Plug-in hybrids pollute 5 times more than announced: the study which overwhelms manufacturers

9% of new passenger car registrations in Europe in 2025: this is the share that plug-in hybrids now occupy. In Germany, this figure is even close to 11%. On paper, these vehicles embody in the eyes of many customers a form of reasonable compromise: a thermal block for long journeys, an electric motor for everyday use, and particularly flattering official emissions.

Example: on a plug-in hybrid BMW M5 equipped with a large 4.4-liter bi-turbo V8 of more than 700 hp, the approval cycle announces between 105 and 118 g/km of CO₂, or as much as a 115 hp Renault Clio TCe equipped with a small three-cylinder.

Manufacturers do not hesitate to tout this versatility as good news both for customers and for the climate. In reality, the equation is less attractive.

The International Council on Clean Transportation (ICCT) has just published the tenth edition of its study From Laboratory to Road, and the conclusions are, obviously, clear. Based on the analysis of data from two sources combined for the first time, namely on-board consumption readings on around 8 million vehicles registered in Europe between 2021 and 2023, as well as data collected on 300,000 vehicles registered in Germany between 2021 and 2024, it shows that the gap between certified and actual PHEV emissions has reached on average 400% in 2023, compared to 265% 2 years earlier. In other words: the gap is not narrowing, it is widening.

Why don't the official figures hold up?

Three main factors explain this drift. First, drivers recharge their vehicles less often than the certification calculations assume. Direct consequence: the heat engine takes over more frequently, and the battery, rarely full, does not play the role attributed to it on paper.

Then, even in “all-electric” mode, the thermal engine regularly intervenes in support, particularly at high load. Finally, having two powertrains makes the car considerably heavier, which mechanically increases its overall energy consumption. The result is precisely quantified: an average difference of 99 grams of CO₂ per kilometer over the period 2021-2023 between the actual values ​​and the declared values.

With around 840,000 new PHEVs registered each year in the European Economic Area, the ICCT estimates that some 20 megatons of unaccounted CO₂ escape annually. Over the period 2021-2025, the bill rises to around 100 megatons, the equivalent of 42 billion liters of fuel consumed outside of any regulatory radar.

Emissions which have nevertheless been integrated into the European Union's CO₂ reduction objectives, as if they had indeed been avoided. It’s not just that PHEVs pollute more than expected, it’s that this phantom pollution has been used as a bargaining chip in climate negotiations.

Manufacturers have been able to post declining fleet averages by selling more of these vehicles, without this translating into a proportional reduction in actual emissions.

Mercedes at the top of the poor ranking

Among the manufacturers, Mercedes stands out unenviably. The leading seller of PHEVs in Europe over the period studied, the brand displays an average gap of 452% between official and actual emissions. Worse still, this gap has almost doubled in 2 years, going from 329% in 2021 to 614% in 2023.

The study also does not spare conventional thermal engines. Between 2018 and 2023, official emissions from new cars in Europe fell by 28%, but actual emissions only fell by 15%. Even after the 2025 utility factor correction, actual PHEV emissions would still remain 18% higher than official values ​​according to the ICCT.

As Jan Dornoff, researcher at ICCT and co-author of the study, points out: “The gap for plug-in hybrids is shocking, but this should not make us forget that that for conventional vehicles, which still represent the majority of sales in Europe, is also considerably high, at 20%. »

Regulatory corrections, but already threatened

The European Commission has not remained completely inert in the face of these findings. In 2025, the utility factor (the coefficient supposed to reflect the real share of kilometers traveled in electric mode in the calculation of approved emissions) was revised to better match the uses observed in the field. Which also leads certain manufacturers to react, such as BMW which plans to “sanction” its customers who do not recharge their PHEV enough.

Concretely, the utility factor is the coefficient which estimates the share of kilometers actually traveled on electric power. Until now, approval assumed that a PHEV with 60 km of electric range drove on battery power more than 80% of the time: the 2025 revision brings this rate down to around 54%, and that planned for 2027 would bring it down to around 34%, closer to real uses.

A new correction is planned for 2027. But at the same time, the ongoing negotiations in the European Parliament on CO₂ reduction targets for passenger cars and light commercial vehicles include a preliminary project which would precisely suspend these future corrections. One step forward, two steps back in short.

Sonsoles Díaz, researcher at the ICCT, also comments: “Plug-in hybrids consume much more fuel on the road than official figures suggest. As long as regulators do not correct this flaw, manufacturers will continue to declare emissions unrelated to those produced in real conditions. »

Peter Mock, Europe director of the ICCT, agrees: “even after the 2025 correction, real emissions remain poorly estimated. The new models do not emit less than their predecessors, they emit more. Contrary to what some manufacturers claim that their customers drive more in electric mode, on-board consumption data tells a different story. »

Plug-in hybrids aren't a bad idea in and of themselves. Used correctly, recharged regularly, on short and urban journeys, they can effectively reduce fuel consumption. But this ideal use remains in the minority. And for once, given the on-board mass and the gas plant that this represents, an equivalent thermal and thermal only model will obviously emit less CO₂. Conversely, an electric car releases 73% fewer emissions over its entire life cycle according to another ICCT study.

And as long as approval protocols continue to rely on behavioral hypotheses disconnected from reality, the assessments will remain what they are: a theoretical projection which serves commercial strategies more than the environment, a subject that Frandroid regularly deciphers in the face of preconceived ideas.

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