Other measures taken by some tour operators include donations built into their fee structure, with those donations going to local conservation projects. These are laudable - but one wonders how these options can address the link to climate change. Since 1990, CO2 emissions from international air travel have increased by 83 per cent. Between four to nine per cent of the total climate change impacts caused by humans result from air travel.
On the other hand, there is massive criticism of carbon offsets. Some contend it is mere "greenwashing" - not effective, and simply lets people dispense with their guilt, with no real meaningful result. But there has been much effort to address those concerns, and some organizations have gone to great lengths to assure that offsets actually do what is intended. One of the best organizations (The World Land Trust) and resulting actions include: http://www.worldlandtrust.org/
Others links for learning more include:
Gold Standard: http://www.cdmgoldstandard.
Purchasing Carbon Offsets: http://www.davidsuzuki.org/publications/downloads/2009/climate_offset_guide.pdf
The Nature Travel Network and carbon offsets: