English
The impact of air-traffic on our climate
The atmosfair advisory board regularly discusses recent scientific findings in the area of air transport and global warming. The board addresses mainly two issues:
What impacts do the exhausts of aircraft engines have on the atmosphere, and especially in high altitudes?
This question has been well answered by science by now. The greatest contribution to global warming stem from the following emissions and effects:
The CO2 itself, as direct by-product of the combustion, the formation of cirrostratus clouds and / or contrails (linear clouds), the formation of the greenhousgas ozone in a sensitive atmospheric layer as well as the cooling effect of methane decomposition.
- Climatic impact of air traffic and RFI-factor, based on IPCC (2007)
How can these effects be taken into account in the emissions calculation, so that the passenger gets a true impression of the environmental impact of his flight?
While CO2 is always produced and takes effect globally over a period of many decades, the ozone as well as the cirrostratus clouds and contrails have a lifetime of hours or maximum days and under special conditions: The atmosphere needs to be humid and cold enough to allow contrails to persist for several hours. Nevertheless, contrails drive climate change locally much more than CO2. Varying life time and different spacial distribution impedes a simple comparison of these diverse effects.
The International Panel on Climate Change - IPCC has established a method for this purpose in 1999: This method concentrates on the atmosphere at a fixed point in time (e.g. 2005) and for this point in time summes up the warming of all known emissions and effects of the entire world air transport since 1950. This means that the average contrails of the year 2005 are taken into account in this calculation, but not those of 2004, which have disappeared in 2005 due to their short life-time. By contrary, CO2 produced in a flight of the year 1950 is included in this calculation, since some fraction of the 1950 CO2 is still part of the 2005 atmosphere (and has yet not been taken up by a natural sink). According to this method the effects of CO2, contrails, ozone etc. drive global warming two to five times more than the CO2 alone. These results depend on the length of the time horizon. A time horizon of e.g. 2010 to 2100 leads to different results than a horizon of 1950 to 2005.
In any case, the carbon footprint of air transport is distorted, if only the CO2 is accounted for. Atmosfair uses a factor of 3 on the CO2 to consider the other above effects, following a recommendation of the German Federal Environmental Agency published in 2008.
Because the payable amount of the atmosfair climate contributions is voluntary anyway, it is atmosfair's view that the passenger should be informed about the full ecological footprint, based on the current state of science. Only on this basis can the environmental awareness grow, which is needed for tackling climate change.