Also in this chapter:
The majority of results in this report show that emissions in 2020 expected from the Copenhagen Accord pledges are higher than emission levels consistent with a “medium” or “likely” chance of staying below 2° C and 1.5° C. At the same time they also show that the range of 2020 emission levels from the Copenhagen Accord pledges tends to be consistent with the IAM pathways that have “likely” temperature increases of 2.5° C to 5° C up to the end of the twenty-first century.
However, this does not mean that a 2° C goal is infeasible. The IAM literature shows that it remains possible to meet the temperature limits reviewed here, but the emission reduction rates required post 2020 are at the high end of what is currently assumed in the IAM literature to be technologically and economically feasible. The IAM literature also shows that options might be limited after 2020: a full range of low-emission technologies would have to be available and broad participation in global efforts to reduce emissions would be needed (Calvin et al. 2009, Clarke et al. 2009, Krey and Riahi 2009, van Vliet et al. 2009). Pathways capable of meeting the 2° C and 1.5° C limits require significant effort to develop technologies for achieving negative CO2 emissions from energy and industry starting shortly after mid-century.
Commencing with such fast rates of emission reduction in 2020 and maintaining them for decades will require significant changes in underlying infrastructure and policy. Thus, if it is desired to meet temperature targets, two things appear to be required: first, countries would have to increase the ambition of their 2020 pledges; and second, society would have to put in place the policy, research, and investment processes to support and sustain such a rapid decline in emissions. Rapid rates of emission reduction will also require sustained global effort and cooperation, since action by only a small subset of countries will not be enough to reach temperature targets (Calvin et al. 2009, Clarke et al. 2009, Clarke and Weyant 2009, Krey and Riahi 2009, van Vliet et al. 2009).
In order to bring emissions in line with IAM pathways that meet a 2° C limit, there is a need to not only implement current pledges fully, but also to raise the ambition of those pledges and lay the groundwork for faster and deeper reductions of post 2020 emissions. Going further in the short term and achieving stronger cuts to lower levels in 2020 would leave open more possibilities to meet temperature limits and would allow more flexibility in choosing a post 2020 pathway for global emissions.