A Back-of-the-Envelope Calculation of The Social Cost of Carbon

If we 1) assume that AGW causes the ice caps to melt; 2) the resulting flood displaces 10% of the world population; 3) the cost of relocation per person is of the same order of magnitude as the per capita GDP; 4) the appropriate discount rate is about the same as the GDP growth rate (Piketty thinks it's more); 5) all this happens over the course of the next century, then total cost per ton of carbon is about the world GDP divided by the annual carbon emissions divided by 1000. The world GDP is $84.97 trillion. The annual CO₂ emissions are 31,350,455 thousands of tonnes. Since 12 tonnes of carbon produces 44 tonnes of CO₂, the social cost of carbon is $9.94 per tonne of carbon.

Yes. I've made several simplifying assumptions … starting with the assumption of solar or other nuclear hasn't made fossil fuels obsolete and continuing with the assumption that many places won't be improved by the absence of blizzards and assuming that increased plant growth won't absorb the excess CO₂… On the other hand, this is a starting point. It shows that we can face facts without being hysterical and that the people who are getting hysterical are emitting the highly toxic pollution known as bulshytt.

On the gripping hand, a back-of-the-envelope calculation also shows you can be run over by a cupcake.