Before the COVID-19 pandemic, when the global aviation sector was flying high in 2019, it contributed about 6% of the planet-warming greenhouse gases in our atmosphere. A year later, as the industry was crippled by pandemic-related flight cancellations, that number had dropped by 43%. Last year, it was still 37% lower.
But according to the industry body International Air Transport Association, air transport continues to grow.
Greenhouse gas emissions are also increasing. In response, the European Parliament announced a proposal to introduce environmental labels for air travel from 2025. The system will serve to inform passengers about the weather footprint of their flights.
Carbon dioxide accounts for only a third of the global warming effect attributed to air travel. Two-thirds are caused by other factors, most notably the condensation trails, or contrails, left behind by aircraft.
Alternate flight paths may prevent contrails
Contrails—those narrow, white clouds that trace airplanes across the sky—are formed when jet fuel, which includes kerosene, burns. At average cruising altitudes between 8,000 and 12,000 meters (about 26,000 to 40,000 feet), the low temperature causes the water vapor to condense around the soot and sulfur left by the jet emissions. As a result ice crystals can remain suspended in the air for hours.
As in a greenhouse, traps heat in the atmosphere, greatly increasing the impact of flight on the world’s climate. Recent studies have shown that when it comes to global warming, contrails are about 1.7 times more harmful than CO2 emissions.
On the plus side, contrails are relatively easy to avoid. Using satellite data, flight planners can adapt aircraft routes to avoid weather patterns that favor the formation of contrails. Pilots can also fly their jets 500 to 1,000 meters below, for example, where the temperature is not freezing.
“These changes do not require much effort,” said Markus Fischer, divisional director of the German Aerospace Center, adding that this would mean between 1 and 5% more fuel and flight time. However, he told DW, this would result in a 30 to 80% reduction in the warming effect from factors other than CO2, he said.
The European Union aims to include these non-CO2 climate impacts in future European emissions trading agreements. Airlines will have to start reporting such pollutants from 2025, according to a preliminary agreement reached in the European Parliament.
Producing e-kerosene with green energy
Burning petroleum-derived kerosene produces a lot of CO2 and, at high altitudes, other greenhouse gases such as ozone. A CO2-free alternative is e-kerosene.
E-petroleum can be produced in an environmentally neutral manner using green electricity, water and CO2 released from the air. First, hydrogen is generated using a process involving electrolysis, and then CO2 is added to produce synthetic e-kerosene.
The problem is that to be cost-effective, e-kerosene needs to be made with plenty of solar and wind power – and so far, this renewable energy isn’t enough. New production plants for green hydrogen, CO2 direct air capture and synthetic fuels should also be built.
Can airplanes be fueled by cooking oil?
Another option for planes is refueling with biokerosene, which can be made from rapeseed, jatropha seeds or old cooking oil. Small-scale production plants already exist, but manufacturers may need to expand capacity to keep up with demand. Intensive production of biokerosene is also limited by the lack of arable land – the use of which is itself controversial, as it prevents taking up the space needed to grow food.
Under European Commission proposals, biofuels and e-kerosene will be mixed with traditional fossil kerosene from 2025. The share of biofuels in this mix will increase by 2% per year to reach 70% by 2050. The offer is yet to come. pass
Battery-powered short-haul flights on the horizon
With electric engines and batteries, flights can avoid producing direct emissions or heat-trapping contrails. But current batteries are too heavy and have insufficient storage capacity, limiting aircraft to short ranges of a few hundred kilometers.
Many companies are in the process of tinkering with battery and aircraft optimization. Israeli manufacturer Aviation Aircraft, for example, is building an all-electric jet to seat nine passengers. The private jet is expected to have a range of 445 kilometers and a top speed of 400 kilometers per hour (about 250 miles per hour).
Norway aims to launch regular electric flight service for the first time in less than three years. The country plans to connect the coastal cities of Bergen and Stavanger, some 160 kilometers away, from 2026 with a flight serviced by battery-powered aircraft with space for 12 passengers.
Hydrogen aircraft show promise, but not ready
Hydrogen-powered small planes have been in the news lately. These aircraft use hydrogen fuel cells to generate electricity and efficiently power the aircraft’s propellers. Jet engines in long-haul aircraft can also run on hydrogen but will be less efficient.
European aircraft manufacturer Airbus plans to launch a hydrogen-powered passenger plane by 2035. These planes could account for more than 30 percent of global air traffic by 2050, according to a study by global consulting firm McKinsey.
But hydrogen-powered planes pose many challenges. The volatile gas is only liquefied at minus 253 degrees Celsius (minus 423 degrees Fahrenheit), and must be stored under high pressure in special tanks. This means additional space and weight requirements for the airplane, and those plans are still being developed. Additionally, airports will need to develop new refueling infrastructure for hydrogen-powered aircraft.
One surefire way to reduce emissions: fly less
Even under the most optimistic scenarios, air travel will not be completely emissions-free by 2050. Experts believe that if the industry implements ambitious restructuring plans – completely replacing standard jet fuel with green hydrogen and e-kerosene, and rerouting planes to prevent contrails. – It can reduce greenhouse gas emissions by up to 90%.
However, a recent study in the scientific journal Nature noted that even a complete switch to e-kerosene would have residual negative effects on the climate. Therefore, it is important to avoid all but essential flights and prioritize climate-friendly modes of transport, Germany’s federal environment agency UBA said.
Aviation experts have called for new, lighter aircraft with optimized wings, the use of propellers instead of jet engines and reduced wind speeds. They point out that these measures could reduce fuel use by about 50% compared to today.
Integrating environmental costs into airline ticket prices will help implement all these measures, says the European Clean Transport Campaign Group Transport and Environment (T&E). Airlines currently pay nothing for their contribution to the climate crisis. Incorporating environmental costs into air fares would be a reasonable way to promote the restructuring of the aviation industry and facilitate the switch to climate-friendly modes of transport, according to T&E.