Plug-in hybrid electric vehicles (PHEVs) release nearly five times more greenhouse gas emissions than reported statistics suggest. I found a report detailing this issue.

These vehicles can operate on electric batteries as well as internal combustion engines and have been promoted by European manufacturers as a means to travel longer distances while lowering emissions—offering an alternative to fully electric cars.

Research indicates that PHEVs emit just 19% less CO₂. An analysis from the nonprofit organization Transport and Environment was released on Thursday, showing laboratory tests estimated 75% less pollution.

Researchers examined data from fuel consumption meters in 800,000 vehicles registered in Europe between 2021 and 2023, discovering that the real carbon dioxide emissions from PHEVs in 2023 were 4.9 times greater than those from standardized lab tests, an increase from 3.5 times in 2021.

“While official emissions are declining, actual emissions are on the rise,” remarked Sofia Navas Goelke, a researcher at the Institute for Transport and Environment and co-author of the report. “This widening gap is becoming a significant issue. Consequently, PHEVs are now polluting nearly as much as traditional petrol vehicles.”

The researchers identified that much of this disparity stems from an overestimation of the “utility factor” (the proportion of miles driven in electric mode compared to total miles), finding that only 27% of driving was done in electric mode, versus the official estimate of 84%. The analysis noted that the European Commission proposed two amendments to the utility coefficient ratio, which lessened the gap but didn’t eliminate it entirely.

Even when operating in electric mode, pollution levels were found to be significantly higher than official figures suggest. Researchers indicated this was due to the electric motor being insufficient for sole operation, with the engine burning fossil fuels for almost one-third of the distance traveled in electric mode.

Patrick Plotz, head of energy economics at the Fraunhofer Institute for System Innovation, who did not participate in the study, described it as a “very useful contribution” to ongoing discussions, as some in the automotive industry have claimed there’s insufficient data to accurately gauge real emissions.

“Without a doubt, the disparity between official and actual fuel consumption and CO₂ emissions for PHEVs is substantial,” Plotz remarked. “Their emissions are much higher than those of gasoline or diesel cars,” referring to the study on the topic. “Any policy adjustments regarding PHEVs should be thoughtfully considered in the context of this data.”

Hybrid vehicles have re-entered political discourse as automakers urge the EU to ease carbon emission targets. The push to ban new internal combustion engine vehicles by 2035 is facing strong lobbying from the auto sector, along with resistance from member states with significant automotive industries.

“There should be no significant reductions in 2035,” stated German Chancellor Friedrich Merz following a summit with Germany’s struggling automotive sector, committing to “do everything possible in 2035.” Other senior German leaders have cited plug-in hybrids as an example of “flexibility” that could be integrated into the legislation.

Researchers calculated that the undervaluation of PHEV emissions artificially facilitated compliance with the EU’s average vehicle CO2 regulations, enabling four major car manufacturers to evade over €5 billion (around £4.3 billion) in fines between 2021 and 2023. The study indicated that PHEV drivers are likely to incur approximately €500 more in annual running costs than expectations based on lab tests.

“The exaggerated claims made by manufacturers regarding their plug-in hybrid vehicles are clearly misleading,” observed Colin Walker, a transportation analyst at Energy and Climate Intelligence.

“Consumers are misled into thinking that by choosing a PHEV, they are aiding the environment and saving money,” he pointed out. “In reality, PHEVs are only marginally more efficient than regular petrol and diesel vehicles concerning fuel and CO₂ consumption, resulting in higher operation costs.”