GHG mitigation potentials in Annex I countries Comparison of model estimates for 2020 Markus Amann

Interim Reports on work of the International Institute for Applied Systems Analysis receive only limited review. Views or opinions expressed herein do not necessarily represent those of the Institute, its National Member Organizations, or other organizations supporting the work. Abstract Robust quantification of the future potentials and costs for mitigating greenhouse gases in different countries could provide important information to the current negotiations on a post-2012 climate agreement. However, such information is not readily available from statistical sources, but requires the use of complex models that combine economic, technological and social aspects. In March 2009, the International Institute for Applied Systems Analysis (IIASA) invited leading modelling teams to a comparison of available model estimates of GHG mitigation potentials and costs in the Annex I countries for the year 2020. Eight modelling teams provided input to this comparison exercise. Although at face value estimates of mitigation potentials and costs show wide variation across models, differences (i) in assumptions on the baseline economic development, (ii) in the definition of which mitigation measures are considered part of the baseline, and (iii) in the time window assumed for the implementation of mitigation measures explain much of the variation in model results. The paper presents a checklist of factors that need to be considered when interpreting model results. Once corrected for these key factors, two clusters of cost curves emerge for the year 2020: Models that include consumer demand changes and macroeconomic feedbacks agree on a mitigation potential of up to 40% reduction below 2005 levels (that is approximately 45% below the 1990 level) for total Annex I emissions in 2020 for a carbon price of 50 to 150 US-$/tCO 2. Bottom-up models that restrict their analysis to technical measures show only half of this potential. The model intercomparison demonstrates that future economic development has a strong impact on the efforts necessary to achieve given emission reduction levels. Any delay in the start of implementation of mitigation measures will reduce the mitigation potential that is achievable in the near term and increase the costs. The introduction of measures that mobilize demand adjustments through structural or behavioural changes may increase the short-term mitigation potential significantly. v Acknowledgments The authors wish to express their sincere thanks to their colleagues from modelling teams that have provided results to the model intercomparison and offered thoughtful proposals for the interpretation of data: The work of Markus Amann and Peter Rafaj …