This way of thinking seems literally insane to me.
These numbers mean pretty much nothing. There is no purpose to arguing whose numbers are right. The problem is what is at risk, and how much it is at risk. People. Places. Beauty. Culture. Safety. Stability. Sanity. Peace.
Quantifying it in GDP gained or lost is so thoroughly senseless that I am rendered speechless. (Well, maybe only for a minute or two. It does make me shake my head a whole lot, though.)