Any systematic approach to mitigation should begin with a review of emission intensities, i.e., a systematic assessment of where emissions occur. This is because dozens of smaller changes in the tourism system to reduce emissions will not yield anywhere near as much as one change in the major sources of GHG. As outlined above, aviation is the key sector in emissions, both in terms of current emissions and future growth, and on scales reaching from global, to national, to individual and per trip dimensions. Consequently, any strategy seeking to reduce emissions from tourism should set out with a review of the aviation system and its foundations. The second sector of importance is car travel, accounting for almost the same level of CO2 as aviation, though involving far greater trip numbers. Car use is important to address, however, because growth in emissions from this sector is likely with a rapidly increasing number of people becoming motorized, as well as this sector’s potential to implement technological change leading to considerably reduced specific emissions. With regard to the third most important sub-sector, accommodation accounts for another fifth of emissions and is another sector that is important to address because of the great potential to reduce emissions from buildings. On this basis, an analysis of UNWTOUNEP-WMO (2008), based on scenario modelling, has sought to discuss how emissions from global tourism could be reduced.