Will sustainability fly : aviation fuel options in a low carbon world While international negotiations to reduce greenhouse gas (GHG) emissions have been less than satisfactory there is a presumption that a significant level of multi lateral commitment will be realized at some point. International air and marine travel have been left to one side in past talks because the pursuit of agreement proceeds on the basis of commitment by sovereign nations and the effects of these specific commercial activities are by their nature difficult to corral and assign to specific national jurisdictions. However air travel is increasing and unless something is done emissions from this segment of our world economy will form a progressively larger percentage of the total especially as emissions fall in other activities.