International aviation traffic has been growing rapidly over recent decades and is forecast to expand significantly in the future.

A recent study has concluded that future greenhouse gas (GHG) emissions from aviation could compromise climate change targets unless demand for flights is restricted.

In 2005, the aviation industry is estimated to have contributed between 3 to 8 per cent of the total manmade warming effect on climate. Although this is a small amount compared with other sectors, global aviation traffic is expected to grow significantly over the next 20 years.

�The biggest increase is expected to come from international traffic, which accounts for over 60 per cent of total aviation emissions. Industry forecasts predict that passenger traffic will rise by 180 per cent and cargo traffic by 220 per cent between 2006 and 2026.

The study preceded the high oil prices of 2008 and the current economic slowdown, both of which may reduce demand for aviation, at least in the short term, which would mitigate some of these emissions. The study modelled aviation emissions for the period 2005-2025. The results suggest that CO2 emissions from international aviation could increase by 111 to 144 per cent (from 416 million tonnes (Mt) to between 876 and 1013 Mt) by 2025. If contributions from other non-CO2 aviation emissions, such as water and nitrogen oxides (NOx), are converted to 'carbon dioxide equivalents' (CO2-e - a measure of impact on global warming), total CO2-e emissions from international aviation could be between 1488 and 1722 Mt in 2025.

To ensure that global temperatures do not rise by 2�C above pre-industrial levels, a commonly cited climate change target, manmade GHG emissions must be reduced1. As part of the strategy to achieve this goal, the EU plans to include international aviation emissions in the emissions trading scheme by 20122, although a number of non-EU countries are against this proposal.

Responsibility for international emissions falls under ICAO3, a United Nations agency formed under the Chicago Convention. The report concludes that measures taken by ICAO to curb aviation emissions have been hampered by:
*�fears that restricting demand could damage the aviation industry with knock-on effects for other sectors such as tourism
*�the legal implications of applying emission levies or carbon prices on aircraft from outside the EU
*�the difficulty of structuring a fair emissions trading scheme on an international scale.

Stabilising emissions is difficult. There have been improvements in air traffic management, carrying capacity, aircraft and engine design, which have resulted in a 40 per cent gain in emission intensity (carbon dioxide emitted per unit of electricity) between 1990 and 2005, although recent rates of improvement have slowed. However, this study predicts that the emission intensity of international aviation would have to fall by a further 32 per cent to prevent emissions from increasing by more than 100 per cent between 2005 and 2025. To stabilise emissions at 2005 levels, the emission intensity would have to be improved by 65 per cent. Current technologies cannot meet these targets. While the study highlights the potential of restricting demand for aviation, such policies are likely to be very unpopular. Other approaches, such as inclusion of aviation in the EU ETS would allow emissions from aviation to be offset by savings in other sectors and may provide a feasible alternative to demand restriction.