"The other reason to love this story is that it is about getting paid not to do things. That is always complicated. If you are paid to do things, it is relatively easy to measure how much you did and how much you should get paid. If I want you to cut down trees for my sawmill, we might agree on a price of $5 per tree. You will cut down the trees and deliver them to me, and I will count them. If you deliver 100 trees then I’ll pay you $500.

"But if I want you not to cut down trees for my carbon capture program, it is harder to measure how many trees you didn’t cut down. Just sitting here right now, typing this column on my computer, I have cut down zero trees,[1] which means in theory that there are absolutely billions of trees that I have not cut down. Where is my check? A landowner might have planned to cut down only a few trees this year, but she will have incentives to say “I was planning to cut down all my trees,” in order to get paid for not cutting down all of them. She might have trees that are impossibly un-economic to cut down, but it’s easy enough for her not to cut them down.

"Similarly, if I agree to buy 100 trees from you, and you sell me the trees, you can’t sell them to anyone else: I have the trees. If I agree to pay you not to cut down 100 trees, though, what’s to stop you from getting paid by someone else not to cut down the same trees? The trees stay there; you can sell the concept of them staying there as many times as you like."