In real-world driving conditions, the CO₂ emissions of plug-in hybrid cars are nearly five times higher than official tests suggest, according to an analysis by the European Environment Agency. Automakers often present plug-in hybrids as a more conventional alternative to fully electric vehicles, as they combine a gasoline or diesel engine with an electric motor and a battery that can be charged from the power grid.
Currently, hybrids account for about 8 to 9 percent of car sales in the EU. Manufacturers are increasing pressure on Europe to allow sales to continue after 2035, despite the EU’s requirement that all new cars must have zero emissions by then.
A Growing Discrepancy
The disparity between real-world CO₂ emissions and test results is widening, based on data from the environmental and transport group T&E. In 2023, plug-in hybrids emitted an average of 139 grams of CO₂ per kilometer in real-world conditions, significantly higher than the 28 grams indicated in official testing. This gap has expanded over the years; in 2021, real emissions were 3.5 times higher than test results, and in 2022, four times higher.
“Plug-in hybrids are still worse for the climate than automakers claim, and the gap with reality has only grown larger,” says Lucien Mathieu of T&E. “The auto industry is urging the EU to look the other way to delay investment in fully electric cars. The European Commission must maintain its stance.”
Reasons for the Disparity
There are several factors contributing to this significant difference in emissions:
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- Test Cycles Don’t Reflect Reality: Official emissions figures are derived from lab tests, such as the WLTP (Worldwide Harmonized Light Vehicles Test Procedure). These tests assume short trips, a fully charged battery, and ideal driving behavior. Under these conditions, plug-in hybrids utilize mostly electric power, resulting in extremely low emissions. However, daily driving conditions are often far less ideal.
- Batteries Are Often Not Charged: Plug-in hybrids need to be charged regularly to operate on electricity. In practice, many drivers forget or skip charging altogether, or lack convenient access to charging facilities at home or work. Once the battery is depleted, the car primarily relies on its combustion engine, which can be less efficient than that of a conventional car due to the additional weight of the battery pack.
- Extra Weight and Complexity: Because hybrids contain both an engine and a battery, they are heavier than traditional cars. This added weight consumes more energy, making the combustion engine particularly inefficient at highway speeds, resulting in higher emissions than test results indicate.
- Driving Habits: Drivers who frequently take long trips, spend significant time on the highway, or drive aggressively benefit little from the electric motor. Their real-world emissions remain much higher than the test values.
- Overly Optimistic Assumptions in Policy: For years, automakers and policymakers have assumed that plug-in hybrids would primarily be driven on electric power—sometimes estimating that 70 to 80 percent of miles would be electric. In reality, the actual share is often much lower, sometimes under 20 percent. This discrepancy between expectations and reality directly leads to increased CO₂ emissions.
