Also in this chapter:

4.3 Findings for 1.5° C

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.

Table 2. The global gap (in GtCO2e per year) between emission levels for staying below 2° C (with a “likely” (greater
than 66 per cent) and a “medium” (50-66 per cent) chance) and expected emissions as a result of the Copenhagen
Accord pledges.
All estimates in this table are derived from the results of chapters 2 and 3. Values in bold
correspond to medians, and numbers in brackets correspond to 20th to 80th percentile of estimates. Numbers in
italics give the adjusted 2020 emission levels for expected emissions from the pledges and emission levels from
the pathways