figures are falling,” said a lead analyst participating in the report. “This gap is growing and creates a serious issue. Consequently, PHEVs pollute nearly as much as gasoline vehicles.”

Primary Factors Behind the Discrepancy

Analysts attributed most of the gap to overestimates of the “utility factor” – the ratio of kilometers travelled in electric mode relative to overall distance. The team determined that only a quarter of driving was done in EV mode, whereas lab estimates suggested 84%.

Additionally, when running in EV mode, emission levels were well above lab estimates. That happened because EV motors were insufficiently powerful enough to operate independently, resulting to engines using gasoline for nearly a third of the distance covered in EV mode.

Regulatory and Economic Consequences

Based on calculations, the lowballing of PHEV CO2 output enabled four large automaker groups to avoid more than €5bn in penalties from 2021 and 2023, by artificially easing compliance with European Union average fleet CO₂ standards.

Furthermore, owners of PHEVs could spend approximately €500 more annually in running expenses than is assumed under lab conditions.

“The strong claims that manufacturers like to make about their PHEV vehicles are obviously way off the truth,” stated a automotive expert. “Buyers are being duped into believing that by buying a PHEV, they are benefiting the environment and saving money. In reality, PHEVs are only slightly improved than regular petrol and diesel cars in terms of energy consumption, CO₂ production, and running costs.”

Political Debate and Industry Pressure

Plug-in hybrid vehicles have lately been drawn again into policy discussions as carmakers have pressed the European Union to weaken CO₂ standards. A planned prohibition on new combustion engine vehicles in 2035 has faced heavy pressure from the automotive industry and resistance from member states with significant automotive industries.

Some senior politicians have suggested plug-in hybrids as a possible “compromise” option to include in the regulation.

An external energy economics expert, who was not involved with the research, called the report a “highly valuable contribution” after years in which parts of the automotive sector argued there was too little data to properly assess actual CO2 output.

“These findings show, without question, that the difference in lab and real-world PHEV fuel consumption and CO₂ output is much, much larger than for gasoline or diesel cars,” they said. “Any policy changes regarding PHEVs should be made with utmost caution and in the light of this evidence.”