Updated assessment of aviation's impact on the atmosphere
In an update of the 1999 assessment of aviation impacts on climate change and ozone depletion by the Intergovernmental Panel on Climate Change (IPCC), a new study has detailed recent research on aviation emissions and investigated the potential for using alternative aviation fuels.
Aviation levels have increased substantially since the 1960s and are projected to rise in the future. Emissions from aircraft engines change the chemistry of the atmosphere and can modify the global climate and deplete the ozone layer.
Undertaken as part of the EU ATTICA1
project, the research confirms the major effects on climate change resulting from air traffic emissions, including: the warming impact of CO2
, soot particles, water vapour, contrails (condensation trails from engines) and increased cirrus cloud formation; and the cooling impact from sulphate particles. These results are for subsonic aircraft that fly at altitudes ranging from 8-12 km.
In addition, aviation nitrogen oxide emissions have both a warming effect through the formation of ozone, a greenhouse gas (GHG), in the lower atmosphere, and a cooling effect, through the destruction of methane, also a GHG. The overall impact on the climate from nitrogen oxide emissions is probably warming. However, nitrogen oxide emissions from subsonic aircraft do not appear to deplete ozone in the upper atmosphere.
Estimates suggest aviation contributed about 3.5 per cent (excluding the effects on increased cloudiness) to the total climate warming from human activities in 2005, and this figure is expected to rise to 4 to 4.7 per cent by 2050. In 2005, 2.5 per cent of man-made CO2
emissions came from aviation. Projections suggest CO2
from aviation in 2050 will increase 2.7 to 3.9 times, compared with 2000 levels.
Further work is needed to understand and quantify the effects of aviation on clouds, including contrails, increased cirrus cloud development from spreading contrails and altered properties of clouds from soot emissions. Nevertheless, the effect of contrails and probable additional cloud formation is likely to have an overall warming impact on the climate.
Technological advances have the potential to mitigate some of aviation's impacts on climate change and the ozone layer but could take some time to reach the market: aircraft are generally in use for around 20-25 years and although feasible, technology that significantly reduces emissions of CO2
, nitrogen oxide, water and aerosols typically takes time to develop. In addition, technological advances would probably require trade-offs between reducing nitrogen oxide emissions and contrail development (at a cost of higher fuel consumption) and reducing CO2
emissions through lowering fuel consumption. Operational changes, such as adjusting flight altitudes and times of flights, could potentially cut down contrail formation and reduce the impact on the climate.
Conventional kerosene jet fuels could be replaced with alternative fuels, such as liquid hydrogen or biofuels. Liquid hydrogen produces water and nitrogen oxide, but not carbon emissions. Overall climate impacts depend on the energy sources used to produce the liquid hydrogen. Substantial changes to the aircraft design, general infrastructure and fuel production would be necessary and would probably only occur as part of a wider hydrogen-fuelled economy.
- ATTICA (European Assessment of Transport Impacts on Climate Change and Ozone Depletion was supported by the European Commission under the Sixth Framework Programme. www.pa.op.dlr.de/attica
Lee, D.S., Pitari, G., Grewe V. et al
. (2010) Transport impacts on atmosphere and climate: Aviation. Atmospheric Environment
. 44: 4678-4734.
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