Also in this chapter:
Lead authors: Michel den Elzen, Keywan Riahi
Contributing authors: William Hare, Niklas Höhne, Mikiko Kainuma, Jiang Kejun, Chris Taylor, Zhao Xiusheng
This section assesses the potential “emissions gap” between expected emissions based on country pledges and emission levels in 2020 consistent with 2° and 1.5° C limits. For this purpose, we build upon the results in chapters 2 and 3.
As pointed out in Chapter 2, the emission levels consistent with temperature limits depend on the desired likelihood of meeting particular limits, the feasible pace of emission reductions post 2020, and the availability of technology to achieve, for example, negative emissions (Chapter 2, Table 1).
It was explained in Chapter 3 that expected emissions in 2020 depend on whether unconditional or conditional pledges are followed and on the outcome of a number of issues under negotiation, in particular that of LULUCF accounting and surplus emission units (Chapter 3, Figure 2). Given the uncertainty of both expected emissions and emission levels consistent with temperature limits, we do not make a single estimate of the potential gap. Instead, we assess the likely range of the gap based on combinations of assumptions about both expected emissions and emission levels corresponding to temperature targets53.