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Aircraft Engine Emissions

Aircraft engines produce emissions that are similar to other emissions resulting from fossil fuel combustion. However, aircraft emissions are unusual in such a way that a significant proportion is emitted at altitude. These emissions give rise to important environmental concerns regarding their global impact and their effect on local air quality at ground level.

A comprehensive assessment concerning

A comprehensive assessment concerning aviation's contribution to global atmospheric problems is contained in the Special Report on Aviation and the Global Atmosphere, which was prepared at ICAO's request by the Intergovernmental Panel on Climate Change (IPCC) in collaboration with the Scientific Assessment Panel to the Montreal Protocol on Substances that Deplete the Ozone Layer and was published in 1999. This told us inter alia:
1. aircrafts emit gases and particles which alter the atmospheric concentration of greenhouse gases, trigger the formation of condensation trails and may increase cirrus cloudiness, all of which contribute to climate change;
2. aircrafts are estimated to contribute about 3.5 per cent of the total radiative forcing (a measure of change in climate) by all human activities and that this percentage, which excludes the effects of possible changes in cirrus clouds, was projected to grow.

The Report recognized that the effects

The Report recognized that the effects of some types of aircraft emissions are well understood, revealed that the effects of others are not, and identified a number of key areas of scientific uncertainty that limit the ability to project aviation impacts on climate and ozone.

Against this background, the ICAO Assembly in 2001 urged States to promote scientific research aimed at addressing the uncertainties identified in this Report and requested the Council to continue to cooperate closely with the IPCC and other organizations involved in the definition of aviation's contribution to environmental problems in the atmosphere and the need to take initiatives for a scientific understanding of the problems (Assembly Resolution A35-5 (PDF), Appendix H). This was reiterated by the Assembly in 2007 (Assembly Resolution A36-22 (PDF), Appendix I). ICAO requested the IPCC to include an update of the main findings of the 1999 report in its Fourth Assessment Report (IPCC AR4) published in 2007.

The new findings related to aviation emissions in IPCC AR4

The new findings related to aviation emissions in IPCC AR4 are inter alia:
  • Due to developing scientific knowledge and more recent data estimates of the climate effects of contrails have been lowered and aircrafts in 2005 are now estimated to contribute about 3.0 % of the total of the anthropogenic radiative forcing by all human activities;
  • Total CO2 aviation emissions is approximately 2 % of the Global Greenhouse Emissions;
  • The amount of CO2 emissions from aviation is expected to grow around 3-4 per cent per year;
  • Medium-term mitigation for CO2 emissions from the aviation sector can potentially come from improved fuel efficiency;
  • However, such improvements are expected to only partially offset the growth of CO2 aviation emissions.


Later the IPCC initiated the preparation of the Fifth Assessment Report (AR5), which was scheduled to be completed in 2014. ICAO actively participated in the IPCC working process to ensure that issues related to scientific understanding of aviation’s impacts on global climate are covered in the AR5.  
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