Aviation and the Global Atmosphere

Aviation and the Global Atmosphere
Aviation and the Global Atmosphere
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EXECUTIVE SUMMARY
Other reports in this collection
● Aircraft emissions in conjunction with other anthropogenic sources are expected to modify atmospheric composition (gases and aerosols), hence radiative
forcing and climate. Atmospheric changes from aircraft result from three types of processes: direct emission of radiatively active substances (e.g., CO 2 or water
vapor); emission of chemical species that produce or destroy radiatively active substances (e.g., NOx, which modifies O3 concentration); and emission of
substances that trigger the generation of aerosol particles or lead to changes in natural clouds (e.g., contrails).
● Radiative forcing (RF) is the metric used here (and in IPCC) to compare climate perturbations among different aviation scenarios and with total anthropogenic
climate change. RF is the global, annual mean radiative imbalance to the Earth's climate system caused by human activities. It predicts changes to the global
mean surface temperature: Positive RF leads to global warming. Yet climate does not change uniformly; some regions warm or cool more than others; and
mean temperature does not describe vital aspects of climate change such as droughts and severe storms. Aviation's impacts via O3 and contrails occur
predominantly in northern mid-latitudes and the upper troposphere, leading potentially to climate change of a different nature than that from CO 2 . Nevertheless,
we follow the scientific basis for RF from IPCC's Second Assessment Report and take summed RF as a first-order measure of global mean climate change.
● For the 1992 aviation scenario (NASA-1992*), radiative forcing of climate change from aircraft emissions (gases and aerosols) is estimated to be +0.05 W m -2 ,
which is about 3.5% of total anthropogenic radiative forcing as measured against the pre-industrial atmosphere of +1.4 W m-2 for combined greenhouse gases
and aerosols (and +2.7 W m-2 for greenhouse gases alone). The components of aircraft-induced radiative forcing are as follows: CO 2 , +0.018 W m-2; NOx,
+0.023 W m-2 (via ozone changes) and -0.014 W m-2 (via methane changes); contrails, +0.02 W m-2; stratospheric H2O, +0.002 W m-2; sulfate aerosol
(direct effect), -0.003 W m-2; and black carbon aerosol (soot), +0.003 W m-2. Changes in "natural" cirrus clouds caused by aircraft may result in negligible or
potentially large radiative forcing; an estimate could fall between 0 and 0.04 W m-2. Uncertainty estimates, typically a factor of 2 or 3, have been made for
individual components and are intended to represent consistent confidence intervals that the radiative forcing value is likely (2/3 of the time) to fall within the
range shown. The uncertainty estimate for the total radiative forcing (without additional cirrus clouds) is calculated as the square root of the sums of the
squares of the upper and lower ranges of the individual components.
● Projection of subsonic fleet growth to 2015 (NASA-2015* scenario) results in a best estimate for total aircraft-induced radiative forcing of +0.11 W m-2 in 2015-
http://www.ipcc.ch/ipccreports/sres/aviation/064.htm (1 von 3)08.05.2008 02:42:46