Which of the substances emitted by aircraft are responsible for climate change?
Carbon dioxide (CO2): CO2 is the most abundant greenhouse gas. It blocks the radiation of heat from the Earth so that heat is unable to leave the atmosphere, leading to global warming.
Nitrous oxide: because nitrous oxide is broken down more quickly on the Earth’s surface than in the atmosphere, the influence of emissions caused by air traffic is many times greater than that of cars, for example. Nitrous oxide is also responsible for acid rain.
Ozone: protects the Earth’s surface from ultraviolet radiation from the sun, but is also a powerful greenhouse gas.
Water vapour: the process of combustion releases water vapour. Water vapour that is emitted in the upper atmosphere can concentrate in the stratosphere where it contributes to the destruction of the ozone layer.
Methane (CH4): this greenhouse gas is 20 times more harmful than CO2; moreover it takes a very long time for this gas to break down. Its concentration is reduced by nitrogen emissions, thus lessening its greenhouse effect, although this is a delayed effect.
Sulphur dioxide: this contributes to acid rain, although its effect is less than that of nitrous oxide.
Are aircraft vapour trails bad for the climate?
Vapour trails (contrails) reflect incoming solar radiation and so have a cooling effect. However, they also trap the heat radiation from the Earth, which has a warming effect. As the warming effect outweighs the cooling effect, particularly at night, vapour trails do contribute to global warming.
How are the emissions of a flight measured?
They are measured using average emission using average emissions factors as defined by UNEP (the United Nations Environment Programme). These are internationally recognised values that are widely used:
> 0.18 tons of CO2 per 1,000 km for short flights (shorter than 1,000 km)
> 0.11 tons of CO2 per 1,000 km for long flights (longer than 1,000 km)
The emission values used are averages. The calculation of the emissions caused by your flight is based on an ‘average’ airplane carrying an ‘average’ number of passengers.
The emissions of all the gases (see answer to previous question) are calculated by multiplying the amount of CO2 by 2 (COM 2005: Reducing the Climate Change Impact of Aviation. Brussels).
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