Editing IPCC:AR6/WGIII/Chapter-4 (section)

=== Cross-Chapter Box 4 | Comparison of NDCs and current policies with the 2030 GHG Emissions from Long-term Temperature Pathways ===

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'''Authors:''' Edward Byers (Austria/Ireland), Michel den Elzen (the Netherlands), Céline Guivarch (France), Volker Krey (Germany/Austria), Elmar Kriegler (Germany), Franck Lecocq (France), Keywan Riahi (Austria), Harald Winkler (South Africa)

Introduction

The Paris Agreement (PA) sets a long-term goal of holding the increase of global average temperature to ‘well below 2°C above pre-industrial levels’ and pursuing efforts to limit the temperature increase to 1.5°C above pre-industrial levels. This is underpinned by the ‘aim to reach global peaking of greenhouse gas emissions as soon as possible’ and ‘achieve a balance between anthropogenic emissions by sources and removals by sinks of GHG in the second half of this century’ ( [[#UNFCCC--2015a|UNFCCC 2015a]] ). The PA adopts a bottom-up approach in which countries determine their contribution to reach the PA’s long-term goal. These national targets, plans and measures are called ‘nationally determined contributions’ or NDCs.

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[[File:a62e9a5f3b9801a531b2da5994774242 IPCC_AR6_WGIII_CCBox_4_Figure_1.png]]

'''Cross-Chapter Box 4, Figure 1:''' '''Global GHG emissions of modelled pathways (funnels in Panel a, and associated bars in Panels b, c, d) and projected emission outcomes from near-term policy assessments for 2030 (Panel b).'''

'''Panel a''' shows global GHG emissions over 2015–2050 for four types of assessed modelled global pathways:

'''–''' Trend from implemented policies: Pathways with projected near-term GHG emissions in line with policies implemented until the end of 2020 and extended with comparable ambition levels beyond 2030 (29 scenarios across categories C5–C7, Table SPM.2).

'''–''' Limit to 2°C (&gt;67%) or return warming to 1.5°C (&gt;50%) after a high overshoot, NDCs until 2030: Pathways with GHG emissions until 2030 associated with the implementation of NDCs announced prior to COP26, followed by accelerated emissions reductions likely to limit warming to 2°C (C3b, Table SPM.2) or to return warming to 1.5°C with a probability of 50% or greater after high overshoot (subset of 42 scenarios from C2, Table SPM.2).

'''–''' Limit to 2°C (&gt;67%) with immediate action: Pathways that limit warming to 2°C (&gt;67%) with immediate action after 2020 (C3a, Table SPM.2).

'''–''' Limit to 1.5°C (&gt;50%) with no or limited overshoot: Pathways limiting warming to 1.5°C with no or limited overshoot (C1, Table SPM.2 C1). All these pathways assume immediate action after 2020.

Past GHG emissions for 2010–2015 used to project global warming outcomes of the modelled pathways are shown by a black line [[#footnote-002|4]] and past global GHG emissions in 2015 and 2019 as assessed in [[IPCC:Wg3:Chapter:Chapter-2|Chapter 2]] are shown by whiskers.

'''Panels b, c and d''' show snapshots of the GHG emission ranges of the modelled pathways in 2030, 2050, and 2100, respectively. Panel b also shows projected emissions outcomes from near-term policy assessments in 2030 from Chapter 4.2 (Tables 4.2 and 4.3; median and full range). GHG emissions are in CO 2 -equivalent using GWP100 from AR6 WGI. {3.5, 4.2, Table 4.2, Table 4.3, Cross-Chapter Box 4 in Chapter 4}

The NDCs are a central instrument of the PA to achieve its long-term goal. It thus combines a global goal with a country-driven (bottom-up) instrument to a hybrid climate policy architecture to strengthen the global response to climate change. All signatory countries committed to communicating nationally determined contributions including mitigation targets, every five years. While the NDCs mostly state targets, countries are also obliged to pursue domestic mitigation measures to achieve the objectives. The literature examines the emissions outcome of the range of policies implemented to reach these targets.

Emissions gap

A comparison between the projected emission outcomes of current policies, the NDCs (which include unconditional and conditional elements, Section 4.2.1) and mitigation pathways acting immediately, i.e. from 2020 onwards, on reaching different temperature goals in the long-term ( [[IPCC:Wg3:Chapter:Chapter-3#3.3.3|Section 3.3.3]] ) allows identifying different ‘emission gaps’ in 2030 (Cross-Chapter Box 4, Figure 1). First, the implementation gap between ‘current policies’ and unconditional and conditional NDCs is estimated to be around 4 and 7 GtCO 2 -eq in 2030, respectively (Section 4.2.2 and Tables 4.2 and 4.3). Second, the comparison of unconditional (conditional) NDCs and long-term mitigation pathways that limit warming to 2°C (&gt;67%) or lower gives rise to a 2030 median emissions gap of 19–26 GtCO 2 -eq (16–23 GtCO 2 -eq) for limiting end-of-century warming to 1.5°C (&gt;50%) with no or limited overshoot and 10–16 GtCO 2 -eq (6–14 GtCO 2 -eq) for limiting warming to 2°C (&gt;67%). [[#footnote-001|5]] GHG emissions of NDCs are broadly consistent with 2030 emission levels of cost-effective long-term pathways staying below 2.5°C (scenarios category C5, Table 3.2, Chapter 3).

Other ‘gap indicators’

Beyond the quantification of different GHG emissions gaps, there is an emerging literature that identifies gaps between current policies, NDCs and long-term temperature in terms of other indicators, including for example the deployment of low-carbon energy sources, energy efficiency improvements, fossil fuel production levels or investments into mitigation measures ( [[#Roelfsema--2020|Roelfsema et al. 2020]] ; [[#McCollum--2018|McCollum et al. 2018]] ; [[#SEI--2020|SEI et al. 2020]] ).

A 2030 gap in the contribution of low-carbon energy sources to the energy mix in 2030 between current policies and cost-effective long-term temperature pathways is calculated to be around 7percentage-points (2°C) and 13percentage-points (1.5°C) by Roelfsema et al. ( [[#Roelfsema--2020|Roelfsema et al. 2020]] ). The same authors estimate an energy intensity improvement gap 10% and 18% for 2030 between current policies pathways and 2°C and 1.5°C pathways, respectively. [[#SEI--2020|SEI et al. (2020)]] estimates the ‘fossil fuel production gap’, by which they mean ‘the level of countries’ planned fossil fuel production expressed in their carbon content to be 120% and 50% higher compared to the fossil fuel production consistent with 1.5°C and 2°C pathways, respectively, as assessed in IPCC SR1.5 ( [[#Rogelj--2018a|Rogelj et al. 2018a]] ).

Cross-Chapter Box 4

The methodology used for this estimation is very similar to how emissions gaps are derived (SEI et al. 2019). The gap of global annual average investments in low-carbon energy and energy efficiency in 2030 between following current policy on the one hand and achieving the NDCs, the 2°C and 1.5°C targets on the other hand, is estimated to be approximately USD 130, 320, or 480 billion per year ( [[#McCollum--2018|McCollum et al. 2018]] ).

It is important to note that such comparisons are less straight forward as the link between long-term temperature goals and these indicators is less pronounced compared to the emission levels themselves; they are therefore associated with greater uncertainty compared to the emissions gap.

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