25 July 2019

What influence does aviation have on the climate?

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The climate debate is one of the dominant topics in Switzerland before the federal elections in autumn. The industry is threatened with more severe operating restrictions and a CO2 tax on airline tickets.

General Information

Emissions from global aviation have an Impact on the climate, both through the release of the greenhouse gas CO2 from fossil energy sources and through other effects (not CO2 effects).

Influence of CO2 from fossil sources

Each combustion of fossil materials (e.g. gasoline, diesel, kerosene, gas, coal), primarily produces carbon dioxide (CO2) and water vapor as combustion products. CO2 is non-toxic and in this sense not a pollutant. However,it is one of the most important greenhouse gases in the atmosphere and is very important for the Earth's carbon cycle, which takes place between the air, land and oceans. CO2 emitted into the atmosphere has a very long lifetime until it is bound (e.g. in a plant). The average service life is expected to be about 100 years. However, a significant proportion of the emissions remain in the atmosphere and last much longer than greenhouse gases. The additional CO2 emitted today, accumulates in the atmosphere and unfolds its effect for a very long time in the future, regardless of the source. This is a major and important difference from other influences of aviation on the climate.

Other effects (not CO2 effects)

Other effects (not CO2 effects) include emitted gases that do not directly affect the climate, such as nitrogen oxides and soot particles, which influence the composition of the atmosphere and cloudiness. A peculiarity of the ""non-CO2 effects"" from aviation is that these effects do not behave like the emissions of a greenhouse gas:

  • They can have a warming or cooling effect on the earth's temperature.
  • In principle, there is no pronounced ""enrichment effect"" of the greenhouse effect over the long term as with CO2.
  • The additional effects are short-lived (minutes, hours, days) compared to the greenhouse effect of CO2 emissions.

The reduction of CO2 emissions brings clear and long-term benefits, whereas the reduction of ""non-CO2 effects"" has high uncertainties regarding its effects and can even generate more CO2. Therefore, for example, the compensation of CO2 emissions should relate only to the effective CO2 emissions.

For the estimation of climate costs from aviation, the Technical Environmental Committee of the International Civil Aviation Organization (ICAO), which is responsible for the development of global environmental standards for aircraft, used the 100-year "Global Warming Potential" ( GWP) with a value of 1.35, taking into account the high uncertainty and the lack of comparability of cloud effects with greenhouse gases. The estimates of the temperature changes to be expected from the CO2 and "non-CO2 effects" provide evidence that CO2 emissions are absolutely dominant and that it is right to primarily reduce effective CO2 emissions in aviation in order to contain the rise in temperature on Earth.

Global classification of air traffic

According to the International Endergy Agency (IEA 2018), the total CO2 emissions from global aviation account for 2 - 2.5% of global man-made fossil CO2 emissions.


Classification of Swiss air traffic

The annual CO2 emissions from air traffic within Switzerland and for international air traffic from Switzerland to destinations abroad amount to 5,4 million tonnes of CO2. The domestic share is around 0,1 million tonnes of CO2 (excluding Military aviation).

Since kerosene today is extracted almost entirely from fossil sources, CO2 emissions from aviation activities can be directly related to CO2 emissions from other fossil fuel-fired processes. Due to its properties for flight safety and its very high energy content per kg, kerosene will probably remain the decisive energy source for flight operations in the long term. Great efforts are therefore being made to extract the carbon from the atmosphere either directly or indirectly during the production of the fuel and to cover the production energy from renewable energy sources (CO2 neutrality) or to save fossil CO2 elsewhere (CO2 compensation).