The report does not consider the local environmental effects of aircraft engine emissions or any of the indirect environmental effects of aviation operations such as energy usage by ground transportation at airports. The total amount of aviation fuel burned, as well as the total emissions of carbon dioxide, NO x , and water vapor by aircraft, are well known relative to other parameters important to this assessment. The global mean climate change is reasonably well represented by the global average radiative forcing, for example, when evaluating the contributions of aviation to the rise in globally averaged temperature or sea level. However, because some of aviation s key contributions to radiative forcing are located mainly in the northern mid-latitudes, the regional climate response may differ from that derived from a global mean radiative forcing. The impact of aircraft on regional climate could be important, but has not been assessed in this report.
Ozone is a greenhouse gas.
Aircraft-emitted NO x participates in ozone chemistry. Ozone in the upper troposphere and lower stratosphere is expected to increase in response to NO x increases and methane is expected to decrease. At higher altitudes, increases in NO x lead to decreases in the stratospheric ozone layer. These trends can be attributed largely to human activities, mostly fossil fuel use, land-use change, and agriculture. Tropospheric aerosols resulting from combustion of fossil fuels, biomass burning, and other sources have led to a negative radiative forcing, which, while focused in particular regions and subcontinental areas, can have continental to hemispheric effects on climate patterns.