Scandinavian languages have given English a number of words: smorgasbord, ombudsman, troll, and, most recently, flygskam, or “flight shame.” It’s the guilt that plagues climate-conscious air travelers: business people who wonder whether their presence at a meeting two time zones away is really indispensable and vacationers who fret that jetting to a beach resort for the weekend isn’t really part of a sustainable lifestyle.
Airplanes are actually only responsible for about 3 percent of global carbon emissions compared with 17 percent for road transport. But they also emit nitrogen oxides, aerosols, soot, and carbon monoxide at high altitudes. This results in cloud formations at altitudes that would otherwise be cloudless. Atmospheric researchers like Andreas Zahn of the Karlsruhe Institute of Technology suspect that these artificial clouds accelerate global warming: “Air transport’s climate impact is up to three times higher than its carbon emissions alone would suggest.”
Subsidizing climate change?
Taxes account for 60% to 70% of the price of gasoline in the Netherlands, France, and the United Kingdom. No EU country, by contrast, taxes jet fuel. The lack of a jet fuel tax is effectively a government subsidy of air travel. Climate activists have long called for the imposition of such a tax. They believe it would spur airlines to conserve fuel and passengers to spurn air travel for climate-friendlier modes of transport.
The alternative to petroleum-based jet fuel is green jet fuel. The global market leader, Finland’s Neste, produces 80% non-fossil jet fuel from fats, oils, waste, and residual materials. But the supply of these inputs is finite. Another option—making green jet fuel from food crops like corn, wheat, and rapeseed—is controversial when, according to the UN, malnutrition affects nearly 800 million worldwide.
A different process is more promising: power-to-liquid: surplus solar and wind power is used to run electrolysis equipment that splits water into oxygen and hydrogen. The hydrogen is then combined with captured carbon dioxide to produce kerosene. This power-to-liquid process, however, uses a lot of energy and is thus itself relatively carbon-intensive.
Using sunlight directly could be even more promising. A sun-to-liquid project is currently under way at a concentrated solar energy facility in Móstoles, located about 20 kilometers southwest of Madrid, Spain. Here, 169 heliostats (big adjustable mirrors) concentrate onto sunlight onto a solar reactor on top of a 16-meter tower. The solar reactor can reach temperatures of up to 1,500 degrees Centigrade (about 2,730 degrees Fahrenheit). This results in a chemical reaction that produces a synthetic gas. The gas is combined with capture carbon dioxide to make green jet fuel.
The Móstoles sun-to-liquid plant produces one liter of green jet fuel per day. Its energy efficiency—currently 5 percent—would have to be at least four times higher for the process to even begin to become cost-effective. And of course the sun has to shine a lot. This technology therefore makes the most sense in arid regions where the sky is usually cloudless: southern Spain, the Sahara, and parts of the Arabian Peninsula. There are also suitable regions in Central Asia, southern Africa, Australia, and North and South America.
Could flight shame propel development?
Although power-to-liquid and sun-to-liquid technologies obviously need to become more cost-effective, researchers concede that green jet fuel probably won’t ever be as cheap as its petroleum-based alternative. In fact, they’d be happy to achieve a price of €1.30 per liter ten years from now. Standard jet fuel typically costs less than half of that (and currently only a quarter).
For now, the price difference between green and standard jet fuel can only be offset by taxes or flight shame: perhaps passengers who want guilt-free air travel would be willing to pay roughly a third more for their ticket so that their flight runs on green jet fuel.