A MODEL-BASED APPROACH TO THE CALCULATION OF GLOBAL WARMING POTENTIALS (GWP)

The Global Warming Potential (GWP) of greenhouse gas emissions can be defined as a greenhouse pendant to the Ozone Depleting Potential (ODP). Global Warming Potentials are calculated for the most important greenhouse gases (CO2, CH4, CO, N2O, CFC-11, CFC-12, CFC-13, CFC-14, CFC-113, CFC-114, CFC-115, CFC-116, CF3Br, CCl4, CH3CCl3, and HCFC-22) and eight potential CFC substitutes using the integrated climate assessment model IMAGE. Two different methods are presented for the calculation of GWP values using IMAGE: one that generates equivalent pulses for all greenhouse gases, and an iterative trace-back method which calculates the different pulses required to achieve an identical global temperature increase for all greenhouse gases. In addition the influence of the emission scenario used is tested when determining GWPs; it is demonstrated that GWPs are indeed scenario-dependent, so the choice of the underlying emission scenario is important. Finally, the GWPs calculated using these methods are compared with GWPs that have been published previously. It appears that our GWP estimates are substantially higher than the IPCC estimates, which can be explained by the fact that our carbon cycle model has a balanced global carbon budget. This results in lower projections of future atmospheric carbon dioxide compared with the IPCC projections.