Editing IPCC:AR6/WGIII/Chapter-1 (section)

=== 1.4.8 Policy Impacts ===

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Transformation to different systems will hinge on conscious policy to change the direction in which energy, land use, agriculture and other key sectors develop ( [[#Bataille--2016|Bataille et al. 2016]] ) (Chapters 13 and 16). Policy plays a central role in in land-related systems (Chapter 7), urban development (Chapter 8), improving energy efficiency in buildings (Chapter 9) and transport/mobility (Chapter 10), and decarbonising industrial systems (Chapter 11).

Policy has been and will be central not only because GHG emissions are almost universally under-priced in market economies ( [[#Stern--2017|Stern and Stiglitz 2017]] ; [[#World%20Bank--2019|World Bank 2019]] ), and because of inadequate economic incentives to innovation ( [[#Jaffe--2005|Jaffe et al. 2005]] ), but also due to various delay mechanisms ( [[#Karlsson--2020|Karlsson and Gilek 2020]] ) and multiple sources of path-dependence and lock-in to existing systems ( [[#1.8.2|Section 1.8.2]] ), including: ‘Infrastructure developments and long-lived products that lock societies into GHG-intensive emissions pathways may be difficult or very costly to change, reinforcing the importance of early action for ambitious mitigation ( ''robust evidence'' , ''high agreement'' ).’ (AR5 WGIII p.18).

Many hundreds of policies have been introduced explicitly to mitigate GHG emissions, improve energy efficiency or land use, or to foster low-carbon industries and innovation, with demonstrable impact. The role of policy to date has been most evident in energy efficiency (Sections 5.4 and 5.6) and electricity (Chapter 6). The IPCC Special Report on Renewable Energy already found that: ‘Government policies play a crucial role in accelerating the deployment of RE technologies’ ( [[#IPCC--2011a|IPCC 2011a]] , p. 24). Policy packages since then have driven rapid expansion in renewables capacity and cost reductions (e.g., through the German ''Energiewende'' ), and emission reductions from electricity (most dramatically with the halving of CO 2 emissions from the UK power sector, driven by multiple policy instruments and regulatory changes), as detailed in [[IPCC:Wg3:Chapter:Chapter-6|Chapter 6]] ( [[IPCC:Wg3:Chapter:Chapter-6#6.7.5|Section 6.7.5]] ).

[https://www.ipcc.ch/report/ar6/wg3/chapter/chapter-13 Chapter 13] charts the international evolution of policies and many of the lessons drawn. Attributing the overall impact on emissions is complex, but an emerging literature of several hundred papers indicates impacts on multiple drivers of emissions. Collectively, policies are likely to have curtailed global emissions growth by several GtCO 2 -eq annually already by the mid-2010s (Cross-Chapter Box 10 in Chapter 14). This suggests initial evidence that policy has driven some decoupling (Figure 1.1d) and started to ‘bend the curve’ of global emissions, but more specific attribution to observed trends is not as yet possible. [[#footnote-003|6]]

However, some policies (e.g., subsidies to fossil fuel production or consumption) increase emissions, whilst others (e.g., investment protection) may constrain efforts at mitigation. Also, wider economic and developmental policies have important direct and indirect impacts on emissions. Policy is thus both a driver and a constraint on mitigation.

Synergies and trade-offs arise partly because of the nexus of GHG emissions with other adverse impacts (e.g., local air pollution) and critical resources (e.g., water and food) ( [[#Conway--2015|Conway et al. 2015]] ; [[#Andrews-Speed--2017|Andrews-Speed and Dalin 2017]] ), which also imply interacting policy domains.

The literature shows increasing emphasis on policy packages, including those spanning the different levels of niche/behaviour; existing regimes governing markets and public actors; and strategic and landscape levels ( [[#1.7.3|Section 1.7.3]] ). Chapters 13, 16 and 17 appraise policies for transformation in the context of sustainable development, indicating the importance of policy as a driver at multiple levels and across many actors, with potential for benefits as well as costs at many levels.

National-level legislation may be particularly important to the credibility and long-term stability of policy to reduce the risks, and hence cost, of finance (Chapters 13 and 15), and for encouraging private-sector innovation at scale (Chapter 16), for example, if it offers greater stability and mid-term predictability for carbon prices; [[#Nash--2019|Nash and Steurer (2019)]] find that seven national climate change acts in European countries all act as ‘living policy processes, though to varying extents’.

The importance of policy at multiple levels does not lessen the importance of international policy, for reasons including long-term stability, equity, and scope, but examples of effective implementation policy at international levels remain fewer and governance weaker (Chapter 14).

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