Wissenschaftliche und politische Gründe für den Wandel der IPCC-Szenarien

Since its establishment, the Intergovernmental Panel on Climate Change (IPCC) has published three series of emission scenarios that represent the backbone of climate projections. The first IPCC series in 1990 proposed a single business-as-usual emission scenario as a reference, and three intervention scenarios. The third series of scenarios, published in 2000, which is used in the IPCC's recent Fourth Assessment Report, does not include any intervention scenarios but consists of six different reference scenarios. To assess the reasons for these changes, we analyze the changing structure of the IPCC scenarios and the intergovernmental review process they went through. We also compare the scenarios with scenarios from literature. We find that scientific reasons alone cannot explain these changes. During the unification process for the relevant IPCC report, the government representatives involved increased the number of reference scenarios, excluded intervention scenarios, and prevented scenario names that emphasized the interventionist character of those scenarios with low emissions. These findings illustrate difficulties in scenario construction that need to be resolved for the next generation of IPCC scenarios.