Containing Global Warming after Copenhagen: One-shot and Learning-by Doing Approaches

The perceived success of post Kyoto Protocol mitigation policy largely revolves around the ability of parties to agree to binding targets in 2020 that provide a reasonable likelihood of avoiding 2°C warming. However, neither theory nor practice supports the assumption that a one-shot agreement can deliver such success, nor that it is preferable to a learning-by-doing approach. By contrast, changing information about current and future emissions growth and about evolving climate risks can be used to guide multi-stage processes of adjustment to achieve a given target. To demonstrate this, we examine the effect of changing climate policy on projected emissions over the years 2006–2010. Four cases of projected emissions to 2030 are examined under a consistent set of assumptions: Policy settings in 2006 and 2008, the impact of the Global Financial Crisis (GFC) and commitments given under the Copenhagen Accord. Under 2006 assumptions, median projected warming in 2100 reaches 3.9°C. By late 2009, policy changes are estimated to have reduced the projected atmospheric concentration of Kyoto gases and mean global warming in 2100 by about 15–18%. The impact of the GFC was only about one-quarter of that. Incorporating Copenhagen Accord commitments and a minimum emissions path from 2020 results in projected warming in 2100 of 2.6°C, 30% less than for the 2006 policy settings. Further learning in the short-term, though it may not be easily achieved, may bring the <2°C target within reach. The results provide a strong case for the global community to accept that the learning-by-doing approach is both feasible and potentially effective. The development of policy mechanisms, institutional frameworks and assessment systems that can apply learning in all of these risk domains remains the best hope of achieving the ultimate goals of climate policy.