The first follow-up to my recent post on carbon policy details.
First, a note to non-carbon-wonks: "Additionality" is a term of art in the world of carbon policy. It describes the degree to which a given activity causes additional carbon reductions -- the idea being that we shouldn't pay for carbon reductions that were going to occur anyway. As a fantastic oversimplification, suppose your car broke down and you had to ride your bike to work. The principle of additionality says you shouldn't be paid for the carbon you didn't emit. (You would have ridden anyway -- what choice did you have?) But if there's an increment of money that would tip you over into getting rid of your car and always riding your bike, that's additional.
Theoretically, great idea. Practically? Stupid.
To understand why, go back to the test I posited in my earlier post: Does the metric increase or decrease the rate at which we invest capital to lower GHG emissions?
The answer for additionality is not what you'd expect, for rather subtle reasons.
First off, let's note a couple truths: