Will flying remain a climate killer? | Knowledge & Environment | DW

The share of global aviation in the increasing greenhouse effect was almost six percent in 2019. 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. But now air traffic is increasing according to the International Aviation Organization (IATA).– and with it the 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 of airplanes make the biggest contribution to global warming.

1. Less climate damage with flight routes without contrails

In addition to CO2, the burning of kerosene when flying also produces so-called contrails, thin white clouds of ice crystals. They are formed from emissions from aircraft. The low temperatures at an altitude of eight to twelve kilometers turn water vapour, soot and sulfur into ice crystals that can remain in the air for hours. The contrails of air traffic keep heat in the atmosphere like under a bell and thus significantly increase the climate effect. Recent studies showthat 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, How to optimize flight routesthat 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 around one to five percent more time and fuel. At the same time, a reduction in non-CO2 effects of around 30 to 80 percent is achieved.”

The EU wants to reduce these so-called non-CO2 effects and such effects in the future include in European emissions trading. From 2025, airlines should according to a preliminary agreement in the European Parliament regularly report on their non-CO2 effects.

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

When kerosene is burned from crude oil, a lot of CO2 is produced, as well as ozone and other greenhouse gases at high altitudes. The CO2-free alternative is the 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 generated in an electrolysis process, and then CO2 is added synthetically the e-kerosene.

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The problem: A lot of solar and wind power is required for the cost-effective production of e-kerosene, and so far there has been too little of it. Also new production facilities for green hydrogenCO2 capture from the air (direct air capture) and synthetic fuels have yet to be built.

3. Biokerosene made from vegetable oil for flying

Another option is to fill up with biokerosene, which can be made from old cooking oils, 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 in view of the scarcity of arable land for the production of oil plants very limited and also controversial.

Negotiators from the EU Parliament and the EU states have now agreed that biofuels and e-kerosene will be added to conventional fossil kerosene in the EU in the future must. 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 aircraft: climate-friendly niche for short-haul routes

Airplanes with electric motors and batteries could fly in a very climate-friendly way. These do not cause any additional climate effects such as contrails. But the big problem are currently 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 the optimization for batteries and machines. The Israeli manufacturer Eviation Aircraft is currently constructing an all-electric jet for nine people. He should in the future have a range of 445 kilometers and fly at around 400 km/h.

At the Norway wants to be a pioneer in regular service with electric aircraft: 2026 the first battery aircraft with space for 12 people are planned there connect the coastal cities of Bergen and Stavanger, 160 kilometers away.

Image of a new type of aircraft that is particularly aerodynamic.  Wings and aircraft body merge into one another.  Concept aircraft AirbusZEROe with Blended Wing Body Concept.

It is not yet clear whether this design will be built for a hydrogen aircraft.

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, which can efficiently drive propellers.

Jet engines for long-haul aircraft can also be powered by hydrogen, but they would be less efficient.

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The Airbus group wants to have a passenger aircraft by 2035 bring to the market with hydrogen propulsion. According to one, hydrogen aircraft could McKinsey study 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 liquefies 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.

Infographic Climate-impacting emissions per 1000 km from different modes of transport

6. Flying less and more efficiently helps for 1.5 degree course

Completely emission-free and therefore air traffic will not become climate-neutral by 2050, even in the optimistic scenarios. However, experts assume that an ambitious conversion could reduce greenhouse gas emissions from flying by around 90 percent. However, additional measures are necessary for this, according to the authors of one current study in the renowned journal Nature.

Fossil kerosene could by mid-century completely replaced by green hydrogen and e-kerosene and flight routes without climate-damaging contrails would be possible. However, some climate effects remain even when flying with e-kerosene, emphasize the scientists.

The central element for climate protection is therefore to avoid flights as far as possible and to give preference to climate-friendly means of transport, also emphasizes the German Federal Environment Agency.

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 integration of environmental costs into the prices of flight tickets is helpful in the implementation of all these measures, emphasizes the European environmental umbrella organization Transport and Environment in its Roadmap to more climate-friendly aviation. So far, airlines have paid nothing for theirs 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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