Editing IPCC:AR6/SR15/Chapter-5 (section)

=== 5.5.2 Pathways for Adaptation, Mitigation and Sustainable Development ===

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This section focuses on the growing body of pathways literature describing the dynamic and systemic integration of mitigation and adaptation with sustainable development in the context of a 1.5°C warmer world. These studies are critically important for the identification of ‘enabling’ conditions under which climate and the SDGs can be achieved, and thus help the design of transformation strategies that maximize synergies and avoid potential trade-offs (Sections 5.3 and 5.4). Full integration of sustainable development dimensions is, however, challenging, given their diversity and the need for high temporal, spatial and social resolution to address local effects, including heterogeneity related to poverty and equity (von Stechow et al., 2015) <sup>[[#fn:r272|272]]</sup> . Research on long-term climate change mitigation and adaptation pathways has covered individual SDGs to different degrees. Interactions between climate and other SDGs have been explored for SDGs 2, 3, 4, 6, 7, 8, 12, 14 and 15 (Clarke et al., 2014; Abel et al., 2016; von Stechow et al., 2016; Rao et al., 2017) <sup>[[#fn:r273|273]]</sup> , while interactions with SDGs 1, 5, 11 and 16 remain largely underexplored in integrated long-term scenarios (Zimm et al., 2018) <sup>[[#fn:r274|274]]</sup> .

Quantitative pathways studies now better represent ‘nexus’ approaches to assess sustainable development dimensions. In such approaches (see Chapter 4, Section 4.3.3.8), a subset of sustainable development dimensions are investigated together because of their close relationships (Welsch et al., 2014; Conway et al., 2015; Keairns et al., 2016; Parkinson et al., 2016; Rasul and Sharma, 2016; Howarth and Monasterolo, 2017) <sup>[[#fn:r275|275]]</sup> . Compared to single-objective climate–SDG assessments (Section 5.4.2), nexus solutions attempt to integrate complex interdependencies across diverse sectors in a systems approach for consistent analysis. Recent pathways studies show how water, energy and climate (SDGs 6, 7 and 13) interact (Parkinson et al., 2016; McCollum et al., 2018b) <sup>[[#fn:r276|276]]</sup> and call for integrated water–energy investment decisions to manage systemic risks. For instance, the provision of bioenergy, important in many 1.5°C-consistent pathways, can help resolve ‘nexus challenges’ by alleviating energy security concerns, but can also have adverse ‘nexus impacts’ on food security, water use and biodiversity (Lotze-Campen et al., 2014; Bonsch et al., 2016) <sup>[[#fn:r277|277]]</sup> . Policies that improve resource use efficiency across sectors can maximize synergies for sustainable development (Bartos and Chester, 2014; McCollum et al., 2018b; van Vuuren et al., 2018) <sup>[[#fn:r278|278]]</sup> . Mitigation compatible with 1.5°C can significantly reduce impacts and adaptation needs in the nexus sectors compared to 2°C (Byers et al., 2018) <sup>[[#fn:r279|279]]</sup> . In order to avoid trade-offs due to high carbon pricing of 1.5°C pathways, regulation in specific areas may complement price-based instruments. Such combined policies generally lead also to more early action maximizing synergies and avoiding some of the adverse climate effects for sustainable development (Bertram et al., 2018) <sup>[[#fn:r280|280]]</sup> .

The comprehensive analysis of climate change in the context of sustainable development requires suitable reference scenarios that lend themselves to broader sustainable development analyses. The Shared Socio-Economic Pathways (SSPs) (Chapter 1, Cross-Chapter Box 1 in Chapter 1) (O’Neill et al., 2017a; Riahi et al., 2017) <sup>[[#fn:r281|281]]</sup> constitute an important first step in providing a framework for the integrated assessment of adaptation and mitigation and their climate–development linkages (Ebi et al., 2014) <sup>[[#fn:r282|282]]</sup> . The five underlying SSP narratives (O’Neill et al., 2017a) <sup>[[#fn:r283|283]]</sup> map well into some of the key SDG dimensions, with one of the pathways (SSP1) explicitly depicting sustainability as the main theme (van Vuuren et al., 2017b) <sup>[[#fn:r284|284]]</sup> .

To date, no pathway in the literature proves to achieve all 17 SDGs because several targets are not met or not sufficiently covered in the analysis, hence resulting in a sustainability gap (Zimm et al., 2018) <sup>[[#fn:r285|285]]</sup> . The SSPs facilitate the systematic exploration of different sustainable dimensions under ambitious climate objectives. SSP1 proves to be in line with eight SDGs (3, 7, 8, 9, 10, 11, 13 and 15) and several of their targets in a 2°C warmer world (van Vuuren et al., 2017b; Zimm et al., 2018) <sup>[[#fn:r286|286]]</sup> . However, important targets for SDGs 1, 2 and 4 (i.e., people living in extreme poverty, people living at the risk of hunger and gender gap in years of schooling) are not met in this scenario.

The SSPs show that sustainable socio-economic conditions will play a key role in reaching stringent climate targets (Riahi et al., 2017; Rogelj et al., 2018) <sup>[[#fn:r287|287]]</sup> . Recent modelling work has examined 1.5°C-consistent, stringent mitigation scenarios for 2100 applied to the SSPs, using six different IAMs. Despite the limitations of these models, which are coarse approximations of reality, robust trends can be identified (Rogelj et al., 2018) <sup>[[#fn:r288|288]]</sup> . SSP1 – which depicts broader ‘sustainability’ as well as enhancing equity and poverty reductions – is the only pathway where all models could reach 1.5°C and is associated with the lowest mitigation costs across all SSPs. A decreasing number of models was successful for SSP2, SSP4 and SSP5, respectively, indicating distinctly higher risks of failure due to high growth and energy intensity as well as geographical and social inequalities and uneven regional development. And reaching 1.5°C has even been found infeasible in the less sustainable SSP3 – ‘regional rivalry’ (Fujimori et al., 2017b; Riahi et al., 2017) <sup>[[#fn:r289|289]]</sup> . All these conclusions hold true if a 2°C objective is considered (Calvin et al., 2017; Fujimori et al., 2017b; Popp et al., 2017; Riahi et al., 2017) <sup>[[#fn:r290|290]]</sup> . Rogelj et al. (2018) <sup>[[#fn:r291|291]]</sup> also show that fewer scenarios are, however, feasible across different SSPs in case of 1.5°C, and mitigation costs substantially increase in 1.5°C pathways compared to 2°C pathways.

There is a wide range of SSP-based studies focusing on the connections between adaptation/impacts and different sustainable development dimensions (Hasegawa et al., 2014; Ishida et al., 2014; Arnell et al., 2015; Bowyer et al., 2015; Burke et al., 2015; Lemoine and Kapnick, 2016; Rozenberg and Hallegatte, 2016; Blanco et al., 2017; Hallegatte and Rozenberg, 2017; O’Neill et al., 2017a; Rutledge et al., 2017; Byers et al., 2018) <sup>[[#fn:r292|292]]</sup> . New methods for projecting inequality and poverty (downscaled to sub-national rural and urban levels as well as spatially explicit levels) have enabled advanced SSP-based assessments of locally sustainable development implications of avoided impacts and related adaptation needs. For instance, Byers et al. (2018) <sup>[[#fn:r293|293]]</sup> find that, in a 1.5°C warmer world, a focus on sustainable development can reduce the climate risk exposure of populations vulnerable to poverty by more than an order of magnitude (Section 5.2.2). Moreover, aggressive reductions in between-country inequality may decrease the emissions intensity of global economic growth (Rao and Min, 2018) <sup>[[#fn:r294|294]]</sup> . This is due to the higher potential for decoupling of energy from income growth in lower-income countries, due to high potential for technological advancements that reduce the energy intensity of growth of poor countries – critical also for reaching 1.5°C in a socially and economically equitable way. Participatory downscaling of SSPs in several European Union countries and in Central Asia shows numerous possible pathways of solutions to the 2°C–1.5°C goal, depending on differential visions (Tàbara et al., 2018) <sup>[[#fn:r295|295]]</sup> . Other participatory applications of the SSPs, for example in West Africa (Palazzo et al., 2017) <sup>[[#fn:r296|296]]</sup> and the southeastern United States (Absar and Preston, 2015) <sup>[[#fn:r297|297]]</sup> , illustrate the potentially large differences in adaptive capacity within regions and between sectors.

Harnessing the full potential of the SSP framework to inform sustainable development requires: (i) further elaboration and extension of the current SSPs to cover sustainable development objectives explicitly; (ii) the development of new or variants of current narratives that would facilitate more SDG-focused analyses with climate as one objective (among other SDGs) (Riahi et al., 2017) <sup>[[#fn:r298|298]]</sup> ; (iii) scenarios with high regional resolution (Fujimori et al., 2017b) <sup>[[#fn:r299|299]]</sup> ; (iv) a more explicit representation of institutional and governance change associated with the SSPs (Zimm et al., 2018) <sup>[[#fn:r300|300]]</sup> ; and (v) a scale-up of localized and spatially explicit vulnerability, poverty and inequality estimates, which have emerged in recent publications based on the SSPs (Byers et al., 2018) <sup>[[#fn:r301|301]]</sup> and are essential to investigate equity dimensions (Klinsky and Winkler, 2018) <sup>[[#fn:r302|302]]</sup> .

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