Air transport is not fully comparable to other transport modes : it usually answers specific needs for long or very long distance travel, quicker trips, or when no substitute – such as videoconferencing – is applicable. But it is also increasingly used for shorter distance travels of a few hundred kilometres, due to cheaper fares.
The increased use of aviation has a lot to do with specific benefits granted to this transport sector. Its greenhouse gas emissions are largely excluded from national climate statistics and reduction commitments under the Kyoto Protocol, and several subsidies and tax exemptions are in place. Meanwhile, its environmental impact is far from negligible, notably its carbon emissions.
Thus, its use can be questioned : while it may be relevant for some travel needs, a widespread development of air transport would simply be unsustainable. As an illustration, the business-as-usual scenario of ICAO (International Civil Aviation Organisation) foresees a 300 % to 700 % global increase in air travel emissions by 2050 if nothing is done !