Tourism creates important multiplier effects on other sectors of the economy. There are three levels of impacts that can be estimated. The direct effects are the economic impacts derived directly from changes in tourist spending as it occurs in the tourism-related establishments. The indirect effects occur because of the increased purchases of the tourism-related businesses. The direct and indirect effects will have accrued the local income in the form of wages, salaries, profits and rent. The money spent within the local economy will generate additional economic impacts called the induced effect (Bull, 1992 & Fletcher, 1999).
The World Travel and Tourism Council estimates that tourism generates an indirect contribution to local economies equal to 100 % of direct expenditures. However, there are also negative economic impacts such as leakage, infrastructure cost, and an increase in prices (United Nations Environment Programme, 2003). According to the International Air Transport Association (IATA), air transport provides 28 millions jobs worldwide and the total economic impact of air transport on gross world output is of at least US$ 1,360 billion (IATA, 2003a). Furthermore, the organization estimates that the combined direct, indirect and induced employment created at European airports is 4,000 jobs per million passenger served .