Mitigation Pathways Compatible with 1.5°C in the Context 2 of Sustainable Development Coordinating Lead Authors: Joeri Rogelj (Austria/Belgium), Drew Shindell (USA), Kejun Jiang (China) Lead Authors: Solomone Fifita (Fiji), Piers Forster (UK), Veronika Ginzburg (Russia), Collins Handa (Kenya), Haroon Kheshgi (USA), Shigeki Kobayashi (Japan), Elmar Kriegler (Germany), Luis Mundaca (Sweden/Chile), Roland Séférian (France), Maria Virginia Vilariño (Argentina) Contributing Authors: Katherine Calvin (USA), Joana Correia de Oliveira de Portugal Pereira (UK/Portugal), Oreane Edelenbosch (Netherlands/Italy), Johannes Emmerling (Italy/Germany), Sabine Fuss (Germany), Thomas Gasser (Austria/France), Nathan Gillett (Canada), Chenmin He (China), Edgar Hertwich (USA/Austria), Lena Höglund-Isaksson (Austria/Sweden), Daniel Huppmann (Austria), Gunnar Luderer (Germany), Anil Markandya (Spain/UK), David L. McCollum (USA/Austria), Malte Meinshausen (Australia/Germany), Richard Millar (UK), Alexander Popp (Germany), Pallav Purohit (Austria/India), Keywan Riahi (Austria), Aurélien Ribes (France), Harry Saunders (Canada/USA), Christina Schädel (USA/Switzerland), Chris Smith (UK), Pete Smith (UK), Evelina Trutnevyte (Switzerland/Lithuania), Yang Xiu (China), Wenji Zhou (Austria/China), Kirsten Zickfeld (Canada/Germany) Chapter Scientists: Daniel Huppmann (Austria), Chris Smith (UK) Review Editors: Greg Flato (Canada), Jan Fuglestvedt (Norway), Rachid Mrabet (Morocco), Roberto Schaeffer (Brazil) This chapter should be cited as: Rogelj, J., D. Shindell, K. Jiang, S. Fifita, P. Forster, V. Ginzburg, C. Handa, H. Kheshgi, S. Kobayashi, E. Kriegler, L. Mundaca, R. Séférian, and M.V. Vilariño, 2018: Mitigation Pathways Compatible with 1.5°C in the Context of Sustainable Development. In: Global Warming of 1.5°C. An IPCC Special Report on the impacts of global warming of 1.5°C above pre-industrial levels and related global greenhouse gas emission pathways, in the context of strengthening the global response to the threat of climate change, sustainable development, and efforts to eradicate poverty [Masson-Delmotte, V., P. Zhai, H.-O. Pörtner, D. Roberts, J. Skea, P.R. Shukla, A. Pirani, W. Moufouma-Okia, C. Péan, R. Pidcock, S. Connors, J.B.R. Matthews, Y. Chen, X. Zhou, M.I. Gomis, E. Lonnoy, T. Maycock, M. Tignor, and T. Waterfield (eds.)]. In Press. 93 Chapter 2 Mitigation Pathways Compatible with 1.5°C in the Context of Sustainable Development Table of Contents Executive Summary .....................................................................95 2.6 Knowledge Gaps ...........................................................157 2.6.1 Geophysical Understanding........................................157 2.1 Introduction to Mitigation Pathways and the Sustainable Development Context ....................98 2.6.2 Integrated Assessment Approaches ............................158 2.1.1 Mitigation Pathways Consistent with 1.5°C .................98 2.6.3 Carbon Dioxide Removal (CDR) ..................................158 2.1.2 The Use of Scenarios ...................................................98 2.1.3 New Scenario Information since AR5 ...........................99 2.1.4 Utility of Integrated Assessment Models (IAMs) Frequently Asked Questions in the Context of this Report ......................................100 FAQ 2.1: What Kind of Pathways Limit Warming to 1.5°C and are we on Track? ...........................................159 2 2.2 Geophysical Relationships and Constraints .........101 FAQ 2.2: What do Energy Supply and Demand 2.2.1 Geophysical Characteristics of Mitigation Pathways ..101 have to do with Limiting Warming to 1.5°C? .....................161 2.2.2 The Remaining 1.5°C Carbon Budget .........................104 2.3 Overview of 1.5°C Mitigation Pathways ...............108 References ...................................................................................163 2.3.1 Range of Assumptions Underlying 1.5°C Pathways ....109 2.3.2 Key Characteristics of 1.5°C Pathways .......................112 2.3.3 Emissions Evolution in 1.5°C Pathways ......................115 2.3.4 CDR in 1.5°C Pathways ..............................................118 Box 2.1: Bioenergy and BECCS Deployment in Integrated Assessment Modelling ....................................124 2.3.5 Implications of Near-Term Action in 1.5°C Pathways ..126 2.4 Disentangling the Whole-System Transformation ..............................................................129 2.4.1 Energy System Transformation ...................................129 2.4.2 Energy Supply .............................................................130 2.4.3 Energy End-Use Sectors ..............................................136 2.4.4 Land-Use Transitions and Changes in the Agricultural Sector ................................................144 2.5 Challenges, Opportunities and Co-Impacts of Transformative Mitigation Pathways ................148 2.5.1 Policy Frameworks and Enabling Conditions ..............148 Cross-Chapter Box 5 | Economics of 1.5°C Pathways and the Social Cost of Carbon ...............................................150 2.5.2 Economic and Investment Implications of 1.5°C Pathways ....................................................................152 2.5.3 Sustainable Development Features of 1.5°C Pathways ......................................................156 94 Mitigation Pathways Compatible with 1.5°C in the Context of Sustainable Development Chapter 2 Executive Summary Limiting warming to 1.5°C depends on greenhouse gas (GHG) emissions over the next decades, where lower GHG emissions in 2030 lead to a higher chance of keeping peak warming to 1.5°C This chapter assesses mitigation pathways consistent with limiting (high confidence). Available pathways that aim for no or limited (less warming to 1.5°C above pre-industrial levels. In doing so, it explores than 0.1°C) overshoot of 1.5°C keep GHG emissions in 2030 to 25–30 −1 the following key questions: What role do CO2 and non-CO2 emissions GtCO2e yr in 2030 (interquartile range). This contrasts with median −1 play? {2.2, 2.3, 2.4, 2.6} To what extent do 1.5°C pathways involve estimates for current unconditional NDCs of 52–58 GtCO2e yr in overshooting and returning below 1.5°C during the 21st century? {2.2, 2030. Pathways that aim for limiting warming to 1.5°C by 2100 after 2.3} What are the implications for transitions in energy, land use and a temporary temperature overshoot rely on large-scale deployment sustainable development? {2.3, 2.4, 2.5} How do policy frameworks of carbon dioxide removal (CDR) measures, which are uncertain and affect the ability to limit warming to 1.5°C? {2.3, 2.5} What are the entail clear risks. In model pathways with no or limited overshoot of associated knowledge gaps? {2.6} 1.5°C, global net anthropogenic CO2 emissions decline by about 45% from 2010 levels by 2030 (40–60% interquartile range), reaching net The assessed pathways describe integrated, quantitative zero around 2050 (2045–2055 interquartile range). For limiting global evolutions of all emissions over the 21st century associated warming to below 2°C with at least 66% probability CO emissions 2 2 with global energy and land use and the world economy. The are projected to decline by about 25% by 2030 in most pathways (10– assessment is contingent upon available integrated assessment 30% interquartile range) and reach net zero around 2070 (2065–2080 literature and model assumptions, and is complemented by other interquartile range).1 {2.2, 2.3.3, 2.3.5, 2.5.3, Cross-Chapter Boxes 6 in studies with different scope, for example, those focusing on individual Chapter 3 and 9 in Chapter 4, 4.3.7} sectors. In recent years, integrated mitigation studies have improved the characterizations of mitigation pathways. However, limitations Limiting warming to 1.5°C implies reaching net zero CO2 remain, as climate damages, avoided impacts, or societal co-benefits emissions globally around 2050 and concurrent deep reductions of the modelled transformations remain largely unaccounted for, while in emissions of non-CO2 forcers, particularly methane (high concurrent rapid technological changes, behavioural aspects, and confidence). Such mitigation pathways are characterized by energy- uncertainties about input data present continuous challenges. (high demand reductions, decarbonization of electricity and other fuels, confidence) {2.1.3, 2.3, 2.5.1, 2.6, Technical Annex 2} electrification of energy end use, deep reductions in agricultural emissions, and some form of CDR with carbon storage on land or The Chances of Limiting Warming to 1.5°C sequestration in geological reservoirs. Low energy demand and low and the Requirements for Urgent Action demand for land- and GHG-intensive consumption goods facilitate limiting warming to as close as possible to 1.5°C. {2.2.2, 2.3.1, 2.3.5, Pathways consistent with 1.5°C of warming above pre-industrial 2.5.1, Cross-Chapter Box 9 in Chapter 4}. levels can be identified under a range of assumptions about economic growth, technology developments and lifestyles. In comparison to a 2°C limit, the transformations required to limit However, lack of global cooperation, lack of governance of the required warming to 1.5°C are qualitatively similar but more pronounced energy and land transformation, and increases in resource-intensive and rapid over the next decades (high confidence). 1.5°C implies consumption are key impediments to achieving 1.5°C pathways. very ambitious, internationally cooperative policy environments that