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Monday, January 18, 2010

Brian O'Neill, Keywan Riahi & Ilkka Keppo, PNAS (January 13, 2010), Mitigation implications of midcentury targets that preserve long-term climate policy options

Proceedings of the National Academy of Sciences, published online before print January 13, 2010; doi: 10.1073/pnas.0903797106

Mitigation implications of midcentury targets that preserve long-term climate policy options

Brian O'Neill* (National Center for Atmospheric Research, P.O. Box 3000, Boulder, CO 80307, U.S.A., and the International Institute for Applied Systems Analysis (IIASA), A-2361 Laxenburg, Austria), Keywan Riahi* (International Institute for Applied Systems Analysis (IIASA), A-2361 Laxenburg, Austria) and Ilkka Keppo (Energy Research Center of the Netherlands, P.O. Box 56890, 1040 AW Amsterdam, Netherlands)

Edited by Stephen H. Schneider, Stanford University, Stanford, CA, and approved October 23, 2009 (received for review April 8, 2009).


Midcentury targets have been proposed as a guide to climate change policy that can link long-term goals to shorter-term actions. However no explicit mitigation analyses have been carried out of the relationship between midcentury conditions and longer-term outcomes. Here we use an integrated assessment modeling framework with a detailed representation of the energy sector to examine the dependence of climate change outcomes in 2100 on emissions levels, atmospheric concentrations, and technology characteristics in 2050. We find that midcentury conditions are crucial determinants of longer-term climate outcomes, and we identify feasibility thresholds describing conditions that must be met by midcentury to keep particular long-term options open. For example, to preserve the technical feasibility of a 50% likelihood of keeping global average temperature at < 2 °C above preindustrial in 2100, global emissions must be reduced by about 20% below 2000 levels by 2050. Results are sensitive to several assumptions, including the nature of future socio-economic development. In a scenario with high demand for energy and land, being below 2 °C with 50% likelihood requires a 50% reduction in emissions below 2000 levels by 2050, which is only barely feasible with known technologies in that scenario. Results suggest that a greater focus on mid-century targets could facilitate the development of policies that preserve potentially desirable long-term options.

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