Because, you know, you can never ask too many questions, I contacted the Union of Concerned Scientists to ask about their Clean Air Act Ticker.
As you might recall, my question was: how can the UCS ticker suggest savings of $1.9T from the Clean Air Act when our GDP is only about $15T/yr?
The short answer is: you can't compare the two.
I talked to climate ecologist Rachel Cleetus at the UCS. She explained that avoided costs do not equate to creating GDP, which makes sense.
It is not easy to put an economic figure on the value that people put on life. You can estimate how much people would spend to avoid certain social and environmental negatives, which is what the EPA's report on air pollution does, and then you can extrapolate.
But, how much would you spend to save your life? All that you have, surely, if you really had to.
So these numbers require some interpretation and thought.