E-kerosene, climate-friendly flight routes and new aircraft can make flying more climate-friendly. What is the point – and how far are these alternatives?
So far often ignored and underestimated: The climate impact of contrails in air traffic
In 2019, global aviation accounted for almost six percent of the increasing greenhouse effect. Because many flights were canceled in 2020 during the corona pandemic, 43 percent fewer greenhouse gases were emitted than in the previous year; in 2022 it was 37 percent fewer. However, according to the International Aviation Organization (IATA), air traffic is now increasing again and so are emissions.
The emission of CO2 causes only about a third of the greenhouse effect in air traffic, two thirds are caused by so-called non-CO2 effects. The contrails from airplanes make the greatest contribution to global warming.
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1. Less climate damage with flight routes without contrails
When flying, the burning of kerosene produces not only CO2 but also so-called contrails, narrow white clouds of ice crystals. They are formed from emissions from aircraft. Due to the low temperatures at an altitude of eight to twelve kilometers , water vapour, soot and sulfur turn into ice crystals that can stay in the air for hours. The contrails of air traffic retain heat in the atmosphere like under a bell and thus significantly increase the climate impact. Current studies show that contrails cause around 1.7 times more climate damage than CO2 emissions from flying.
The positive: contrails are relatively easy to avoid.
With the help of weather data, flight routes can be optimized so that aircraft can avoid certain weather zones that favor contrails. For example, you can fly 500 to 1000 meters lower. “It doesn't take that much effort,” explains Markus Fischer, divisional director of the German Aerospace Center (DLR) to DW. “That means: You need about one to five percent more time and fuel. At the same time, a reduction of the non-CO2 effects in the order of 30 to 80 percent is achieved.”
The EU wants these so-called Reduce non-CO2 effects in the future and include such effects in European emissions trading. According to a provisional agreement in the European Parliament, airlines are to report regularly on their non-CO2 effects from 2025.
Plant for the production of e-kerosene in Germany. The electricity comes from wind turbines, Co2 is extracted from the air and from a biogas plant.
2. No CO2 emissions with e-kerosene from green electricity
Burning kerosene from petroleum produces a lot of CO2 and at high altitudes also ozone and other greenhouse gases. The CO2-free alternative is so-called e-kerosene. E-kerosene can be produced climate-neutrally with green electricity, water and CO2, which is extracted from the air. In a first step, hydrogen is produced in an electrolysis process, then e-kerosene is produced synthetically by adding CO2.
The problem: A lot of solar and wind power is required for the cost-effective production of e-kerosene needed, and so far there are still too few of them. New production plants for green hydrogen, CO2 separation from the air (direct air capture) and synthetic fuels have yet to be built.
3. Bio-kerosene from vegetable oil for flying
Another option is to fill up with bio-kerosene, which can be made from used cooking oil, rapeseed or jatropha oil. Smaller production facilities already exist for this. However, the production capacities would also have to be greatly expanded here and the production of large quantities of biokerosene is very limited and also controversial in view of the scarcity of arable land for the production of oil plants.
Negotiators from the EU Parliament and the EU states have now agreed that biofuels and e-kerosene must be added to conventional fossil kerosene in the EU in the future. The proportion of alternative fuels in the aircraft kerosene mix should be at least two percent from 2025 and steadily increase: to 6 percent in 2030, 20 percent in 2035, 34 percent in 2040, 42 percent in 2045 and finally 70 percent in 2050. The agreement still has to be formalized be confirmed by Parliament and the EU states.
4. Battery-powered aircraft: climate-friendly niche for short-haul flights
Aircraft with electric motors and batteries could fly in a very climate-friendly manner. These do not cause any additional climate effects such as contrails. But the big problem at the moment is the heavy batteries and their weak storage capacities, which would only last for short distances of a few hundred kilometers.
Various companies are currently working on optimizing batteries and machines. The Israeli manufacturer Eviation Aircraft is currently constructing a fully electric jet for nine people. In the future, it should have a range of 445 kilometers and fly at around 400 km/h.
Norway wants to be a pioneer in scheduled service with electric aircraft: in 2026, the first battery-powered aircraft with space for 12 people are to be built there Connect the coastal cities of Bergen and Stavanger, 160 kilometers away.
It is not yet clear whether this design for a hydrogen aircraft will be built.
5. Hydrogen aircraft have yet to be developed
Future scenarios for aircraft that fly with hydrogen are currently receiving a lot of attention. The hydrogen generates electricity in a fuel cell that can efficiently drive propellers.
Jet engines for long-haul aircraft can also be operated with hydrogen, but they would be less efficient.
The Airbus group wants to bring a hydrogen-powered passenger aircraft onto the market by 2035. According to a study by McKinsey, hydrogen aircraft could account for between 13 percent and more than 30 percent of air traffic in 2050.
However, there are numerous challenges when powering aircraft with hydrogen. The gas only becomes liquid at minus 253 degrees Celsius and has to be stored under high pressure in special tanks. This requires a lot of space and additional weight, corresponding aircraft have to be newly developed for this technology. In addition, a new infrastructure for refueling with hydrogen will have to be built at airports.
6. Flying less and more efficiently helps for a 1.5 degree course
Even in the optimistic scenarios, air traffic will not be completely emission-free and thus climate-neutral by 2050. Experts assume, however, that ambitious conversion could reduce emissions of greenhouse gases when flying by around 90 percent. However, additional measures are necessary for this, according to the authors of a current study in the renowned journal Nature.
Fossil kerosene could be completely replaced by green hydrogen and e-kerosene by the middle of the century and flight routes without climate-damaging contrails would be possible. However, the scientists emphasize that some of the climate effects remain even when flying with e-kerosene.
The German Federal Environment Agency also emphasizes that avoiding flights and preferring climate-friendly means of transport is a key element in climate protection .
Aviation experts such as Markus Fischer from DLR also see savings effects from new, light aircraft models with optimized wings, propellers instead of jet propulsion and a reduction in flight speed. This could save around 50 percent of the fuel compared to today.
The European environmental umbrella organization Transport and Environment emphasizes in its roadmap to more climate-friendly aviation that the integration of environmental costs into the prices of flight tickets is helpful when implementing all of these measures. So far, airlines have paid nothing for their climate damage. A corresponding integration of the costs would be fair, could promote the conversion of aviation and would facilitate the switch to climate-friendly means of transport.
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Cheap on government and staff costs
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