The RFI factor - what is it?
The abbreviation RFI stands for "Radiative Forcing Index". The RFI is an attempt to fully record the climate impacts of air travel. Radiative forcing is another term for warming effect. For aviation emissions and their effects on the global climate, this does not depend solely on the amount of carbon dioxide emitted. Aircrafts cause (besides carbon) also other greenhouse gases that are emitted in particularly sensitive layers of the earth's atmosphere. These are e.g. nitrogen oxides or soot particles and water vapor.
In order to be able to estimate the overall climate impacts caused by air traffic, the carbon emissions are multiplied by the so-called RFI factor. There are still scientific uncertainties about the exact level of this factor. The Intergovernmental Panel on Climate Change IPCC gives an average RFI factor of 2.7. Other scientists differentiate between short, medium and long haul flights and assume an RFI factor of 1.9 to 4.7.
The Federal Environment Agency of Germany emphasizes that i.a. the emission of nitrogen oxides and the promotion of increased cloud formation through the emission of soot particles and water vapor are important for the RFI. However, since the effects of these substances cannot yet be determined with the same degree of certainty as the other effects of air traffic, the RFI should be used as a range between 3-5. This means that the climate impact of air traffic is 3-5 times as high as the impact of the emitted carbon dioxide alone. Decisive for the determination of the RFI is among other things the altitude, which is highest on long-haul flights and which are therefore the most harmful to the climate.
Taking into account the RFI factor, the climate damage for which air traffic is globally responsible amounts to 6-10% of the total man-made greenhouse effects. However, the polluters are only a very small part of the world population.