Analysis Features Integrated Assessment Model from the International Institute for Applied Systems Analysis (IIASA) Two-stage design Short-term (to 2050) Long-term climate goal unknown Achieve a mid-century emissions target Long-term ( ) Climate target is revealed Achieve a 2100 concentration target What range of 2100 targets is achievable? Based on ONeill, Riahi, & Keppo, 2010, Proceedings of the National Academy of Sciences – USA.

CO 2 Emissions Mid-century target analysis A2 Baseline Scenario

Long-term Costs of 2050 Emissions targets 550 CO 2 -eq. ppm Least cost emissions doing too much doing too little 550 ppm becomes unattainable B2 Baseline 550 ppm

Economically less desirable Optimal target Feasibility frontier Not attainable 2 ºC feasibility frontier, B2 reference scenario Based on Forest et al CS PDF B2 Baseline 50% EU goal

Optimal target Feasibility frontier Not attainable 2 ºC feasibility frontier, B2 reference scenario Based on Forest et al CS PDF B2 Baseline 33% Effect of not allowing overshoot best you can do

3 ºC feasibility frontier, B2 reference scenario ~90%

Summary Achieving 2 C target is difficult –Without overshoot, maximum that is technologically feasible is to ensure a 1/3 chance of achieving the goal –Allowing for overshoot, reductions by 2050 may not need to be as stringent as often assumed Specific quantitative results depend on model and assumptions –Energy demand –How fast technologies can be deployed –Climate response to emissions –Participation Qualitative results are robust –Substantial reductions required by 2050 –CCS and negative emissions technologies critical