"Economic output per ton of CO2" looks like a red herring to me. To borrow a phrase from elsewhere in this thread, the climate doesn't care about economic output.

I'm not saying we won't see costs from decarbonising. We will. I'm saying that worrying too much about the economics will significantly impede the necessary work (as it has done for the past 50 years). It's quite likely that the current financial system is the wrong tool for the job in fixing this problem, now.