21
differ from the ranges assessed in the 2017 report. Table 3.1 shows that in the below 2.0°C scenario (about 66 percent probability), which is consistent with maximum cumulative emissions of 900–1,300 GtCO2 GHG emission levels for 2030 are 40 GtCO2 38–45 GtCO2
, e (range of
warming below 1.8°C with about 66 percent probability, GHG emission levels for 2030 are 34 GtCO2
30–40 GtCO2 2017 of 36 GtCO2
based on pathways where cumulated maximum CO2 emissions from 2018 are below 600 GtCO2 levels in 2030 are as low as 24 GtCO2 GtCO2
e). This is 12 GtCO2
because many recent studies assume that less negative emissions will be available over the course of this century, thus requiring steeper emission reductions in the next decades to keep peak warming as low as possible. The inclusion of pathways consistent with keeping global warming to below 1.8°C, combined with the indication of temperature outcomes for about a 50 percent, 90 percent and 66 percent probability, allow for a more nuanced interpretation and discussion of what ‘well below 2°C’ means and implies in terms of emission reductions required.
e (range of 32–38 GtCO2 with the below 2°C scenario. This is about 2 GtCO2 e (range of 12–17 GtCO2
The emissions gap between estimated total global emissions in 2030 under the NDC scenarios and pathways limiting warming to below 2°C and 1.5°C is illustrated in figure 3.1, where the no-policy and current policy scenarios are also included. Full implementation of unconditional NDCs is estimated to result in a gap of 15 GtCO2
e) in 2030 compared e
(range of 28–34 GtCO2
e. The emissions gap between unconditional NDCs and below 1.5°C pathways is about 32 GtCO2
e
than assessed in the 2017 report, due to the lower 1.5°C scenario estimates as explained above. Considering the full implementation of both unconditional and conditional NDCs would reduce this gap by roughly 3 GtCO2
e). This is about 13 GtCO2 e.
of current policies. As the emissions gap assessment shows, reductions that are roughly 2 to 3 times higher are needed to bridge the gap between conditional NDCs and 2°C pathways, and five times higher to align emissions with 1.5°C pathways.
In summary, the assessment amplifies concerns regarding both ambition and action compared with previous Emissions Gap Reports. According to the current policy and NDC scenarios, global emissions are not estimated to peak by 2030, let alone by 2020. The NDCs are estimated to reduce global emissions in 2030 by a maximum 6 GtCO2
e compared with a continuation
higher than the gap assessed in the 2017 report, due to the lower 2°C scenario estimate. If the conditional NDCs are also fully implemented, the gap reduces by about 2 GtCO2
e higher
e). For the below 1.5°C in 2100 scenario, , emission
e (range of 22–30
e lower than the estimate in e), mainly
estimates but well within the reported uncertainty range. For pathways with maximum cumulative emissions of 600–900 GtCO2
e). This is around 2 GtCO2
, which is consistent with keeping global e (range of
e lower than 2017
3.4 Temperature implications of the NDCs
The implications for global warming by the end of the century can be estimated based on the 2030 level of GHG emissions resulting from full implementation of the NDCs. The Emissions Gap Reports use a method that builds on information from scenarios available in the peer-reviewed literature. Such scenarios provide internally consistent long-term emission projections and relate 2030 GHG emission levels to temperature outcomes throughout the 21st
century (Rogelj et al.,
2016a). The method used in these reports has been assessed in a recent study (Jeffery et al., 2018) to provide consistent and useful results for a wide range of emissions reduction levels in 2030, in contrast to some of the other methods found in the literature consulted.
Assuming that climate action continues consistently throughout the 21st
century, implementing the
2100, temperatures are further projected to increase thereafter. Full implementation of both unconditional and conditional NDCs would reduce these estimates by 0.2°C in 2100. These projections are identical to those made in 2017, within rounding precision.
unconditional NDCs would lead to a mean global temperature of around 3.2°C (with a range of 2.9–3.4°C), relative to pre-industrial levels by 2100. Since these projections do not reach net zero CO2
emissions by 3.5 Implications of 2030 emission levels
The large ranges in least-cost 2030 global GHG emissions reported in table 3.1 for limiting warming to below 2°C or 1.5°C not only reflect variations between models, but also differences in societal choices that should be made to achieve desired climate outcomes. Such outcomes may include deciding the degree to which it is acceptable to rely on large-scale CDR after 2050, how mitigation action should be spread over time or what an acceptable level of burden is for future generations. Recent studies allow these choices to be better understood by illustrating the implications associated with aiming to achieve the higher or lower end of the identified ranges, or with missing them altogether. The recently approved IPCC Special Report on Global Warming of 1.5°C points out that the global emissions outcome from the aggregate effect of the NDCs is too high to prevent exceedance of the 1.5°C threshold (IPCC, 2018; Rogelj et al., 2018). Here, the focus is on implications of 2030 emission level choices for (1) the future reliance and scale of CDR; (2) the simultaneous achievement of other sustainability objectives; and (3) lock-in of carbon-intensive infrastructure that makes future emission reductions more difficult.
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