Glenn Reynolds has a test to determine the sincerity of those who call for reducing greenhouse gas emissions: Limits on private planes and stretch limos. He writes:
No, seriously. A Gulfstream III releases 10,000 pounds of carbon dioxide an hour. How can we demand "sacrifice" from ordinary Americans when our leaders — including those who call for the sacrifice — are flying in jets like this? If commercial first-class isn't good enough, they should stay home.
Of course, if the United States and other industrialized nations adopted a carbon tax (or its equivalent), those who can afford private jets could likely afford the tax as well.
UPDATE: Glenn Reynolds offers more detail about his views on climate change policy here.