The marginal impacts of CO2, CH4 and SF6 emissions

A new version of the PAGE model, PAGE2002, has been used to calculate the marginal impacts of CO2, CH4 and SF 6 emissions based on Scenario A2 of the IPCC. The mean marginal impact of CO2 is found to be US$19 per tonne of carbon (or about US$5 per tonne of CO2), for methane it is US$105 per tonne, and for SF 6 it is US$200,000 per tonne. For each gas, the range between the 5% and 95% points is about an order of magnitude. The climate change impacts of methane are a significant proportion of its market price, and for SF 6 the climate change impacts are much larger than the market price. The economics of schemes to reduce the leakage of SF 6 are transformed once the climate change impacts are properly counted.