20


EMISSIONS GAP REPORT 2018 – THE EMISSIONS GAP


and an increase in the upper end of the range for the unconditional and conditional NDC estimates by 2 GtCO2


e and 1 GtCO2 e respectively.


Studies underlying the current policy trajectory scenario and the NDC scenario differ in various ways, such as their treatment of conditional versus unconditional NDCs and their assumptions regarding non-covered sectors and gases. These methodological differences cannot be fully harmonized, which leads to some uncertainty as indicated by the ranges around the median estimates


with the current policy scenario (table 3.1). Some of the new studies included in this year’s assessment have higher NDC estimates, resulting in a slight increase of 1 GtCO2


e and 6 GtCO2 e in the median unconditional NDC estimate


Full implementation of the unconditional and conditional NDCs is estimated to reduce global emissions in 2030 by about 3 GtCO2


e respectively, compared


(see table 3.1 and online appendix A.1). These differences and their implications are further described in online appendix A.2 and in the 2016 Emissions Gap Report (UNEP, 2016), which also provides a more complete discussion of the different types of scenarios.


The major change compared with the 2017 Emissions Gap Report is in the assessment of 2030 GHG emission levels consistent with limiting global warming to below 2°C and lower. As discussed in section 3.2, the 2018 assessment draws on numerous new 1.5°C and 2°C-consistent least-cost emissions pathways that have become available in the context of the IPCC Special Report (Huppmann et al., 2018a, 2018b). Furthermore, the assessment adopts a new methodology, which groups pathways under three temperature scenarios based on their cumulative CO2


emissions. These updates result in target emission levels for 2030 that


Figure 3.1: Global greenhouse gas emissions under different scenarios and the emissions gap in 2030 (median estimate and 10th


to 90th percentile range).


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