1. International trade statistics 2006,2007
2. Tourism 2020 vision,2004
3. WTO. World Tourism Barometer. Spain, Madrid: WTO; 2005.
4. Global environmental consequences of tourism;Gössling;Global Environmental Change,2002
5. Penner J, Lister D, Griggs D, Dokken D, McFarland M. Aviation and the global atmosphere, a special report of IPCC working groups I and III in collaboration with the Scientific Assessment Panel to the Montreal Protocol on Substances that Deplete the Ozone Layer. UK, Cambridge University Press: Intergovernmental Panel on Climate Change Publishing; 1999. p. 1–23.