Mitigation implications of mid-century targets that preserve long-term climate policy options
Data for download: Spreadsheet
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.
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