16


EMISSIONS GAP REPORT 2018 – THE EMISSIONS GAP


Chapter 3. The emissions gap


Lead authors: Gunnar Luderer (Potsdam Institute for Climate Impact Research), Joeri Rogelj (Imperial College London/ International Institute for Applied System Analysis), Michel den Elzen (PBL Netherlands Environmental Assessment Agency), Jiang Kejun (Energy Research Institute, China)


Contributing authors: Daniel Huppmann (International Institute for Applied Systems Analysis)


3.1 Introduction


This chapter presents an update of the emissions gap in 2030. In line with previous reports, the emissions gap is defined as the difference between where global greenhouse gas (GHG) emissions are heading under the current Nationally Determined Contributions (NDCs) and where science indicates emissions should be in 2030 to be on a least-cost path towards limiting warming to below 2°C or further to 1.5°C. The 2018 assessment draws on several new studies that present updated NDC estimates and additional low emission scenarios in line with achieving the climate objective of the Paris Agreement.


The chapter starts with an introduction to the scenarios that have been used and the updates made (section 3.2). This is followed by an updated assessment of the emissions gap in 2030 (section 3.3), which builds on an updated assessment of emission levels in 2030, under current policies, NDCs and emission levels consistent with least-cost mitigation pathways to below 2°C to 1.5°C. The chapter then provides an update on the implications of temperatures projections anticipated under current NDCs (section 3.4), concluding with an analysis of the effects of higher or lower emissions in 2030 (section 3.5)


3.2 Scenarios considered and updates made


The emissions gap assessment draws on three main types of scenarios of total global GHG emissions in the future: reference scenarios, NDC scenarios and least-cost mitigation scenarios consistent with specific temperature targets (see UNEP, 2016, 2017). Each of these scenarios and the updates made since the 2017 Emissions Gap Report are described below.


3.2.1 Reference scenarios and updates


Reference scenarios are useful benchmarks against which progress in emission reductions can be tracked. Two reference scenarios are considered: the no-policy baseline and current policy scenarios. The no-policy baseline scenario explores the trend of global GHG emissions in the absence of climate policies post-


2005. It is based on mean projections of 179 baseline scenarios assessed in the 5th


Assessment Report of


the Intergovernmental Panel on Climate Change (IPCC) (Clarke et al., 2014). Recently, new no-policy baselines have been published, though these have not resulted in significant changes to the no-policy baseline scenario estimates (Riahi et al., 2017; Luderer et al., 2018).


The current policy scenario estimates future global GHG emissions, assuming that all currently adopted and implemented policies (defined as legislative decisions, executive orders or equivalent) have been realized and that no additional measures are to be undertaken. The scenario is based on the country analyses in chapter 2 and updated global analyses that use new data from eight modelling groups. These include updated analyses from the four modelling groups considered in the 2017 Emissions Gap Report (UNEP, 2017), namely, the Climate Action Tracker (CAT, 2018), the Joint Research Centre (Kitous et al., 2017), PBL Netherlands Environmental Assessment Agency (Kuramochi et al., 2017; PBL, 2018) and the International Energy Agency (IEA, 2017).


3.2.2 NDC scenarios and updates


NDC scenarios are used to estimate what the total global GHG emissions would be in 2030 if countries fully implemented their pledged contributions. Following previous Emissions Gap Reports, two NDC scenarios are considered: the unconditional and conditional NDC scenarios.


Under the unconditional NDC scenario, it is assumed that countries only implement mitigation-related actions of their NDCs that have no conditions attached. Countries that do not have an NDC or have only included a conditional target are assumed to follow a current policy scenario instead. Under the conditional NDC scenario, it is assumed that countries implement both conditional and unconditional mitigation actions of their NDCs. Countries without an NDC are assumed to follow a current policy scenario and those without a conditional target follow the unconditional scenario.


Global emission projections from 15 modelling groups are considered for the two NDC scenarios. These


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47  |  Page 48  |  Page 49  |  Page 50  |  Page 51  |  Page 52  |  Page 53  |  Page 54  |  Page 55  |  Page 56  |  Page 57  |  Page 58  |  Page 59  |  Page 60  |  Page 61  |  Page 62  |  Page 63  |  Page 64  |  Page 65  |  Page 66  |  Page 67  |  Page 68  |  Page 69  |  Page 70  |  Page 71  |  Page 72  |  Page 73  |  Page 74  |  Page 75  |  Page 76  |  Page 77  |  Page 78  |  Page 79  |  Page 80  |  Page 81  |  Page 82  |  Page 83  |  Page 84  |  Page 85  |  Page 86  |  Page 87  |  Page 88  |  Page 89  |  Page 90  |  Page 91  |  Page 92  |  Page 93  |  Page 94  |  Page 95  |  Page 96  |  Page 97  |  Page 98  |  Page 99  |  Page 100  |  Page 101  |  Page 102  |  Page 103  |  Page 104  |  Page 105  |  Page 106  |  Page 107  |  Page 108  |  Page 109  |  Page 110  |  Page 111  |  Page 112