The carbon credit commodity market will be the next dot com bubble and Enron all rolled into one. Someday someone will wake up and say, "Hey! Show me all the research and benefits from my purchase of carbon credits. Show me the thousands of trees I planted, and show me exactly how much cleaner I have made the Earth."
And the carbon barons will quickly get one-way tickets to elsewhere, with all that carbon money safely in offshore accounts, and...no forests of trees and no measurable benefits will be found. At that point, you won't be able to sell a carbon credit for a penny.