Also in this chapter:
There is no emission pathway in the assessed IAM literature of Chapter 2 that achieves the 1.5° C limit with a “likely” (greater than 66 per cent) chance and only one study in this literature depicts an emission pathway consistent with a medium (50-66 per cent) chance of meeting the 1.5° C limit (Magné et al. 2010). The IAM pathways assessed that meet the 2° C limit with a “likely” chance suggest, however, that after a small (0.1-0.2° C) transient overshoot of the 1.5° C target, the temperature increase by the end of the twenty-first century could drop below 1.5° C, but with a lower probability. These pathways reach the 1.5° C target in the long-term with a median probability of 30 per cent (range of 27-35 per cent).
Reaching 1.5° C with these lower probabilities would thus leave a similar emissions gap in 2020 as the one for a “likely” chance for 2° C. However, having a “likely” chance of reaching the 1.5° C target would require higher rates of emission reductions after 2020 (and correspondingly high rates of technological development and deployment) than those reported in the IAM literature.