According to the barometer of the World Tourism Organization (UNWTO), 980 million tourists traveled around the world in 2011 when they were only 528 million in 1995. UNWTO has recently released its forecast for the next two decades and asserts that the annual growth in the number of international tourists will reach 4 percent. Therefore, there should be around 1.8 billion international tourists in 2030. On the economic side, the tourism industry represents 10.4 percent of the global Gross Domestic Product (UNWTO, 2006) and 8 percent of international employment but, in contrast, tourism alone represents 4-10 percent of the greenhouse gas issued by industry worldwide. It should be noted that 89 percent of CO2 emissions are generated exclusively by public transport between the home and the tourist destination.