Editing IPCC:AR6/SR15/Chapter-4 (section)

== 4.1 Accelerating the Global Response to Climate Change ==

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This chapter discusses how the global economy and socio-technical and socio-ecological systems can transition to 1.5°C-consistent pathways and adapt to warming of 1.5°C above pre-industrial levels. In the context of systemic transitions, the chapter assesses adaptation and mitigation options, including carbon dioxide removal (CDR), and potential solar radiation modification (SRM) remediative measures (Section 4.3), as well as the enabling conditions that would be required for implementing the rapid and far-reaching global response of limiting warming to 1.5°C (Section 4.4), and render the options more or less feasible (Section 4.5).

The impacts of a 1.5°C-warmer world, while less than in a 2°C-warmer world, would require complementary adaptation and development action, typically at local and national scale. From a mitigation perspective, 1.5°C-consistent pathways require immediate action on a greater and global scale so as to achieve net zero emissions by mid-century, or earlier (Chapter 2). This chapter and Chapter 5 highlight the potential that combined mitigation, development and poverty reduction offer for accelerated decarbonization.

The global context is an increasingly interconnected world, with the human population growing from the current 7.6 billion to over 9 billion by mid-century (UN DESA, 2017) <sup>[[#fn:r1|1]]</sup> . There has been a consistent growth of global economic output, wealth and trade with a significant reduction in extreme poverty. These trends could continue for the next few decades (Burt et al., 2014) <sup>[[#fn:r2|2]]</sup> , potentially supported by new and disruptive information and communication, and nano- and bio-technologies. However, these trends co-exist with rising inequality (Piketty, 2014) <sup>[[#fn:r3|3]]</sup> , exclusion and social stratification, and regions locked in poverty traps (Deaton, 2013) <sup>[[#fn:r4|4]]</sup> that could fuel social and political tensions.

The aftermath of the 2008 financial crisis generated a challenging environment in which leading economists have issued repeated alerts about the ‘discontents of globalisation’ (Stiglitz, 2002) <sup>[[#fn:r5|5]]</sup> , ‘depression economics’ (Krugman, 2009) <sup>[[#fn:r6|6]]</sup> , an excessive reliance of export-led development strategies (Rajan, 2011) <sup>[[#fn:r7|7]]</sup> , and risks of ‘secular stagnation’ due to the ‘saving glut’ that slows down the flow of global savings towards productive 1.5°C-consistent investments (Summers, 2016) <sup>[[#fn:r8|8]]</sup> . Each of these affects the implementation of both 1.5°C-consistent pathways and sustainable development (Chapter 5).

The range of mitigation and adaptation actions that can be deployed in the short run are well-known: for example, low-emission technologies, new infrastructure, and energy efficiency measures in buildings, industry and transport; transformation of fiscal structures; reallocation of investments and human resources towards low-emission assets; sustainable land and water management; ecosystem restoration; enhancement of adaptive capacities to climate risks and impacts; disaster risk management; research and development; and mobilization of new, traditional and indigenous knowledge.

The convergence of short-term development co-benefits from mitigation and adaptation to address ‘everyday development failures’ (e.g., institutions, market structures and political processes) (Hallegatte et al., 2016; Pelling et al., 2018) <sup>[[#fn:r9|9]]</sup> could enhance the adaptive capacity of key systems at risk (e.g ''.'' , water, energy, food, biodiversity, urban, regional and coastal systems) to 1.5°C climate impacts (Chapter 3). The issue is whether aligning 1.5°C-consistent pathways with the Sustainable Development Goals (SDGs) will secure support for accelerated change and a new growth cycle (Stern, 2013, 2015) <sup>[[#fn:r10|10]]</sup> . It is difficult to imagine how a 1.5°C world would be attainde unless the SDG on cities and sustainable urbanization is achieved in developing countries (Revi, 2016) <sup>[[#fn:r11|11]]</sup> , or without reforms in the global financial intermediation system.

Unless affordable and environmentally and socially acceptable CDR becomes feasible and available at scale well before 2050, 1.5°C-consistent pathways will be difficult to realize, especially in overshoot scenarios. The social costs and benefits of 1.5°C-consistent pathways depend on the depth and timing of policy responses and their alignment with short term and long-term development objectives, through policy packages that bring together a diversity of  policy instruments, including public investment (Grubb et al., 2014; Winkler and Dubash, 2015; Campiglio, 2016) <sup>[[#fn:r12|12]]</sup> .

Whatever its potential long-term benefits, a transition to a 1.5°C world may suffer from a lack of broad political and public support, if it exacerbates existing short-term economic and social tensions, including unemployment, poverty, inequality, financial tensions, competitiveness issues and the loss of economic value of carbon-intensive assets (Mercure et al., 2018) <sup>[[#fn:r13|13]]</sup> . The challenge is therefore how to strengthen climate policies without inducing economic collapse or hardship, and to make them contribute to reducing some of the ‘fault lines’ of the world economy (Rajan, 2011) <sup>[[#fn:r14|14]]</sup> .

This chapter reviews literature addressing the alignment of climate with other public policies (e.g., fiscal, trade, industrial, monetary, urban planning, infrastructure, and innovation) and with a greater access to basic needs and services, defined by the SDGs. It also reviews how de-risking low-emission investments and the evolution of the financial intermediation system can help reduce the ‘savings glut’ (Arezki et al., 2016) <sup>[[#fn:r15|15]]</sup> and the gap between cash balances and long-term assets (Aglietta et al., 2015b) <sup>[[#fn:r16|16]]</sup> to support more sustainable and inclusive growth.

As the transitions associated with 1.5°C-consistent pathways require accelerated and coordinated action, in multiple systems across all world regions, they are inherently exposed to risks of freeriding and moral hazards. A key governance challenge is how the convergence of voluntary domestic policies can be organized via aligned global, national and sub-national governance, based on reciprocity (Ostrom and Walker, 2005) <sup>[[#fn:r17|17]]</sup> and partnership (UN, 2016) <sup>[[#fn:r18|18]]</sup> , and how different actors and processes in climate governance can reinforce each other to enable this (Gupta, 2014; Andonova et al., 2017) <sup>[[#fn:r19|19]]</sup> . The emergence of polycentric sources of climate action and transnational and subnational networks that link these efforts (Abbott, 2012) <sup>[[#fn:r20|20]]</sup> offer the opportunity to experiment and learn from different approaches, thereby accelerating approaches led by national governments (Cole, 2015; Jordan et al., 2015) <sup>[[#fn:r21|21]]</sup> .

Section 4.2 of this chapter outlines existing rates of change and attributes of accelerated change. Section 4.3 identifies global systems, and their components, that offer options for this change. Section 4.4 documents the enabling conditions that influence the feasibility of those options, including economic, financial and policy instruments that could trigger the transition to 1.5°C-consistent pathways. Section 4.5 assesses mitigation and adaptation options for feasibility, strategies for implementation and synergies and trade-offs between mitigation and adaptation.

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