Nearly all the 1.2 billion or so cars that ply the world’s roads today run on gasoline. A tiny fraction use biofuels, electricity or hydrogen, but that share is projected to grow steadily. And while these alternative and electric vehicles can reduce driving emissions, they still have an environmental footprint.
As the world slowly transitions to low-carbon road transport, it’s important to compare this footprint, write researchers in a new paper published in the journal Earth’s Future. In the study, they present a detailed analysis of the carbon, land and water footprint of cars that run on different energy sources.
Their number-crunching shows some unexpected results. Solar-powered EVs, perhaps unsurprisingly, have the smallest environmental footprint. But biofuel-driven cars have the largest footprints overall, surpassing conventional gasoline cars, which have the second-largest carbon footprint. “Interestingly, gasoline-based cars have the smallest associated land footprint per driven km and the second smallest water footprint,” the researchers write.
All alternative fuels and electricity require land, water and energy to produce. Biofuels, for instance, require copious amounts of water and land. Hydrogen and battery-electric vehicles run emissions-free, but the hydrogen and electricity can still come from dirty fossil fuels.
While several past studies have looked at the land and water footprint of biofuels. Bunyod Holmatov and Arjen Hoekstra of the University of Twente wanted to compare the carbon, land and water footprint of all different vehicle technologies.
Using data from previous studies and public databases, they calculated the three footprints of midsize cars driving a kilometer on conventional gasoline; a 20% biodiesel blend (B20), with the biodiesel coming from rapeseed; 85% blend of sugar beet-based bioethanol (E85); electricity generated from burning sugarcane; electricity generated from solar panels; and hydrogen, produced through electrolysis using solar electricity.
Switching from gasoline to alternative fuels creates all sorts of emissions, land and water use tradeoffs, they found. Switching to EVs cuts emissions by 96% for bioelectricity and 100% for solar electricity. A solar-based hydrogen car cuts emissions entirely but requires 58% more water than a gasoline car.
A B20-fueled car has the worst environmental performance, increasing emissions by 12% while requiring 683 times more water. An E85-based car, meanwhile, can cut emissions by half but has the second- largest land and water footprints, requiring 655 times more water compared to gasoline.
“The logical choice of future transport is thus diffusion of electric and hydrogen vehicles based on (non-biomass) renewable energy sources,” the research duo conclude.
Source: Bunyod Holmatov, Arjen Y. Hoekstra. The environmental footprint of transport by car using renewable energy. Earth’s Future, 2020.