Aviation and the Environment
The growth in aviation has brought significant benefits to society and underpins the global economy. Historically, the principal environmental challenges posed by aviation have been noise and air quality in the vicinity of airports. The need to continue to improve performance in these areas still remains, but the focus has now shifted to CO2 and other emissions because of their implications for climate change.
CO2 emissions
Globally, aviation currently accounts for about two per cent of man-made CO2 emissions, compared with 16 per cent from other forms of transport and more than 30 per cent from electricity and heat supply. Aviation generated CO2 will increase with expected traffic growth. Future emission levels from each sector will be highly dependent on the relative rates of growth and the scale of technological improvements.
Other emissions
Aero engines operating at altitude have additional impacts that contribute to climate change. These impacts relate to emissions of oxides of nitrogen (NOx) and vapour trails, known as contrails, which in turn can form cirrus clouds. The current level of understanding of the impact of contrail-induced cirrus clouds is poor.
NOx emissions lead to the formation of ozone in the region of an aircraft's flight path, which creates a warming effect. NOx emissions also result in a global reduction in the greenhouse gas, methane, giving rise to a cooling effect. The overall impact of NOx is uncertain and could result in either a small net warming or cooling.
Contrails at most last for hours, cirrus clouds for days, ozone for weeks, methane for around a decade and CO2 for more than 100 years. The relative importance of these effects depends on scientific uncertainties that need to be resolved. Account will have to be taken of both the short-term effects and the implications over the very long term. When considering the long-term climate change impacts of a single flight, CO2 effects dominate.
