Once marketed as a climate-friendly compromise between petrol and electric power, plug-in hybrids are now shown to pollute far more than advertised, with actual emissions reaching 139g of CO₂ per kilometre versus 28g claimed.

Plug-in hybrids promised the best of both worlds: the efficiency of electric power for short urban trips of several dozen kilometres without emissions, combined with the range of a combustion engine for longer journeys. They appeal especially to customers hesitant to go fully electric, fearing insufficient range.

But the reality is far from ideal. Plug-in hybrids are often misused: many motorists, particularly those who receive them as company cars, rarely recharge the batteries. Carrying this extra weight increases petrol consumption and pollution, sometimes surpassing that of a conventional combustion engine.

A European study shows that CO2 emissions from plug-in hybrid vehicles were 3.5 times higher than manufacturers’ official figures. Yet the situation may be even worse: a new study by the European Environment Agency has sent shockwaves through the automotive sector.

The Brussels-based NGO Transport & Environment (T&E) reports that plug-in hybrids emit nearly five times more CO2 than official tests suggest. This gap has widened over the years (from 3.5 in 2021 to 4.9 in 2023) based on data from on-board fuel consumption meters.

"Contrary to manufacturers’ claims, plug-in hybrids are even worse for the climate than expected", says Bastien Gebel, head of decarbonisation in the automotive sector at T&E France.

28g CO2/km advertised, 139g in reality

Data on actual emissions was collected from on-board devices in 127,000 plug-in hybrids registered in 2023.

On average, the cars tested emitted 139g of CO2 per kilometre, while official WLTP (Worldwide Harmonised Light Vehicle Test Procedure) tests claim just 28g CO2/km. The gap exists because the standard assumes plug-in hybrids will run in electric mode over 80% of the time, whereas in practice drivers use electric mode for only around 26% of their journeys.

Improper use

These so-called “green cars” are therefore far less beneficial than expected because drivers often do not use them as intended. If hybrid drivers relied more on electric mode, CO2 emissions would drop considerably.

However, the hybrid market is largely dominated by companies aiming to green their fleets who then equip employees with these vehicles, often also providing fuel cards. Many employees lack a charging point at home, which means hybrids are rarely driven in electric mode. As a result, the technology is misused, and plug-in hybrids can have a worse environmental impact than fully electric vehicles.

This widespread misuse misleads consumers about the true emissions and fuel consumption of plug-in hybrids, while allowing manufacturers to advertise them as clean vehicles and artificially lower their CO2 targets.