Aviation and the Global Atmosphere

Aviation and the Global Atmosphere
indirect, where the climate species is not the same as the emitted species-as with modified cirrus cloud coverage resulting from particles and particle precursors.
1.3.1. Carbon Dioxide
The behavior of CO 2 within the atmosphere is simple and well understood. There are no important formation or destruction processes that take place in the
atmosphere itself. Atmospheric sources and sinks occur principally at the Earth's surface and involve exchanges with the biosphere and the oceans (e.g., Schimel et
al., 1995, 1996). The effect of CO 2 on climate change is direct and depends simply on its atmospheric concentration. CO 2 molecules absorb outgoing infrared radiation
emitted by the Earth's surface and lower atmosphere. The observed 25-30% increase in atmospheric CO 2 concentrations over the past 200 years has caused a
warming of the troposphere and a cooling of the stratosphere.
There has been much discussion about how stabilization of CO2 concentrations might be achieved in the future (e.g., IPCC, 1996a, 1997a,b). One of the most
important factors is the accumulated emission between now and the time at which stabilization is reached. The way in which annual emissions vary over time is less
important. Two findings from these IPCC reports are worth noting:
If global anthropogenic CO 2 emissions were maintained near 1994 levels, the atmospheric concentration would continue to rise for more than 200 years; by the
end of the 21st century, it would have reached about 500 ppmv (compared to its pre-industrial value of 280 ppmv).
A range of carbon cycle models indicates that stabilization of atmospheric CO 2 concentrations at 450, 650, or 1000 ppmv could be achieved only if global
anthropogenic CO 2 emissions drop to 1990 levels by approximately 40, 140, or 240 years from now, respectively, and substantially below 1990 levels
subsequently.
Table 1-1: Species contributing to climate and ozone change.
Emitted Species Role and Major Effect at Earth's Surface
CO 2
Troposphere and Stratosphere
Direct radiative forcing warming
H 2 O Troposphere
Direct radiative forcing warming
Increased contrail formation radiative forcing warming
Stratosphere
Direct radiative forcing warming
Enhanced PSC formation O 3 depletion enhanced UV-B
http://www.ipcc.ch/ipccreports/sres/aviation/016.htm (2 von 6)08.05.2008 02:41:29
Modifies O 3 chemistry O 3 depletion enhanced UV-B