Which climate relevant emissions are taken into account?
The combustion of kerosene through aircraft causes the emission of several greenhouse gases. The climate effect of these gases, and the effect of the individual gases in different elevations, are quite different. Some gases have positive and negative impacts on the greenhouse effect. These differences are accounted for in the conversion of the various greenhouse gasesOther GHGs into the effect (or climate effect) of CO2 (so called CO2 equivalents). It is for this reason the reference is often made to CO2 only (or CO2-eq) rather than the emission of various greenhouse gases. The IPCC (1999) has quantified the most important emissions cause by aviation as being:
Carbon dioxide (CO2), emitted through the combustion of fossil fuels. The combustion of 1 kg of kerosene causes the emission of 3,15 kg of CO2. After emission CO2 remains in the atmosphere for approximately 100 years. CO2 is one of the primary greenhouse gases, and for this reason is often used for comparability (CO2 equivalents).
Water vapour is found naturally in the atmosphere, and plays a vital role in the natural greenhouse effect, without which life on planet earth would be unthinkable. Aircraft however, through the combustion of kerosene, also cause water vapour, visible as contrails in the sky, and contribute to the anthropogenic greenhouse effect.
Nitrous oxides (NOx) are comprised mainly of nitrogen monoxide (NO) and nitrogen dioxide (NO2). The emission of nitrogen oxides by aircraft has two main effects. On the one hand they reduce the concentration of the greenhouse gas methane, which leads to a reduction of the greenhouse effect. On the other hand, the emission of nitrous oxides at cruising altitude produces ozone. The production of ozone amplifies the greenhouse effect. In the IPCC reference scenario, aviation will cause the concentration of ozone to rise by 13% by 2050.
Sulphur oxides (SOxO) and soot are also emitted during the combustion of kerosene. These play direct and indirect roles in changing climate and ozone chemistry. Their climate effect is more difficult to quantify, and considered scientifically uncertain.
IPCC (1999): Aviation and the Global Atmosphere. A Special Report of IPCC Working Groups I and III in collaboration with the Scientific Assessment Panel to the Montreal Protocol on Substances that Deplete the Ozone Layer. Cambridge University Press, UK.
Available online: www.grida.no/publications/other/ipcc_sr/