Updated with GISS Global Temperature and the Charney estimates at bottom:
Once the minions of the Great and Power Carbon spread their faith to the economic community, the finest Economists the world has to offer discuss the discount rate that should be justified for saving the world from the greatest peril current rattling around in the minds of the minions. If "sensitivity" is greater than 3C it will cost trillions of US dollars to save the world, over $30 per ton of Carbon must be charged. If "Sensitivity" is approximately 1.6 C, the world can eke by on a measly trillion or so with Carbon taxed at about $3 per ton. If "Sensitivity" is less than 1, the whole Great and Powerful Carbon Crisis should have never existed.