> However, come to think of it, one might want to give everyone some carbon credit or travel points, and then develop a market in it.

This already exists, but the problem is that carbon credits are nearly impossible to regulate (it's very hard to prove that some carbon-reducing initiative isn't counted toward two distinct carbon credit programs or that the carbon is even reduced as promised). It's hard to do the accounting correctly for honest participants, which pretty much guarantees fraud among less honest participants.