This article examines how to account for the welfare effects of carbon dioxide emissions, using the historical experiences of Britain and the USA from the onset of the industrial revolution to the present. While a single country might isolate itself from the detrimental effects of global warming in the short run, in the long all countries are unable to free ride. Thus, we support the use of a single global price for carbon dioxide emissions. The calculated price should decrease as we move back in time to take into account that carbon dioxide is a stock pollutant, and that one unit added to the present large stock is likely to cause more damage than a unit emitted under the lower concentration levels in the past. We incorporate the annual costs of British and US carbon emissions into genuine savings, and calculate the accumulated costs of their carbon dioxide emissions. Enlarging the scope and calculating the cumulative cost of carbon dioxide from the four largest emitters gives new insights into the question of who is responsible for climate change.