Diesel-powered cars have enjoyed a comfortable market share in Europe for decades, but their decline in popularity continues following numerous diesel-emission cheating scandals and regulatory crackdowns. 

As if diesel cars hadn't already had enough negative press, a new study says "fuel-efficient" diesel vehicles actually produce more lifetime carbon dioxide than do equivalent average gasoline-powered cars.

The study also notes that lower fuel taxes in many European countries deliberately created an uneven playing field for gasoline versus diesel.

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Moreover, relaxed test measures and loose oversight have only amplified Europe's addiction to diesel fuel.

Looking at the average diesel- and gasoline-powered car, the diesel car produces significantly more CO2 over its entire lifetime than a gasoline car.

Diesel cars make 1.6 tonnes more wells-to-wheels carbon emissions than do gasoline cars running E95, a blend of 95 percent gasoline and 5 percent ethanol, according to a Transport & Environment study.

Diesel fuel pump

Diesel fuel pump

Even using a B7 blend of diesel—95 percent diesel and 5 percent biodiesel—the study shows that producing the heavier engines of the diesel cars produce 0.25 more tonnes of CO2.

That adds to the 1.8 tonnes more CO2 it produces during its miles on the road versus a gasoline-powered car fueled with E95, in part because diesel fuel has more energy per volume, which skews its fuel-efficiency ratings against gasoline.

Therefore, in its lifetime, a diesel car will make 42.65 tonnes of CO2 versus 39 tonnes from a gasoline car.

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The comparison is based on 182,000 kilometers (113,000 miles) driven in a diesel car and 175,000 km (108,000 miles) driven in a gasoline vehicle.

However, the analysis doesn't take into account the full number of extra miles diesel cars drive on average.

European tests, meanwhile, measure automakers on tailpipe carbon-dioxide emissions alone—not over a vehicle's lifetime.

Diesel vs gasoline CO2 lifetime production

Diesel vs gasoline CO2 lifetime production

Fuel taxes in many European Union member countries make gasoline 10 to 40 percent more expensive across all such countries, which the study calls "preferential treatment" for diesel fuel.

The study calculates that this "diesel bonus," in the form of the lower taxes, led to a drop in revenue from fuel taxes over time, costing national budgets almost 32 billion Euros in lost tax revenue in 2016.

Despite diesel's travails at the moment, many automakers continue to believe diesel is necessary to meet increasingly stringent future European emission limits.

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New test procedures that actually measure on-road emissions during real-world driving seem likely to reduce diesel's advantage in fuel-efficiency ratings, however; the effects of that reduction have yet to be calculated.

More and more automakers will electrify more and more of their vehicles as countries—most importantly China—move to ban the sale of cars powered by fossil fuels, some as early as 2025.

Thus far, four European countries announced bans to halt the sale of new fossil-fuel-powered cars on various timelines.


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