How do you carbon offset?

We have a bunch of diseased pine trees. Assuming we don't have enough time to cut them down and burn them in the next 12 months, and that I am unscrupulous, I could sell you carbon credits through one of the bigger exchanges. You would never know, and it would be completely above board.

John Oliver had a particularly depressing segment on this recently.

(Totally off topic, but I'd love to biochar them instead. Using them for lumber and shipping them offsite are non-starters. Any ideas, anyone?)