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

  Brian C. O’Neilla,b,1 Keywan Riahib,1 and Ilkka Keppoc

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Mid-century 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 mid-century 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 mid-century conditions are crucial determinants of longer-term climate outcomes, and we identify feasibility thresholds describing conditions that must be met by mid-century in order to keep particular long-term options open.  For example, in order to preserve the technical feasibility of a 50% likelihood of keeping global average temperature at less than 2 C above pre-industrial 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 under such circumstances only barely feasible with known technologies.  Results suggest that a greater focus on mid-century targets could facilitate the development of policies that preserve potentially desirable long-term options.

a National Center for Atmospheric Research, P.O. Box 3000, Boulder, CO, 80307, USA.
b International Institute for Applied Systems Analysis, A-2361 Laxenburg, Austria.
c Energy research Centre of the Netherlands, P.O. Box 56890, 1040 AW Amsterdam, Netherlands.

1Co-corresponding authors. B.C.O and K.R. contributed equally to this work and are listed alphabetically.

Paper submitted to the Proceedings of the National Academy of Sciences – USA April 8, 2009

Dr. Keywan Riahi
International Institute for Applied Systems Analysis (IIASA)
Schlossplatz 1, A-2361 Laxenburg, Austria
Tel: +43 (2236) 807 491    Fax: +43 (2236) 71 313

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