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

== 4.3 Systemic Changes for 1.5°C-Consistent Pathways ==

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Section 4.2 emphasizes the importance of systemic change for 1.5°C-consistent pathways. This section translates this into four main system transitions: energy, land and ecosystem, urban and infrastructure, and industrial system transitions. This section assesses the mitigation, adaptation and carbon dioxide removal options that offer the potential for such change within those systems, based on options identified by Chapter 2 and risks and impacts in Chapter 3.

The section puts more emphasis on those adaptation options (Sections 4.3.1–4.3.5) and mitigation options (Sections 4.3.1–4.3.4, 4.3.6 and 4.3.7) that are 1.5°C-relevant and have developed considerably since AR5. They also form the basis for the mitigation and adaptation feasibility assessments in Section 4.5. Section 4.3.8 discusses solar radiation modification methods.

This section emphasizes that no single solution or option can enable a global transition to 1.5°C-consistent pathways or adapting to projected impacts. Rather, accelerating change, much of which is already starting or underway, in multiple global systems, simultaneously and at different scales, could provide the impetus for these system transitions. The feasibility of individual options as well as the potential for synergies and reducing trade-offs will vary according to context and the local enabling conditions. These are explored at a high level in Section 4.5. Policy packages that bring together multiple enabling conditions can provide building blocks for a strategy to scale up implementation and intervention impacts.

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=== 4.3.1 Energy System Transitions ===

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This section discusses the feasibility of mitigation and adaptation options related to the energy system transition. Only options relevant to 1.5°C and with significant changes since AR5 are discussed, which means that for options like hydropower and geothermal energy, the chapter refers to AR5 and does not provide a discussion. Socio-technical inertia of energy options for 1.5°C-consistent pathways are increasingly being surmounted as fossil fuels start to be phased out. Supply-side mitigation and adaptation options and energy demand-side options, including energy efficiency in buildings and transportation, are discussed in Section 4.3.3; options around energy use in industry are discussed in Section 4.3.4.

Section 4.5 assesses the feasibility in a systematic manner based on the approach outlined in Cross-Chapter Box 3 in Chapter 1.

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==== 4.3.1.1 Renewable electricity: solar and wind ====

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All renewable energy options have seen considerable advances over the years since AR5, but solar energy and both onshore and offshore wind energy have had dramatic growth trajectories. They appear well underway to contribute to 1.5°C-consistent pathways (IEA, 2017c; IRENA, 2017b; REN21, 2017) <sup>[[#fn:r86|86]]</sup> .

The largest growth driver for renewable energy since AR5 has been the dramatic reduction in the cost of solar photovoltaics (PV) (REN21, 2017) <sup>[[#fn:r87|87]]</sup> . This has made rooftop solar competitive in sunny areas between 45° north and south latitude (Green and Newman, 2017b) <sup>[[#fn:r88|88]]</sup> , though IRENA (2018) <sup>[[#fn:r89|89]]</sup> suggests it is cost effective in many other places too. Solar PV with batteries has been cost effective in many rural and developing areas (Pueyo and Hanna, 2015; Szabó et al., 2016; Jimenez, 2017) <sup>[[#fn:r90|90]]</sup> , for example 19 million people in Bangladesh now have solar-battery electricity in remote villages and are reporting positive experiences on safety and ease of use (Kabir et al., 2017) <sup>[[#fn:r91|91]]</sup> . Small-scale distributed energy projects are being implemented in developed and developing cities where residential and commercial rooftops offer potential for consumers becoming producers (called prosumers) (ACOLA, 2017; Kotilainen and Saari, 2018) <sup>[[#fn:r92|92]]</sup> . Such prosumers could contribute significantly to electricity generation in sun-rich areas like California (Kurdgelashvili et al., 2016) <sup>[[#fn:r93|93]]</sup> or sub-Saharan Africa in combination with micro-grids and mini-grids (Bertheau et al., 2017) <sup>[[#fn:r94|94]]</sup> . It could also contribute to universal energy access (SDG 7) as shown by (IEA, 2017c) <sup>[[#fn:r95|95]]</sup> .

The feasibility of renewable energy options depends to a large extent on geophysical characteristics of the area where the option is implemented. However, technological advances and policy instruments make renewable energy options increasingly attractive in other areas. For example, solar PV is deployed commercially in areas with low solar insolation, like northwest Europe (Nyholm et al., 2017) <sup>[[#fn:r96|96]]</sup> . Feasibility also depends on grid adaptations (e.g., storage, see below) as renewables grow (IEA, 2017c) <sup>[[#fn:r97|97]]</sup> . For regions with high energy needs, such as industrial areas (see Section 4.3.4), high-voltage DC transmission across long distances would be needed (MacDonald et al., 2016) <sup>[[#fn:r98|98]]</sup> .

Another important factor affecting feasibility is public acceptance, in particular for wind energy and other large-scale renewable facilities (Yenneti and Day, 2016; Rand and Hoen, 2017; Gorayeb et al., 2018) <sup>[[#fn:r99|99]]</sup> that raise landscape management (Nadaï and Labussière, 2017) <sup>[[#fn:r100|100]]</sup> and distributional justice (Yenneti and Day, 2016) <sup>[[#fn:r101|101]]</sup> challenges. Research indicates that financial participation and community engagement can be effective in mitigating resistance (Brunes and Ohlhorst, 2011; Rand and Hoen, 2017) <sup>[[#fn:r102|102]]</sup> (see Section 4.4.3).

Bottom-up studies estimating the use of renewable energy in the future, either at the global or at the national level, are plentiful, especially in the grey literature. It is hotly debated whether a fully renewable energy or electricity system, with or without biomass, is possible (Jacobson et al., 2015, 2017) <sup>[[#fn:r103|103]]</sup> or not (Clack et al., 2017; Heard et al., 2017) <sup>[[#fn:r104|104]]</sup> , and by what year. Scale-up estimates vary with assumptions about costs and technological maturity, as well as local geographical circumstances and the extent of storage used (Ghorbani et al., 2017; REN21, 2017) <sup>[[#fn:r105|105]]</sup> . Several countries have adopted targets of 100% renewable electricity (IEA, 2017c) <sup>[[#fn:r106|106]]</sup> as this meets multiple social, economic and environmental goals and contributes to mitigation of climate change (REN21, 2017) <sup>[[#fn:r107|107]]</sup> .

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==== 4.3.1.2 Bioenergy and biofuels ====

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Bioenergy is renewable energy from biomass. Biofuel is biomass-based energy used in transport. Chapter 2 suggests that pathways limiting warming to 1.5°C would enable supply of 67–310 (median 150) EJ yr <sup>−1</sup> (see Table 2.8) from biomass. Most scenarios find that bioenergy is combined with carbon dioxide capture and storage (CCS, BECCS) if it is available but also find robust deployment of bioenergy independent of the availability of CCS (see Chapter 2, Section 2.3.4.2 and Section 4.3.7 for a discussion of BECCS). Detailed assessments indicate that deployment is similar for pathways limiting global warming to below 2°C (Chum et al., 2011; P. Smith et al., 2014; Creutzig et al., 2015b) <sup>[[#fn:r108|108]]</sup> . There is however ''high agreement'' that the sustainable bioenergy potential in 2050 would be restricted to around 100 EJ yr <sup>−1</sup> (Slade et al., 2014; Creutzig et al., 2015b) <sup>[[#fn:r109|109]]</sup> . Sustainable deployment at such or higher levels envisioned by 1.5°C-consistent pathways may put significant pressure on available land, food production and prices (Popp et al., 2014b; Persson, 2015; Kline et al., 2017; Searchinger et al., 2017) <sup>[[#fn:r110|110]]</sup> , preservation of ecosystems and biodiversity (Creutzig et al., 2015b; Holland et al., 2015; Santangeli et al., 2016) <sup>[[#fn:r111|111]]</sup> , and potential water and nutrient constraints (Gerbens-Leenes et al., 2009; Gheewala et al., 2011; Bows and Smith, 2012; Smith and Torn, 2013; Bonsch et al., 2016; Lampert et al., 2016; Mouratiadou et al., 2016; Smith et al., 2016b; Wei et al., 2016; Mathioudakis et al., 2017) <sup>[[#fn:r112|112]]</sup> ; but there is still ''low agreement'' on these interactions (Robledo-Abad et al., 2017) <sup>[[#fn:r113|113]]</sup> . Some of the disagreement on the sustainable capacity for bioenergy stems from global versus local assessments. Global assessments may mask local dynamics that exacerbate negative impacts and shortages while at the same time niche contexts for deployment may avoid trade-offs and exploit co-benefits more effectively. In some regions of the world (e.g., the case of Brazilian ethanol, see Box 4.7, where land may be less of a constraint, the use of bioenergy is mature and the industry is well developed), land transitions could be balanced with food production and biodiversity to enable a global impact on CO <sub>2</sub> emissions (Jaiswal et al., 2017) <sup>[[#fn:r114|114]]</sup> .

The carbon intensity of bioenergy, key for both bioenergy as an emission-neutral energy option and BECCS as a CDR measure, is still a matter of debate (Buchholz et al., 2016; Liu et al., 2018) <sup>[[#fn:r115|115]]</sup> and depends on management (Pyörälä et al., 2014; Torssonen et al., 2016; Baul et al., 2017; Kilpeläinen et al., 2017) <sup>[[#fn:r116|116]]</sup> ; direct and indirect land-use change emissions (Plevin et al., 2010; Schulze et al., 2012; Harris et al., 2015; Repo et al., 2015; DeCicco et al., 2016; Qin et al., 2016) <sup>[[#fn:r117|117]]</sup> <sup>[[#fn:2|2]]</sup> ; the feedstock considered; and time frame (Zanchi et al., 2012; Daioglou et al., 2017; Booth, 2018; Sterman et al., 2018) <sup>[[#fn:r118|118]]</sup> , as well as the availability of coordinated policies and management to minimize negative side effects and trade-offs, particularly those around food security (Stevanović et al., 2017) <sup>[[#fn:r119|119]]</sup> and livelihood and equity considerations (Creutzig et al., 2013; Calvin et al., 2014) <sup>[[#fn:r120|120]]</sup> .

Biofuels are a part of the transport sector in some cities and countries, and may be deployed as a mitigation option for aviation, shipping and freight transport (see Section 4.3.3.5) as well as industrial decarbonization (IEA, 2017g) <sup>[[#fn:r121|121]]</sup> (Section 4.3.4), though only Brazil has mainstreamed ethanol as a substantial, commercial option. Lower emissions and reduced urban air pollution have been achieved there by use of ethanol and biodiesel as fuels (Hill et al., 2006; Salvo et al., 2017) <sup>[[#fn:r122|122]]</sup> (see Box 4.7).

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==== 4.3.1.3 Nuclear energy ====

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Many scenarios in Chapter 2 and in AR5 (Bruckner et al., 2014) <sup>[[#fn:r123|123]]</sup> project an increase in the use of nuclear power, while others project a decrease. The increase can be realized through existing mature nuclear technologies or new options (generation III/IV reactors, breeder reactors, new uranium and thorium fuel cycles, small reactors or nuclear cogeneration).

Even though scalability and speed of scaling of nuclear plants have historically been high in many nations, such rates are currently not achieved anymore. In the 1960s and 1970s, France implemented a programme to rapidly get 80% of its power from nuclear in about 25 years (IAEA, 2018) <sup>[[#fn:r124|124]]</sup> , but the current time lag between the decision date and the commissioning of plants is observed to be 10-19 years (Lovins et al., 2018) <sup>[[#fn:r125|125]]</sup> . The current deployment pace of nuclear energy is constrained by social acceptability in many countries due to concerns over risks of accidents and radioactive waste management (Bruckner et al., 2014) <sup>[[#fn:r126|126]]</sup> . Though comparative risk assessment shows health risks are low per unit of electricity production (Hirschberg et al., 2016) <sup>[[#fn:r127|127]]</sup> , and land requirement is lower than that of other power sources (Cheng and Hammond, 2017) <sup>[[#fn:r128|128]]</sup> , the political processes triggered by societal concerns depend on the country-specific means of managing the political debates around technological choices and their environmental impacts (Gregory et al., 1993) <sup>[[#fn:r129|129]]</sup> . Such differences in perception explain why the 2011 Fukushima incident resulted in a confirmation or acceleration of phasing out nuclear energy in five countries (Roh, 2017) <sup>[[#fn:r130|130]]</sup> while 30 other countries have continued using nuclear energy, amongst which 13 are building new nuclear capacity, including China, India and the United Kingdom (IAEA, 2017; Yuan et al., 2017) <sup>[[#fn:r131|131]]</sup> .

Costs of nuclear power have increased over time in some developed nations, principally due to market conditions where increased investment risks of high-capital expenditure technologies have become significant. ‘Learning by doing’ processes often failed to compensate for this trend because they were slowed down by the absence of standardization and series effects (Grubler, 2010) <sup>[[#fn:r132|132]]</sup> . What the costs of nuclear power are and have been is debated in the literature (Lovering et al., 2016; Koomey et al., 2017) <sup>[[#fn:r133|133]]</sup> . Countries with liberalized markets that continue to develop nuclear employ de-risking instruments through long-term contracts with guaranteed sale prices (Finon and Roques, 2013) <sup>[[#fn:r134|134]]</sup> . For instance, the United Kingdom works with public guarantees covering part of the upfront investment costs of newly planned nuclear capacity. This dynamic differs in countries such as China and South Korea, where monopolistic conditions in the electric system allow for reducing investment risks, deploying series effects and enhancing the engineering capacities of users due to stable relations between the security authorities and builders (Schneider et al., 2017) <sup>[[#fn:r135|135]]</sup> .

The safety of nuclear plants depends upon the public authorities of each country. However, because accidents affect worldwide public acceptance of this industry, questions have been raised about the risk of economic and political pressures weakening the safety of the plants (Finon, 2013; Budnitz, 2016) <sup>[[#fn:r136|136]]</sup> . This raises the issue of international governance of civil nuclear risks and reinforced international cooperation involving governments, companies and engineering (Walker and Lönnroth, 1983; Thomas, 1988; Finon, 2013) <sup>[[#fn:r137|137]]</sup> , based on the experience of the International Atomic Energy Agency.

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==== 4.3.1.4 Energy storage ====

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The growth in electricity storage for renewables has been around grid flexibility resources (GFR) that would enable several places to source more than half their power from non-hydro renewables (Komarnicki, 2016) <sup>[[#fn:r138|138]]</sup> . Ten types of GFRs within smart grids have been developed (largely since AR5)(Blaabjerg et al., 2004; IRENA, 2013; IEA, 2017d; Majzoobi and Khodaei, 2017) <sup>[[#fn:r139|139]]</sup> , though how variable renewables can be balanced  without hydro or natural gas-based power back-up at a larger scale would still need demonstration. Pumped hydro comprised 150 GW of storage capacity in 2016, and grid-connected battery storage just 1.7 GW, but the latter grew between 2015 to 2016 by 50% (REN21, 2017) <sup>[[#fn:r140|140]]</sup> . Battery storage has been the main growth feature in energy storage since AR5 (Breyer et al., 2017) <sup>[[#fn:r141|141]]</sup> . This appears to the result of significant cost reductions due to mass production for electric vehicles (EVs) (Nykvist and Nilsson, 2015; Dhar et al., 2017) <sup>[[#fn:r142|142]]</sup> . Although costs and technical maturity look increasingly positive, the feasibility of battery storage is challenged by concerns over the availability of resources and the environmental impacts of its production (Peters et al., 2017) <sup>[[#fn:r143|143]]</sup> . Lithium, a common element in the earth’s crust, does not appear to be restricted and large increases in production have happened in recent years with eight new mines in Western Australia where most lithium is produced (GWA, 2016) <sup>[[#fn:r144|144]]</sup> . Emerging battery technologies may provide greater efficiency and recharge rates (Belmonte et al., 2016) <sup>[[#fn:r145|145]]</sup> but remain significantly more expensive due to speed and scale issues compared to lithium ion batteries (Dhar et al., 2017; IRENA, 2017a) <sup>[[#fn:r146|146]]</sup> .

Research and demonstration of energy storage in the form of thermal and chemical systems continues, but large-scale commercial systems are rare (Pardo et al., 2014) <sup>[[#fn:r147|147]]</sup> . Renewably derived synthetic liquid (like methanol and ammonia) and gas (like methane and hydrogen) are increasingly being seen as a feasible storage options for renewable energy (producing fuel for use in industry during times when solar and wind are abundant) (Bruce et al., 2010; Jiang et al., 2010; Ezeji, 2017) <sup>[[#fn:r148|148]]</sup> but, in the case of carbonaceous storage media, would need a renewable source of carbon to make a positive contribution to GHG reduction (von der Assen et al., 2013; Abanades et al., 2017) <sup>[[#fn:r149|149]]</sup> (see also Section 4.3.4.5). The use of electric vehicles as a form of storage has been modelled and evaluated as an opportunity, and demonstrations are emerging (Dhar et al., 2017; Green and Newman, 2017a) <sup>[[#fn:r150|150]]</sup> , but challenges to upscaling remain.

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==== 4.3.1.5 Options for adapting electricity systems to 1.5°C ====

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Climate change has started to disrupt electricity generation and, if climate change adaptation options are not considered, it is predicted that these disruptions will be lengthier and more frequent (Jahandideh-Tehrani et al., 2014; Bartos and Chester, 2015; Kraucunas et al., 2015; van Vliet et al., 2016) <sup>[[#fn:r151|151]]</sup> . Adaptation would both secure vulnerable infrastructure and ensure the necessary generation capacity (Minville et al., 2009; Eisenack and Stecker, 2012; Schaeffer et al., 2012; Cortekar and Groth, 2015; Murrant et al., 2015; Panteli and Mancarella, 2015; Goytia et al., 2016) <sup>[[#fn:r152|152]]</sup> . The literature shows ''high agreement'' that climate change impacts need to be planned for in the design of any kind of infrastructure, especially in the energy sector (Nierop, 2014) <sup>[[#fn:r153|153]]</sup> , including interdependencies with other sectors that require electricity to function, including water, data, telecommunications and transport (Fryer, 2017) <sup>[[#fn:r154|154]]</sup> .

Recent research has developed new frameworks and models that aim to assess and identify vulnerabilities in energy infrastructure and create more proactive responses (Francis and Bekera, 2014; Ouyang and Dueñas-Osorio, 2014; Arab et al., 2015; Bekera and Francis, 2015; Knight et al., 2015; Jeong and An, 2016; Panteli et al., 2016; Perrier, 2016; Erker et al., 2017; Fu et al., 2017) <sup>[[#fn:r155|155]]</sup> . Assessments of energy infrastructure adaptation, while limited, emphasize the need for redundancy (Liu et al., 2017) <sup>[[#fn:r156|156]]</sup> . The implementation of  controllable and islandable microgrids, including the use of residential batteries, can increase resiliency, especially after extreme weather events (Qazi and Young Jr., 2014; Liu et al., 2017) <sup>[[#fn:r157|157]]</sup> . Hybrid renewables-based power systems with non-hydro capacity, such as with high-penetration wind generation, could provide the required system flexibility (Canales et al., 2015) <sup>[[#fn:r158|158]]</sup> . Overall, there is ''high agreement'' that hybrid systems, taking advantage of an array of sources and time of use strategies, can help make electricity generation more resilient (Parkinson and Djilali, 2015) <sup>[[#fn:r159|159]]</sup> , given that energy security standards are in place (Almeida Prado et al., 2016) <sup>[[#fn:r160|160]]</sup> .

Interactions between water and energy are complex (IEA, 2017g) <sup>[[#fn:r161|161]]</sup> . Water scarcity patterns and electricity disruptions will differ across regions. There is ''high agreement'' that mitigation and adaptation options for thermal electricity generation (if that remains fitted with CCS) need to consider increasing water shortages, taking into account other factors such as ambient water resources and demand changes in irrigation water (Hayashi et al., 2018) <sup>[[#fn:r162|162]]</sup> . Increasing the efficiency of power plants can reduce emissions and water needs (Eisenack and Stecker, 2012; van Vliet et al., 2016) <sup>[[#fn:r163|163]]</sup> , but applying CCS would increase water consumption (Koornneef et al., 2012) <sup>[[#fn:r164|164]]</sup> . The technological, economic, social and institutional feasibility of efficiency improvements is high, but insufficient to limit temperature rise to 1.5°C (van Vliet et al., 2016) <sup>[[#fn:r165|165]]</sup> .

In addition, a number of options for water cooling management systems have been proposed, such as hydraulic measures (Eisenack and Stecker, 2012) <sup>[[#fn:r166|166]]</sup> and alternative cooling technologies (Chandel et al., 2011; Eisenack and Stecker, 2012; Bartos and Chester, 2015; Murrant et al., 2015; Bustamante et al., 2016; van Vliet et al., 2016; Huang et al., 2017b) <sup>[[#fn:r167|167]]</sup> . There is ''high agreement'' on the technological and economic feasibility of these technologies, as their absence can severely impact the functioning of the power plant as well as safety and security standards.

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==== 4.3.1.6 Carbon dioxide capture and storage in the power sector ====

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The AR5 (IPCC, 2014b) <sup>[[#fn:r168|168]]</sup> as well as Chapter 2, Section 2.4.2, assign significant emission reductions over the course of this century to CO <sub>2</sub> capture and storage (CCS) in the power sector. This section focuses on CCS in the fossil-fuelled power sector; Section 4.3.4 discusses CCS in non-power industry, and Section 4.3.7 discusses bioenergy with CCS (BECCS). Section 2.4.2 puts the cumulative CO <sub>2</sub> stored from fossil-fuelled power at 410 (199–470 interquartile range) GtCO <sub>2</sub> over this century. Such modelling suggests that CCS in the power sector can contribute to cost-effective achievement of emission reduction requirements for limiting warming to 1.5°C. CCS may also offer employment and political advantages for fossil fuel-dependent economies (Kern et al., 2016) <sup>[[#fn:r169|169]]</sup> , but may entail more limited co-benefits than other mitigation options (that, e.g., generate power) and therefore relies on climate policy incentives for its business case and economic feasibility. Since 2017, two CCS projects in the power sector capture 2.4 MtCO <sub>2</sub> annually, while 30 MtCO <sub>2</sub> is captured annually in all CCS projects (Global CCS Institute, 2017) <sup>[[#fn:r170|170]]</sup> .

The technological maturity of CO <sub>2</sub> capture options in the power sectors has improved considerably (Abanades et al., 2015; Bui et al., 2018) <sup>[[#fn:r171|171]]</sup> , but costs have not come down between 2005 and 2015 due to limited learning in commercial settings and increased energy and resources costs (Rubin et al., 2015) <sup>[[#fn:r172|172]]</sup> . Storage capacity estimates vary greatly, but Section 2.4.2 as well as literature (V. Scott et al., 2015) <sup>[[#fn:r173|173]]</sup> indicate that perhaps 10,000 GtCO <sub>2</sub> could be stored in underground reservoirs. Regional availability of this may not be sufficient, and it requires efforts to have this storage and the corresponding infrastructure available at the necessary rates and times (de Coninck and Benson, 2014) <sup>[[#fn:r174|174]]</sup> . CO <sub>2</sub> retention in the storage reservoir was recently assessed as 98% over 10,000 years for well-managed reservoirs, and 78% for poorly regulated ones (Alcalde et al., 2018) <sup>[[#fn:r175|175]]</sup> .  A paper reviewing 42 studies on public perception of CCS (Seigo et al., 2014) <sup>[[#fn:r176|176]]</sup> found that social acceptance of CCS is predicted by trust, perceived risks and benefits. The technology itself mattered less than the social context of the project. Though insights on communication of CCS projects to the general public and inhabitants of the area around the CO <sub>2</sub> storage sites have been documented over the years, project stakeholders are not consistently implementing these lessons, although some projects have observed good practices (Ashworth et al., 2015) <sup>[[#fn:r177|177]]</sup> .

CCS in the power sector is hardly being realized at scale, mainly because the incremental costs of capture, and the development of transport and storage infrastructures are not sufficiently compensated by market or government incentives (IEA, 2017c) <sup>[[#fn:r178|178]]</sup> . In the two full-scale projects in the power sector mentioned above, part of the capture costs are compensated for by revenues from enhanced oil recovery (EOR) (Global CCS Institute, 2017) <sup>[[#fn:r179|179]]</sup> , demonstrating that EOR helps developing CCS further. EOR is a technique that uses CO <sub>2</sub> to mobilize more oil out of depleting oil fields, leading to additional CO <sub>2</sub> emissions by combusting the additionally recovered oil (Cooney et al., 2015) <sup>[[#fn:r180|180]]</sup> .

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=== 4.3.2 Land and Ecosystem Transitions ===

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This section assesses the feasibility of mitigation and adaptation options related to land use and ecosystems. Land transitions are grouped around agriculture and food, ecosystems and forests, and coastal systems.

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==== 4.3.2.1 Agriculture and food ====

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In a 1.5°C world, local yields are projected to decrease in tropical regions that are major food producing areas of the world (West Africa, Southeast Asia, South Asia, and Central and northern South America) (Schleussner et al., 2016) <sup>[[#fn:r181|181]]</sup> . Some high-latitude regions may benefit from the combined effects of elevated CO <sub>2</sub> and temperature because their average temperatures are below optimal temperature for crops. In both cases there are consequences for food production and quality (Cross-Chapter Box 6 in Chapter 3 on Food Security), conservation agriculture, irrigation, food wastage, bioenergy and the use of novel technologies.

'''Food production and quality''' . Increased temperatures, including 1.5°C warming, would affect the production of cereals such as wheat and rice, impacting food security (Schleussner et al., 2016) <sup>[[#fn:r182|182]]</sup> . There is ''medium agreement'' that elevated CO <sub>2</sub> concentrations can change food composition, with implications for nutritional security (Taub et al., 2008; Högy et al., 2009; DaMatta et al., 2010; Loladze, 2014; De Souza et al., 2015) <sup>[[#fn:r183|183]]</sup> , with the effects being different depending on the region (Medek et al., 2017) <sup>[[#fn:r184|184]]</sup> .

Meta-analyses of the effects of drought, elevated CO <sub>2</sub> , and temperature conclude that at 2°C local warming and above, aggregate production of wheat, maize, and rice are expected to decrease in both temperate and tropical areas (Challinor et al., 2014) <sup>[[#fn:r185|185]]</sup> . These production losses could be lowered if adaptation measures are taken (Challinor et al., 2014) <sup>[[#fn:r186|186]]</sup> , such as developing varieties better adapted to changing climate conditions.

Adaptation options can help ensure access to sufficient, quality food. Such options include conservation agriculture, improved livestock management, increasing irrigation efficiency, agroforestry and management of food loss and waste. Complementary adaptation and mitigation options, for example, the use of climate services (Section 4.3.5), bioenergy (Section 4.3.1) and biotechnology (Section 4.4.4) can also serve to reduce emissions intensity and the carbon footprint of food production.

'''Conservation agriculture (CA)''' is a soil management approach that reduces the disruption of soil structure and biotic processes by minimising tillage. A recent meta-analysis showed that no-till practices work well in water-limited agroecosystems when implemented jointly with residue retention and crop rotation, but when used independently, may decrease yields in other situations (Pittelkow et al., 2014) <sup>[[#fn:r187|187]]</sup> . Additional climate adaptations include adjusting planting times and crop varietal selection and improving irrigation efficiency. Adaptations such as these may increase wheat and maize yields by 7–12% under climate change (Challinor et al., 2014) <sup>[[#fn:r188|188]]</sup> . CA can also help build adaptive capacity ( ''medium evidence, medium agreement'' ) (H. Smith et al., 2017; Pradhan et al., 2018) <sup>[[#fn:r189|189]]</sup> and have mitigation co-benefits through improved fertiliser use or efficient use of machinery and fossil fuels (Harvey et al., 2014; Cui et al., 2018; Pradhan et al., 2018) <sup>[[#fn:r190|190]]</sup> . CA practices can also raise soil carbon and therefore remove CO <sub>2</sub> from the atmosphere (Aguilera et al., 2013; Poeplau and Don, 2015; Vicente-Vicente et al., 2016) <sup>[[#fn:r191|191]]</sup> . However, CA adoption can be constrained by inadequate institutional arrangements and funding mechanisms (Harvey et al., 2014; Baudron et al., 2015; Li et al., 2016; Dougill et al., 2017; H. Smith et al., 2017) <sup>[[#fn:r192|192]]</sup> .

'''Sustainable intensification''' of agriculture consists of agricultural systems with increased production per unit area but with management of the range of potentially adverse impacts on the environment (Pretty and Bharucha, 2014) <sup>[[#fn:r193|193]]</sup> . Sustainable intensification can increase the efficiency of inputs and enhance health and food security (Ramankutty et al., 2018) <sup>[[#fn:r194|194]]</sup> .

'''Livestock management.''' Livestock are responsible for more GHG emissions than all other food sources. Emissions are caused by feed production, enteric fermentation, animal waste, land-use change and livestock transport and processing. Some estimates indicate that livestock supply chains could account for 7.1 GtCO <sub>2</sub> per year, equivalent to 14.5% of global anthropogenic greenhouse gas emissions (Gerber et al., 2013) <sup>[[#fn:r195|195]]</sup> . Cattle (beef, milk) are responsible for about two-thirds of that total, largely due to methane emissions resulting from rumen fermentation (Gerber et al., 2013; Opio et al., 2013) <sup>[[#fn:r196|196]]</sup> .

Despite ongoing gains in livestock productivity and volumes, the increase of animal products in global diets is restricting overall agricultural efficiency gains because of inefficiencies in the conversion of agricultural primary production (e.g., crops) in the feed-animal products pathway (Alexander et al., 2017) <sup>[[#fn:r197|197]]</sup> , offsetting the benefits of improvements in livestock production systems (Clark and Tilman, 2017) <sup>[[#fn:r198|198]]</sup> .

There is increasing agreement that overall emissions from food systems could be reduced by targeting the demand for meat and other livestock products, particularly where consumption is higher than suggested by human health guidelines. Adjusting diets to meet nutritional targets could bring large co-benefits, through GHG mitigation and improvements in the overall efficiency of food systems (Erb et al., 2009; Tukker et al., 2011; Tilman and Clark, 2014; van Dooren et al., 2014; Ranganathan et al., 2016) <sup>[[#fn:r199|199]]</sup> . Dietary shifts could contribute one-fifth of the mitigation needed to hold warming below 2°C, with one-quarter of low-cost options (Griscom et al., 2017) <sup>[[#fn:r200|200]]</sup> . There, however, remains limited evidence of effective policy interventions to achieve such large-scale shifts in dietary choices, and prevailing trends are for increasing rather than decreasing demand for livestock products at the global scale (Alexandratos and Bruinsma, 2012; OECD/FAO, 2017) <sup>[[#fn:r201|201]]</sup> . How the role of dietary shift could change in 1.5°C-consistent pathways is also not clear (see Chapter 2).

Adaptation of livestock systems can include a suite of strategies such as using different breeds and their wild relatives to develop a genetic pool resilient to climatic shocks and longer-term temperature shifts (Thornton and Herrero, 2014) <sup>[[#fn:r202|202]]</sup> , improving fodder and feed management (Bell et al., 2014; Havet et al., 2014) <sup>[[#fn:r203|203]]</sup> and disease prevention and control (Skuce et al., 2013; Nguyen et al., 2016) <sup>[[#fn:r204|204]]</sup> . Most interventions that improve the productivity of livestock systems and enhance adaptation to climate changes would also reduce the emissions intensity of food production, with significant co-benefits for rural livelihoods and the security of food supplies (Gerber et al., 2013; FAO and NZAGRC, 2017a, b, c) <sup>[[#fn:r205|205]]</sup> . Whether such reductions in emission intensity result in lower or higher absolute GHG emissions depends on overall demand for livestock products, indicating the relevance of integrating supply-side with demand-side measures within food security objectives (Gerber et al., 2013; Bajželj et al., 2014) <sup>[[#fn:r206|206]]</sup> . Transitions in livestock production systems (e.g., from extensive to intensive) can also result in significant emission reductions as part of broader land-based mitigation strategies (Havlik et al., 2014) <sup>[[#fn:r207|207]]</sup> .

Overall, there is ''high agreement'' that farm strategies that integrate mixed crop–livestock systems can improve farm productivity and have positive sustainability outcomes (Havet et al., 2014; Thornton and Herrero, 2014; Herrero et al., 2015; Weindl et al., 2015) <sup>[[#fn:r208|208]]</sup> . Shifting towards mixed crop–livestock systems is estimated to reduce agricultural adaptation costs to 0.3% of total production costs while abating deforestation by 76 Mha globally, making it a highly cost-effective adaptation option with mitigation co-benefits (Weindl et al., 2015) <sup>[[#fn:r209|209]]</sup> . Evidence from various regions supports this (Thornton and Herrero, 2015) <sup>[[#fn:r210|210]]</sup> , although the feasible scale varies between regions and systems, as well as being moderated by overall demand in specific food products. In Australia, some farmers have successfully shifted to crop–livestock systems where, each year, they allocate land and forage resources in response to climate and price trends (Bell et al., 2014) <sup>[[#fn:r211|211]]</sup> . However, there can be some unintended negative impacts of such integration, including increased burdens on women, higher requirements of capital, competing uses of crop residues (e.g., feed vs. mulching vs. carbon sequestration) and higher requirements of management skills, which can be a challenge across several low income countries (Thornton and Herrero, 2015; Thornton et al., 2018) <sup>[[#fn:r212|212]]</sup> . Finally, the feasibility of improving livestock efficiency is dependent on socio-cultural context and acceptability: there remain significant issues around widespread adoption of crossbred animals, especially by smallholders (Thornton et al., 2018) <sup>[[#fn:r213|213]]</sup> .

'''Irrigation efficiency.''' Irrigation efficiency is especially critical since water endowments are expected to change, with  20–60 Mha of global cropland being projected to revert from irrigated to rain-fed land, while other areas will receive higher precipitation in shorter time spans, thus affecting irrigation demand (Elliott et al., 2014) <sup>[[#fn:r214|214]]</sup> . While increasing irrigation system efficiency is necessary, there is mixed evidence on how to enact efficiency improvements (Fader et al., 2016; Herwehe and Scott, 2018) <sup>[[#fn:r215|215]]</sup> . Physical and technical strategies include building large-scale reservoirs or dams, renovating or deepening irrigation channels, building on-farm rainwater harvesting structures, lining ponds, channels and tanks to reduce losses through percolation and evaporation, and investing in small infrastructure such as sprinkler or drip irrigation sets (Varela-Ortega et al., 2016; Sikka et al., 2018) <sup>[[#fn:r216|216]]</sup> . Each strategy has differing costs and benefits relating to unique biophysical, social, and economic contexts. Also, increasing irrigation efficiency may foster higher dependency on irrigation, resulting in a heightened sensitivity to climate that may be maladaptive in the long term (Lindoso et al., 2014) <sup>[[#fn:r217|217]]</sup> .

Improvements in irrigation efficiency would need to be supplemented with ancillary activities, such as shifting to crops that require less water and improving soil and moisture conservation (Fader et al., 2016; Hong and Yabe, 2017; Sikka et al., 2018) <sup>[[#fn:r218|218]]</sup> . Currently, the feasibility of improving irrigation efficiency is constrained by issues of replicability across scale and sustainability over time (Burney and Naylor, 2012) <sup>[[#fn:r219|219]]</sup> , institutional barriers and inadequate market linkages (Pittock et al., 2017) <sup>[[#fn:r220|220]]</sup> .

Growing evidence suggests that investing in behavioural shifts towards using irrigation technology such as micro-sprinklers or drip irrigation, is an effective and quick adaptation strategy (Varela-Ortega et al., 2016; Herwehe and Scott, 2018; Sikka et al., 2018) <sup>[[#fn:r221|221]]</sup> as opposed to large dams which have high financial, ecological and social costs (Varela-Ortega et al., 2016) <sup>[[#fn:r222|222]]</sup> . While improving irrigation efficiency is technically feasible (R. Fishman et al., 2015) <sup>[[#fn:r223|223]]</sup> and has clear benefits for environmental values (Pfeiffer and Lin, 2014; R. Fishman et al., 2015) <sup>[[#fn:r224|224]]</sup> , feasibility is regionally differentiated as shown by examples as diverse as Kansas (Jägermeyr et al., 2015) <sup>[[#fn:r225|225]]</sup> , India (R. Fishman et al., 2015) <sup>[[#fn:r226|226]]</sup> and Africa (Pittock et al., 2017) <sup>[[#fn:r227|227]]</sup> .

'''Agroforestry.''' The integration of trees and shrubs into crop and livestock systems, when properly managed, can potentially restrict soil erosion, facilitate water infiltration, improve soil physical properties and buffer against extreme events (Lasco et al., 2014; Mbow et al., 2014; Quandt et al., 2017; Sida et al., 2018) <sup>[[#fn:r228|228]]</sup> . There is ''medium evidence'' and ''high agreement'' on the feasibility of agroforestry practices that enhance productivity, livelihoods and carbon storage (Lusiana et al., 2012; Murthy, 2013; Coulibaly et al., 2017; Sida et al., 2018) <sup>[[#fn:r229|229]]</sup> , including from indigenous production systems (Coq-Huelva et al., 2017) <sup>[[#fn:r230|230]]</sup> , with variation by region, agroforestry type, and climatic conditions (Place et al., 2012; Coe et al., 2014; Mbow et al., 2014; Iiyama et al., 2017; Abdulai et al., 2018) <sup>[[#fn:r231|231]]</sup> . Long-term studies examining the success of agroforestry, however, are rare (Coe et al., 2014; Meijer et al., 2015; Brockington et al., 2016; Zomer et al., 2016) <sup>[[#fn:r232|232]]</sup> .

The extent to which agroforestry practices employed at the farm level could be scaled up globally while satisfying growing food demand is relatively unknown. Agroforestry adoption has been relatively low and uneven (Jacobi et al., 2017; Hernández-Morcillo et al., 2018) <sup>[[#fn:r233|233]]</sup> , with constraints including the expense of establishment and lack of reliable financial support, insecure land tenure, landowner’s lack of experience with trees, complexity of management practices, fluctuating market demand and prices for different food and fibre products, the time and knowledge required for management, low intermediate benefits to offset revenue lags, and inadequate market access (Pattanayak et al., 2003; Mercer, 2004; Sendzimir et al., 2011; Valdivia et al., 2012; Coe et al., 2014; Meijer et al., 2015; Coulibaly et al., 2017; Jacobi et al., 2017) <sup>[[#fn:r234|234]]</sup> .

'''Managing food loss and waste''' . The way food is produced, processed and transported strongly influences GHG emissions. Around one-third of the food produced on the planet is not consumed (FAO, 2013) <sup>[[#fn:r235|235]]</sup> , affecting food security and livelihoods (See Cross-Chapter Box 6 on Food Security in Chapter 3). Food wastage is a combination of food loss – the decrease in mass and nutritional value of food due to poor infrastructure, logistics, and lack of storage technologies and management – and food waste that derives from inappropriate human consumption that leads to food spoilage associated with inferior quality or overproduction. Food wastage could lead to an increase in emissions estimated to 1.9–2.5 GtCO <sub>2</sub> -eq yr <sup>−1</sup> (Hiç et al., 2016) <sup>[[#fn:r236|236]]</sup> .

Decreasing food wastage has high mitigation and adaptation potential and could play an important role in land transitions towards 1.5°C, provided that reduced food waste results in lower production-side emissions rather than increased consumption (Foley et al., 2011) <sup>[[#fn:r237|237]]</sup> . There is ''medium agreement'' that a combination of individual–institutional behaviour (Refsgaard and Magnussen, 2009; Thornton and Herrero, 2014) <sup>[[#fn:r238|238]]</sup> , and improved technologies and management (Lin et al., 2013; Papargyropoulou et al., 2014) <sup>[[#fn:r239|239]]</sup> can transform food waste into products with marketable value. Institutional behaviour depends on investment and policies, which if adequately addressed could enable mitigation and adaptation co-benefits in a relatively short time.

'''Novel technologies.''' New molecular biology tools have been developed that can lead to fast and precise genome modification (De Souza et al., 2016; Scheben et al., 2016) <sup>[[#fn:r240|240]]</sup> (e.g., CRISPR Cas9; Ran et al., 2013; Schaeffer and Nakata, 2015) <sup>[[#fn:r241|241]]</sup> . Such genome editing tools may moderately assist in mitigation and adaptation of agriculture in relation to climate changes, elevated CO <sub>2</sub> , drought and flooding (DaMatta et al., 2010; De Souza et al., 2015, 2016) <sup>[[#fn:r242|242]]</sup> . These tools could contribute to developing new plant varieties that can adapt to warming of 1.5°C and overshoot, potentially avoiding some of the costs of crop shifting (Schlenker and Roberts, 2009; De Souza et al., 2016) <sup>[[#fn:r243|243]]</sup> . However, biosafety concerns and government regulatory systems can be a major barrier to the use of these tools as this increases the time and cost of turning scientific discoveries into ready applicable technologies (Andow and Zwahlen, 2006; Maghari and Ardekani, 2011) <sup>[[#fn:r244|244]]</sup> .

The strategy of reducing enteric methane emissions by ruminants through the development of inhibitors or vaccines has already been attempted with some successes, although the potential for application at scale and in different situations remains uncertain. A methane inhibitor has been demonstrated to reduce methane from feedlot systems by 30% over a 12-week period (Hristov et al., 2015) <sup>[[#fn:r245|245]]</sup> with some productivity benefits, but the ability to apply it in grazing systems will depend on further technological developments as well as costs and incentives. A vaccine could potentially modify the microbiota of the rumen and be applicable even in extensive grazing systems by reducing the presence of methanogenic micro-organisms (Wedlock et al., 2013) <sup>[[#fn:r246|246]]</sup> but has not yet been successfully demonstrated to reduce emissions in live animals. Selective breeding for lower-emitting ruminants is becoming rapidly feasible, offering small but cumulative emissions reductions without requiring substantial changes in farm systems (Pickering et al., 2015) <sup>[[#fn:r247|247]]</sup> .

Technological innovation in culturing marine and freshwater micro and macro flora has significant potential to expand food, fuel and fibre resources, and could reduce impacts on land and conventional agriculture (Greene et al., 2017) <sup>[[#fn:r248|248]]</sup> .

Technological innovation could assist in increased agricultural efficiency (e.g., via precision agriculture), decrease food wastage and genetics that enhance plant adaptation traits (Section 4.4.4). Technological and associated management improvements may be ways to increase the efficiency of contemporary agriculture to help produce enough food to cope with population increases in a 1.5°C warmer world, and help reduce the pressure on natural ecosystems and biodiversity.

<div id="section-4-3-2-2"></div>

<span id="forests-and-other-ecosystems"></span>
==== 4.3.2.2 Forests and other ecosystems ====

<div id="section-4-3-2-2-block-1"></div>

'''Ecosystem restoration.''' Biomass stocks in tropical, subtropical, temperate and boreal biomes currently hold 1085, 194, 176, 190 Gt CO <sub>2</sub> , respectively. Conservation and restoration can enhance these natural carbon sinks (Erb et al., 2017) <sup>[[#fn:r249|249]]</sup> .

Recent studies explore options for conservation, restoration and improved land management estimating up to 23 GtCO <sub>2</sub> (Griscom et al., 2017) <sup>[[#fn:r250|250]]</sup> . Mitigation potentials are dominated by reduced rates of deforestation, reforestation and forest management, and concentrated in tropical regions (Houghton, 2013; Canadell and Schulze, 2014; Grace et al., 2014; Houghton et al., 2015; Griscom et al., 2017) <sup>[[#fn:r251|251]]</sup> . Much of the literature focuses on REDD+ (reducing emissions from deforestation and forest degradation) as an institutional mechanism. However, restoration and management activities need not be limited to REDD+, and locally adapted implementation may keep costs low, capitalize on co-benefits and ensure consideration of competing for socio-economic goals (Jantke et al., 2016; Ellison et al., 2017; Perugini et al., 2017; Spencer et al., 2017) <sup>[[#fn:r252|252]]</sup> .

Half of the estimated potential can be achieved at &lt;100 USD/tCO <sub>2</sub> ; and a third of the cost-effective potential at &lt;10 USD/tCO <sub>2</sub> (Griscom et al., 2017) <sup>[[#fn:r253|253]]</sup> . Variation of costs in projects aiming to reduce emissions from deforestation is high when considering opportunity and transaction costs (Dang Phan et al., 2014; Overmars et al., 2014; Ickowitz et al., 2017; Rakatama et al., 2017) <sup>[[#fn:r254|254]]</sup> .

However, the focus on forests raises concerns of cross-biome leakage ( ''medium evidence, low agreement'' ) (Popp et al., 2014a; Strassburg et al., 2014; Jayachandran et al., 2017) <sup>[[#fn:r255|255]]</sup> and encroachment on other ecosystems (Veldman et al., 2015) <sup>[[#fn:r256|256]]</sup> . Reducing rates of deforestation constrains the land available for agriculture and grazing, with trade-offs between diets, higher yields and food prices (Erb et al., 2016a; Kreidenweis et al., 2016) <sup>[[#fn:r257|257]]</sup> . Forest restoration and conservation are compatible with biodiversity (Rey Benayas et al., 2009; Jantke et al., 2016) <sup>[[#fn:r258|258]]</sup> and available water resources; in the tropics, reducing rates of deforestation maintains cooler surface temperatures (Perugini et al., 2017) <sup>[[#fn:r259|259]]</sup> and rainfall (Ellison et al., 2017) <sup>[[#fn:r260|260]]</sup> .

Its multiple potential co-benefits have made REDD+ important for local communities, biodiversity and sustainable landscapes (Ngendakumana et al., 2017; Turnhout et al., 2017) <sup>[[#fn:r261|261]]</sup> . There is ''low agreement'' on whether climate impacts will reverse mitigation benefits of restoration (Le Page et al., 2013) <sup>[[#fn:r262|262]]</sup> by increasing the likelihood of disturbance (Anderegg et al., 2015) <sup>[[#fn:r263|263]]</sup> , or reinforce them through carbon fertilization (P. Smith et al., 2014) <sup>[[#fn:r264|264]]</sup> .

Emerging regional assessments offer new perspectives for upscaling. Strengthening coordination, additional funding sources, and access and disbursement points increase the potential of REDD+ in working towards 2°C and 1.5°C limits (Well and Carrapatoso, 2017) <sup>[[#fn:r265|265]]</sup> . While there are indications that land tenure has a positive impact (Sunderlin et al., 2014) <sup>[[#fn:r266|266]]</sup> , a meta-analysis by Wehkamp et al. (2018a) <sup>[[#fn:r267|267]]</sup> shows that there is ''medium evidence'' and ''low agreement'' on which aspects of governance improvements are supportive of conservation. Local benefits, especially for indigenous communities, will only be accrued if land tenure is respected and legally protected, which is not often the case (Sunderlin et al., 2014; Brugnach et al., 2017) <sup>[[#fn:r268|268]]</sup> . Although payments for reduced rates of deforestation may benefit the poor, the most vulnerable populations could have limited, uneven access (Atela et al., 2014) <sup>[[#fn:r269|269]]</sup> and face lower opportunity costs from deforestation (Ickowitz et al., 2017) <sup>[[#fn:r270|270]]</sup> .

'''Community-based adaptation (CbA).''' There is ''medium evidence'' and ''high agreement'' for the use of CbA. The specific actions to take will depend upon the location, context, and vulnerability of the specific community. CbA is defined as ‘a community-led process, based on communities’ priorities, needs, knowledge, and capacities, which aim to empower people to plan for and cope with the impacts of climate change’ (Reid et al., 2009) <sup>[[#fn:r271|271]]</sup> . The integration of CbA with ecosystems-based adaptation (EbA) has been increasingly promoted, especially in efforts to alleviate poverty (Mannke, 2011; Reid, 2016) <sup>[[#fn:r272|272]]</sup> .

Despite the potential and advantages of both CbA and EbA, including knowledge exchange, information access and increased social capital and equity; institutional and governance barriers still constitute a challenge for local adaptation efforts (Wright et al., 2014; Fernández-Giménez et al., 2015) <sup>[[#fn:r273|273]]</sup> .

'''Wetland management.''' In wetland ecosystems, temperature rise has direct and irreversible impacts on species functioning and distribution, ecosystem equilibrium and services, and second-order impacts on local livelihoods (see Chapter 3, Section 3.4.3). The structure and function of wetland systems are changing due to climate change. Wetland management strategies, including adjustments in infrastructural, behavioural, and institutional practices have clear implications for adaptation (Colloff et al., 2016b; Finlayson et al., 2017; Wigand et al., 2017) <sup>[[#fn:r274|274]]</sup>

Despite international initiatives on wetland restoration and management through the Ramsar Convention on Wetlands, policies have not been effective (Finlayson, 2012; Finlayson et al., 2017) <sup>[[#fn:r275|275]]</sup> . Institutional reform, such as flexible, locally relevant governance, drawing on principles of adaptive co-management, and multi-stakeholder participation becomes increasingly necessary for effective wetland management (Capon et al., 2013; Finlayson et al., 2017) <sup>[[#fn:r276|276]]</sup> .

<div id="section-4-3-2-3"></div>

<span id="coastal-systems"></span>
==== 4.3.2.3 Coastal systems ====

<div id="section-4-3-2-3-block-1"></div>

'''Managing coastal stress.''' Particularly to allow for the landward relocation of coastal ecosystems under a transition to a 1.5°C warmer world, planning for climate change would need to be integrated with the use of coastlines by humans (Saunders et al., 2014; Kelleway et al., 2017) <sup>[[#fn:r277|277]]</sup> . Adaptation options for managing coastal stress include coastal hardening through the building of seawalls and the re-establishment of coastal ecosystems such as mangroves (André et al., 2016; Cooper et al., 2016) <sup>[[#fn:r278|278]]</sup> . While the feasibility of the solutions is high, they are expensive to scale ( ''robust evidence, medium agreement'' ).

There is ''low evidence'' and ''high agreement'' that reducing the impact of local stresses (Halpern et al., 2015) <sup>[[#fn:r279|279]]</sup> will improve the resilience of marine ecosystems as they transition to a 1.5°C world (O’Leary et al., 2017) <sup>[[#fn:r280|280]]</sup> .  Approaches to reducing local stresses are considered feasible, cost-effective and highly scalable. Ecosystem resilience may be increased through alternative livelihoods (e.g., sustainable aquaculture), which are among a suite of options for building resilience in coastal ecosystems. These options enjoy high levels of feasibility yet are expensive, which stands in the way of scalability ( ''robust evidence, medium agreement'' ) (Hiwasaki et al., 2015; Brugnach et al., 2017) <sup>[[#fn:r281|281]]</sup> .

Working with coastal communities has the potential for improving the resilience of coastal ecosystems. Combined with the advantages of using indigenous knowledge to guide transitions, solutions can be more effective when undertaken in partnership with local communities, cultures, and knowledge (See Box 4.3).

'''Restoration of coastal ecosystems and fisheries.''' Marine restoration is expensive compared to terrestrial restoration, and the survival of projects is currently low, with success depending on the ecosystem and site, rather than the size of the financial investment (Bayraktarov et al., 2016) <sup>[[#fn:r282|282]]</sup> . Mangrove replanting shows evidence of success globally, with numerous examples of projects that have established forests (Kimball et al., 2015; Bayraktarov et al., 2016) <sup>[[#fn:r283|283]]</sup> .

Efforts with reef-building corals have been attempted with a low level of success (Bayraktarov et al., 2016) <sup>[[#fn:r284|284]]</sup> . Technologies to help re-establish coral communities are limited (Rinkevich, 2014) <sup>[[#fn:r285|285]]</sup> , as are largely untested disruptive technologies (e.g., genetic manipulation, assisted evolution) (van Oppen et al., 2015) <sup>[[#fn:r286|286]]</sup> . Current technologies also have trouble scaling given the substantial costs and investment required (Bayraktarov et al., 2016) <sup>[[#fn:r287|287]]</sup> .

Johannessen and Macdonald (2016) <sup>[[#fn:r288|288]]</sup> report the ‘blue carbon’ sink to be 0.4–0.8% of global anthropogenic emissions. However, this does not adequately account for post-depositional processes and could overestimate removal potentials, subject to a risk of reversal. Seagrass beds will thus not contribute significantly to enabling 1.5°C-consistent pathways.

<span id="urban-and-infrastructure-system-transitions"></span>
=== 4.3.3 Urban and Infrastructure System Transitions ===

<div id="section-4-3-3-block-1"></div>

There will be approximately 70 million additional urban residents every year through to the middle part of this century (UN DESA, 2014) <sup>[[#fn:r289|289]]</sup> . The majority of these new urban citizens will reside in small and medium-sized cities in low- and middle-income countries (Cross-Chapter Box 13 in Chapter 5). The combination of urbanization and economic and infrastructure development could account for an additional 226 GtCO <sub>2</sub> by 2050 (Bai et al. 2018). However, urban systems can harness the mega-trends of urbanization, digitalization, financialization and growing sub-national commitment to smart cities, green cities, resilient cities, sustainable cities and adaptive cities, for the type of transformative change required by 1.5°C-consistent pathways (SDSN, 2013; Parag and Sovacool, 2016; Roberts, 2016; Wachsmuth et al., 2016; Revi, 2017; Solecki et al., 2018) <sup>[[#fn:r290|290]]</sup> . There is a growing number of urban climate responses driven by cost-effectiveness, development, work creation and inclusivity considerations (Solecki et al., 2013; Ahern et al., 2014; Floater et al., 2014; Revi et al., 2014a; Villarroel Walker et al., 2014; Kennedy et al., 2015; Rodríguez, 2015; McGranahan et al., 2016; Dodman et al., 2017a; Newman et al., 2017; UN-Habitat, 2017; Westphal et al., 2017) <sup>[[#fn:r291|291]]</sup> .

In addition, low-carbon cities could reduce the need to deploy carbon dioxide removal (CDR) and solar radiation modification (SRM) (Fink, 2013; Thomson and Newman, 2016) <sup>[[#fn:r292|292]]</sup> .

Cities are also places in which the risks associated with warming of 1.5°C, such as heat stress, terrestrial and coastal flooding, new disease vectors, air pollution and water scarcity, will coalesce (see Chapter 3, Section 3.3) (Dodman et al., 2017a; Satterthwaite and Bartlett, 2017) <sup>[[#fn:r293|293]]</sup> . Unless adaptation and mitigation efforts are designed around the need to decarbonize urban societies in the developed world and provide low-carbon solutions to the needs of growing urban populations in developing countries, they will struggle to deliver the pace or scale of change required by 1.5°C-consistent pathways (Hallegatte et al., 2013; Villarroel Walker et al., 2014; Roberts, 2016; Solecki et al., 2018) <sup>[[#fn:r294|294]]</sup> . The pace and scale of urban climate responses can be enhanced by attention to social equity (including gender equity), urban ecology (Brown and McGranahan, 2016; Wachsmuth et al., 2016; Ziervogel et al., 2016a) <sup>[[#fn:r295|295]]</sup> and participation in sub-national networks for climate action (Cole, 2015; Jordan et al., 2015) <sup>[[#fn:r296|296]]</sup> .

The long-lived urban transport, water and energy systems that will be constructed in the next three decades to support urban populations in developing countries and to retrofit cities in developed countries will have to be different to those built in Europe and North America in the 20th century, if they are to support the required transitions (Freire et al., 2014; Cartwright, 2015; McPhearson et al., 2016; Roberts, 2016; Lwasa, 2017) <sup>[[#fn:r297|297]]</sup> . Recent literature identifies energy, infrastructure, appliances, urban planning, transport and adaptation options as capable of facilitating systemic change. It is these aspects of the urban system that are discussed below and from which options in Section 4.5 are selected.

<div id="section-4-3-3-1"></div>

<span id="urban-energy-systems"></span>
==== 4.3.3.1 Urban energy systems ====

<div id="section-4-3-3-1-block-1"></div>

Urban economies tend to be more energy intensive than national economies due to higher levels of per capita income, mobility and consumption (Kennedy et al., 2015; Broto, 2017; Gota et al., 2018) <sup>[[#fn:r298|298]]</sup> . However, some urban systems have begun decoupling development from the consumption of fossil fuel-powered energy through energy efficiency, renewable energy and locally managed smart grids (Dodman, 2009; Freire et al., 2014; Eyre et al., 2018; Glazebrook and Newman, 2018) <sup>[[#fn:r299|299]]</sup> .

The rapidly expanding cities of Africa and Asia, where energy poverty currently undermines adaptive capacity (Westphal et al., 2017; Satterthwaite et al., 2018) <sup>[[#fn:r300|300]]</sup> , have the opportunity to benefit from recent price changes in renewable energy technologies to enable clean energy access to citizens (SDG 7) (Cartwright, 2015; Watkins, 2015; Lwasa, 2017; Kennedy et al., 2018; Teferi and Newman, 2018) <sup>[[#fn:r301|301]]</sup> . This will require strengthened energy governance in these countries (Eberhard et al., 2017) <sup>[[#fn:r302|302]]</sup> . Where renewable energy displaces paraffin, wood fuel or charcoal feedstocks in informal urban settlements, it provides the co-benefits of improved indoor air quality, reduced fire risk and reduced deforestation, all of which can enhance adaptive capacity and strengthen demand for this energy (Newham and Conradie, 2013; Winkler, 2017; Kennedy et al., 2018; Teferi and Newman, 2018) <sup>[[#fn:r303|303]]</sup> .

<div id="section-4-3-3-2"></div>

<span id="urban-infrastructure-buildings-and-appliances"></span>
==== 4.3.3.2 Urban infrastructure, buildings and appliances ====

<div id="section-4-3-3-2-block-1"></div>

Buildings are responsible for 32% of global energy consumption (IEA, 2016c) <sup>[[#fn:r304|304]]</sup> and have a large energy saving potential with available and demonstrated technologies such as energy efficiency improvements in technical installations and in thermal insulation (Toleikyte et al., 2018) <sup>[[#fn:r305|305]]</sup> and energy sufficiency (Thomas et al., 2017) <sup>[[#fn:r306|306]]</sup> . Kuramochi et al. (2018) <sup>[[#fn:r307|307]]</sup> show that 1.5°C-consistent pathways require building emissions to be reduced by 80–90% by 2050, new construction to be fossil-free and near-zero energy by 2020, and an increased rate of energy refurbishment of existing buildings to 5% per annum in OECD (Organisation for Economic Co-operation and Development) countries (see also Section 4.2.1).

Based on the IEA-ETP (IEA, 2017g) <sup>[[#fn:r308|308]]</sup> , Chapter 2 identifies large saving potential in heating and cooling through improved building design, efficient equipment, lighting and appliances. Several examples of net zero energy in buildings are now available (Wells et al., 2018) <sup>[[#fn:r309|309]]</sup> . In existing buildings, refurbishment enables energy saving (Semprini et al., 2017; Brambilla et al., 2018; D’Agostino and Parker, 2018; Sun et al., 2018) <sup>[[#fn:r310|310]]</sup> and cost savings (Toleikyte et al., 2018; Zangheri et al., 2018) <sup>[[#fn:r311|311]]</sup> .

Reducing the energy embodied in building materials provides further energy and GHG savings (Cabeza et al., 2013; Oliver and Morecroft, 2014; Koezjakov et al., 2018) <sup>[[#fn:r312|312]]</sup> , in particular through increased use of bio-based materials (Lupíšek et al., 2015) <sup>[[#fn:r313|313]]</sup> and wood construction (Ramage et al., 2017) <sup>[[#fn:r314|314]]</sup> . The United Nations Environment Programme (UNEP3) <sup>[[#fn:3|3]]</sup> estimates that improving embodied energy, thermal performance, and direct energy use of buildings can reduce emissions by 1.9 GtCO <sub>2</sub> e yr <sup>−1</sup> (UNEP, 2017b) <sup>[[#fn:r315|315]]</sup> '','' with an additional reduction of 3 GtCO <sub>2</sub> e yr <sup>−1</sup> through energy efficient appliances and lighting (UNEP, 2017b) <sup>[[#fn:r316|316]]</sup> ''.'' Further increasing the energy efficiency of appliances and lighting, heating and cooling offers the potential for further savings (Parikh and Parikh, 2016; Garg et al., 2017) <sup>[[#fn:r317|317]]</sup> .

Smart technology, drawing on the internet of things (IoT) and building information modelling, offers opportunities to accelerate energy efficiency in buildings and cities (Moreno-Cruz and Keith, 2013; Hoy, 2016) <sup>[[#fn:r318|318]]</sup> (see also Section 4.4.4). Some cities in developing countries are drawing on these technologies to adopt ‘leapfrog’ infrastructure, buildings and appliances to pursue low-carbon development (Newman et al., 2017; Teferi and Newman, 2017) <sup>[[#fn:r319|319]]</sup> (Cross-Chapter Box 13 in Chapter 5).

<div id="section-4-3-3-3"></div>

<span id="urban-transport-and-urban-planning"></span>
==== 4.3.3.3 Urban transport and urban planning ====

<div id="section-4-3-3-3-block-1"></div>

Urban form impacts demand for energy (Sims et al., 2014) <sup>[[#fn:r320|320]]</sup> and other welfare related factors: a meta-analysis of 300 papers reported energy savings of 26 USD per person per year attributable to a 10% increase in urban population density (Ahlfeldt and Pietrostefani, 2017) <sup>[[#fn:r321|321]]</sup> . Significant reductions in car use are associated with dense, pedestrianized cities and towns and medium-density transit corridors (Newman and Kenworthy, 2015; Newman et al., 2017) <sup>[[#fn:r322|322]]</sup> relative to low-density cities in which car dependency is high (Schiller and Kenworthy, 2018) <sup>[[#fn:r323|323]]</sup> . Combined dense urban forms and new mass transit systems in Shanghai and Beijing have yielded less car use (Gao and Newman, 2018) <sup>[[#fn:r324|324]]</sup> (see Box 4.9). Compact cities also create the passenger density required to make public transport more financially viable (Rode et al., 2014; Ahlfeldt and Pietrostefani, 2017) <sup>[[#fn:r325|325]]</sup> and enable combinations of cleaner fuel feedstocks and urban smart grids, in which vehicles form part of the storage capacity (Oldenbroek et al., 2017) <sup>[[#fn:r326|326]]</sup> . Similarly, the spatial organization of urban energy influenced the trajectories of urban development in cities as diverse as Hong Kong, Bengaluru and Maputo (Broto, 2017) <sup>[[#fn:r327|327]]</sup> .

The informal settlements of middle- and low-income cities, where urban density is more typically associated with a range of water- and vector-borne health risks, may provide a notable exception to the adaptive advantages of urban density (Mitlin and Satterthwaite, 2013; Lilford et al., 2017) <sup>[[#fn:r328|328]]</sup> unless new approaches and technologies are harnessed to accelerate slum upgrading (Teferi and Newman, 2017) <sup>[[#fn:r329|329]]</sup> .

Scenarios consistent with 1.5°C depend on a roughly 15% reduction in final energy use by the transport sector by 2050 relative to 2015 (Chapter 2, Figure 2.12). In one analysis the phasing out of fossil fuel passenger vehicle sales by 2035–2050 was identified as a benchmark for aligning with 1.5°C-consistent pathways (Kuramochi et al., 2018) <sup>[[#fn:r330|330]]</sup> . Reducing emissions from transport has lagged the power sector (Sims et al., 2014; Creutzig et al., 2015a) <sup>[[#fn:r331|331]]</sup> , but evidence since AR5 suggests that cities are urbanizing and re-urbanizing in ways that coordinate transport sector adaptation and mitigation (Colenbrander et al., 2017; Newman et al., 2017; Salvo et al., 2017; Gota et al., 2018) <sup>[[#fn:r332|332]]</sup> . The global transport sector could reduce 4.7 GtCO2e yr <sup>−1</sup> (4.1–5.3) by 2030. This is significantly more than is predicted by integrated assessment models (UNEP, 2017b) <sup>[[#fn:r333|333]]</sup> . Such a transition depends on cities that enable modal shifts and avoided journeys and that provide incentives for uptake of improved fuel efficiency and changes in urban design that encourage walkable cities, non-motorized transport and shorter commuter distances (IEA, 2016a; Mittal et al., 2016; Zhang et al., 2016; Li and Loo, 2017) <sup>[[#fn:r334|334]]</sup> . In at least 4 African cities, 43 Asian cities and 54 Latin American cities, transit-oriented development (TOD), has emerged as an organizing principle for urban growth and spatial planning (Colenbrander et al., 2017; Lwasa, 2017; BRTData, 2018) <sup>[[#fn:r335|335]]</sup> . This trend is important to counter the rising demand for private cars in developing-country cities (AfDB/OECD/UNDP, 2016) <sup>[[#fn:r336|336]]</sup> . In India, TOD has been combined with localized solar PV installations and new ways of financing rail expansion (Sharma, 2018) <sup>[[#fn:r337|337]]</sup> .

Cities pursuing sustainable transport benefit from reduced air pollution, congestion and road fatalities and are able to harness the relationship between transport systems, urban form, urban energy intensity and social cohesion (Goodwin and Van Dender, 2013; Newman and Kenworthy, 2015; Wee, 2015) <sup>[[#fn:r338|338]]</sup> .

Technology and electrification trends since AR5 make carbon-efficient urban transport easier (Newman et al., 2016) <sup>[[#fn:r339|339]]</sup> , but realizing urban transport’s contribution to a 1.5°C-consistent pathways will require the type of governance that can overcome the financial, institutional, behavioural and legal barriers to change (Geels, 2014; Bakker et al., 2017) <sup>[[#fn:r340|340]]</sup> .

Adaptation to a 1.5°C world is enabled by urban design and spatial planning policies that consider extreme weather conditions and reduce displacement by climate related disasters (UNISDR, 2009; UN-Habitat, 2011; Mitlin and Satterthwaite, 2013) <sup>[[#fn:r341|341]]</sup> .

Building codes and technology standards for public lighting, including traffic lights (Beccali et al., 2015) <sup>[[#fn:r342|342]]</sup> , play a critical role in reducing carbon emissions, enhancing urban climate resilience and managing climate risk (Steenhof and Sparling, 2011; Parnell, 2015; Shapiro, 2016; Evans et al., 2017) <sup>[[#fn:r343|343]]</sup> . Building codes can support the convergence to zero emissions from buildings (Wells et al., 2018) <sup>[[#fn:r344|344]]</sup> and can be used retrofit the existing building stock for energy efficiency (Ruparathna et al., 2016) <sup>[[#fn:r345|345]]</sup> .

The application of building codes and standards for 1.5°C-consistent pathways will require improved enforcement, which can be a challenge in developing countries where inspection resources are often limited and codes are poorly tailored to local conditions (Ford et al., 2015c; Chandel et al., 2016; Eisenberg, 2016; Shapiro, 2016; Hess and Kelman, 2017; Mavhura et al., 2017) <sup>[[#fn:r346|346]]</sup> . In all countries, building codes can be undermined by industry interests and can be maladaptive if they prevent buildings or land use from evolving to reduce climate impacts (Eisenberg, 2016; Shapiro, 2016) <sup>[[#fn:r347|347]]</sup> .

The deficit in building codes and standards in middle-income and developing-country cities need not be a constraint to more energy-efficient and resilient buildings (Tait and Euston-Brown, 2017) <sup>[[#fn:r348|348]]</sup> . For example, the relatively high price that poor households pay for unreliable and at times dangerous household energy in African cities has driven the uptake of renewable energy and energy efficiency technologies in the absence of regulations or fiscal incentives (Eberhard et al., 2011, 2016; Cartwright, 2015; Watkins, 2015) <sup>[[#fn:r349|349]]</sup> . The Kuyasa Housing Project in Khayelitsha, one of Cape Town’s poorest suburbs, created significant mitigation and adaptation benefits by installing ceilings, solar water heaters and energy-efficient lightbulbs in houses independent of the formal housing or electrification programme (Winkler, 2017) <sup>[[#fn:r350|350]]</sup> .

<div id="section-4-3-3-4"></div>

<span id="electrification-of-cities-and-transport"></span>
==== 4.3.3.4 Electrification of cities and transport ====

<div id="section-4-3-3-4-block-1"></div>

The electrification of urban systems, including transport, has shown global progress since AR5 (IEA, 2016a; Kennedy et al., 2018; Schiller and Kenworthy, 2018) <sup>[[#fn:r351|351]]</sup> . High growth rates are now appearing in electric vehicles (Figure 4.1), electric bikes and electric transit (IEA, 2018) <sup>[[#fn:r352|352]]</sup> , which would need to displace fossil fuel-powered passenger vehicles by 2035–2050 to remain in line with 1.5°C-consistent pathways. China’s 2017 Road Map calls for 20% of new vehicle sales to be electric. India is aiming for exclusively electric vehicles (EVs) by 2032 (NITI Aayog and RMI, 2017) <sup>[[#fn:r353|353]]</sup> . Globally, EV sales were up 42% in 2016 relative to 2015, and in the United States EV sales were up 36% over the same period (Johnson and Walker, 2016) <sup>[[#fn:r354|354]]</sup> .

<div id="section-4-3-3-4-block-2"></div>

<span id="figure-4.1"></span>
<!-- START IMG -->
<!-- IMG TITLE -->
'''Figure 4.1'''

<span id="increase-of-the-global-electric-car-stock-by-country-20132017."></span>
<!-- IMG CAPTION -->
'''Increase of the global electric car stock by country (2013–2017).'''
<!-- IMG FILE -->
[[File:7a745c048d60a7c92d6bc6d3b4f1c107 fig-4.1-1024x588.jpg]]

The grey line is battery electric vehicles (BEV) only while the black line includes both BEV and plug-in hybrid vehicles (PHEV). Source: (IEA, 2018) <sup>[[#fn:r355|355]]</sup> . Based on IEA data from Global EV Outlook 2018 © OECD/IEA 2018, IEA Publishing.

<!-- END IMG -->
<div id="section-4-3-3-4-block-3"></div>

The extent of electric railways in and between cities has expanded since AR5 (IEA, 2016a; Mittal et al., 2016; Zhang et al., 2016; Li and Loo, 2017) <sup>[[#fn:r356|356]]</sup> . In high-income cities there is ''medium evidence'' for the decoupling of car use and wealth since AR5 (Newman, 2017) <sup>[[#fn:r357|357]]</sup> . In cities where private vehicle ownership is expected to increase, less carbon-intensive fuel sources and reduced car journeys will be necessary as well as electrification of all modes of transport (Mittal et al., 2016; van Vuuren et al., 2017) <sup>[[#fn:r358|358]]</sup> . Some recent urban data show a decoupling of urban growth and GHG emissions (Newman and Kenworthy, 2015) <sup>[[#fn:r359|359]]</sup> and that ‘peak car’ has been reached in Shanghai and Beijing (Gao and Kenworthy, 2017) <sup>[[#fn:r360|360]]</sup> and beyond (Manville et al., 2017) <sup>[[#fn:r361|361]]</sup> (also see Box 4.9).

An estimated 800 cities globally have operational bike-share schemes (E. Fishman et al., 2015) <sup>[[#fn:r362|362]]</sup> , and China had 250 million electric bicycles in 2017 (Newman et al., 2017) <sup>[[#fn:r363|363]]</sup> . Advances in information and communication technologies (ICT) offer cities the chance to reduce urban transport congestion and fuel consumption by making better use of the urban vehicle fleet through car sharing, driverless cars and coordinated public transport, especially when electrified (Wee, 2015; Glazebrook and Newman, 2018) <sup>[[#fn:r364|364]]</sup> . Advances in ‘big-data’ can assist in creating a better understanding of the connections between cities, green infrastructure, environmental services and health (Jennings et al., 2016) <sup>[[#fn:r365|365]]</sup> and improve decision-making in urban development (Lin et al., 2017) <sup>[[#fn:r366|366]]</sup> .

<div id="section-4-3-3-5"></div>

<span id="shipping-freight-and-aviation"></span>
==== 4.3.3.5 Shipping, freight and aviation ====

<div id="section-4-3-3-5-block-1"></div>

International transport hubs, including airports and ports, and the associated mobility of people are major economic contributors to most large cities even while under the governance of national authorities and international legislation. Shipping, freight and aviation systems have grown rapidly, and little progress has been made since AR5 on replacing fossil fuels, though some trials are continuing (Zhang, 2016; Bouman et al., 2017; EEA, 2017) <sup>[[#fn:r367|367]]</sup> . Aviation emissions do not yet feature in IAMs (Bows-Larkin, 2015) <sup>[[#fn:r368|368]]</sup> , but could be reduced by between a third and two-thirds through energy efficiency measures and operational changes (Dahlmann et al., 2016) <sup>[[#fn:r369|369]]</sup> . On shorter intercity trips, aviation could be replaced by high-speed electric trains drawing on renewable energy (Åkerman, 2011) <sup>[[#fn:r370|370]]</sup> . Some progress has been made on the use of electricity in planes and shipping (Grewe et al., 2017) <sup>[[#fn:r371|371]]</sup> though no commercial applications have arisen. Studies indicate that biofuels are the most viable means of decarbonizing intercontinental travel, given their technical characteristics, energy content and affordability (Wise et al., 2017) <sup>[[#fn:r372|372]]</sup> . The lifecycle emissions of bio-based jet fuels and marine fuels can be considerable (Cox et al., 2014; IEA, 2017g) <sup>[[#fn:r373|373]]</sup> depending on their location (Elshout et al., 2014) <sup>[[#fn:r374|374]]</sup> , but can be reduced by feedstock and conversion technology choices (de Jong et al., 2017) <sup>[[#fn:r375|375]]</sup> .

In recent years the potential for transport to use synfuels, such as ethanol, methanol, methane, ammonia and hydrogen, created from renewable electricity and CO <sub>2</sub> , has gained momentum but has not yet demonstrated benefits on a scale consistent with 1.5°C pathways (Ezeji, 2017; Fasihi et al., 2017) <sup>[[#fn:r376|376]]</sup> . Decarbonizing the fuel used by the world’s 60,000 large ocean vessels faces governance barriers and the need for a global policy (Bows and Smith, 2012; IRENA, 2015; Rehmatulla and Smith, 2015) <sup>[[#fn:r377|377]]</sup> . Low-emission marine fuels could simultaneously address sulphur and black carbon issues in ports and around waterways and accelerate the electrification of all large ports (Bouman et al., 2017; IEA, 2017g) <sup>[[#fn:r378|378]]</sup> .

<div id="section-4-3-3-x"></div>

<span id="climate-resilient-land-use"></span>
==== 4.3.3.6 Climate-resilient land use ====

<div id="section-4-3-3-x-block-1"></div>

Urban land use influences energy intensity, risk exposure and adaptive capacity (Carter et al., 2015; Araos et al., 2016a; Ewing et al., 2016; Newman et al., 2016; Broto, 2017) <sup>[[#fn:r379|379]]</sup> . Accordingly, urban land-use planning can contribute to climate mitigation and adaptation (Parnell, 2015; Francesch-Huidobro et al., 2017) <sup>[[#fn:r380|380]]</sup> and the growing number of urban climate adaptation plans provide instruments to do this (Carter et al., 2015; Dhar and Khirfan, 2017; Siders, 2017; Stults and Woodruff, 2017) <sup>[[#fn:r381|381]]</sup> . Adaptation plans can reduce exposure to urban flood risk (which, in a 1.5°C world, could double relative to 1976–2005; Alfieri et al., 2017) <sup>[[#fn:r382|382]]</sup> , heat stress (Chapter 3, Section 3.5.5.8), fire risk (Chapter 3, Section 3.4.3.4) and sea level rise (Chapter 3,

Section 3.4.5.1) (Schleussner et al., 2016) <sup>[[#fn:r383|383]]</sup> .

Cities can reduce their risk exposure by considering investment in infrastructure and buildings that are more resilient to warming of 1.5°C or beyond. Where adaptation planning and urban planning generate the type of local participation that enhances capacity to cope with risks, they can be mutually supportive processes  (Archer et al., 2014; Kettle et al., 2014; Campos et al., 2016; Chu et al., 2017; Siders, 2017; Underwood et al., 2017) <sup>[[#fn:r384|384]]</sup> . Not all adaptation plans are reported as effective (Measham et al., 2011; Hetz, 2016; Woodruff and Stults, 2016; Mahlkow and Donner, 2017) <sup>[[#fn:r385|385]]</sup> , especially in developing-country cities (Kiunsi, 2013) <sup>[[#fn:r386|386]]</sup> . In cases where adaptation planning may further marginalize poor citizens, either through limited local control over adaptation priorities or by displacing impacts onto poorer communities, successful urban risk management would need to consider factors such as justice, equity, and inclusive participation, as well as recognize the political economy of adaptation (Archer, 2016; Shi et al., 2016; Ziervogel et al., 2016a, 2017; Chu et al., 2017) <sup>[[#fn:r387|387]]</sup> .

<div id="section-4-3-3-7"></div>

<span id="green-urban-infrastructure-and-ecosystem-services"></span>
==== 4.3.3.7 Green urban infrastructure and ecosystem services ====

<div id="section-4-3-3-7-block-1"></div>

Integrating and promoting green urban infrastructure (including street trees, parks, green roofs and facades, and water features) into city planning can be difficult (Leck et al., 2015) <sup>[[#fn:r388|388]]</sup> but increases urban resilience to impacts of 1.5°C warming (Table 4.2) in ways that can be more cost-effective than conventional infrastructure (Cartwright et al., 2013; Culwick and Bobbins, 2016) <sup>[[#fn:r389|389]]</sup> .

<div id="section-4-3-3-7-block-2"></div>

<span id="table-4.2"></span>
<!-- START TABLE -->
'''Table 4.2'''

<span id="green-urban-infrastructure-and-benefits"></span>
'''Green urban infrastructure and benefits'''

<!-- TABLE -->
{| class="wikitable"
|-
! Green<br />
Infrastructure
! Adaptation<br />
Benefits
! Mitigation<br />
Benefits
! References
|-
| Urban tree planting,<br />
urban parks
| Reduced heat island effect, psychological benefits
| Less cement, reduced air-conditioning use
| Demuzere et al., 2014; Mullaney et al., 2015; Soderlund and Newman, 2015; Beaudoin and Gosselin, 2016; Green et al., 2016; Lin et al., 2017 <sup>[[#fn:r390|390]]</sup>
|-
| Permeable surfaces
| Water recharge
| Less cement in city, some bio-sequestration, less water pumping
| Liu et al., 2014; Lamond et al., 2015; Skougaard Kaspersen et al., 2015; Voskamp and Van de Ven, 2015; Costa et al., 2016; Mguni et al., 2016; Xie et al., 2017 <sup>[[#fn:r391|391]]</sup>
|-
| Forest retention, urban agricultural land
| Flood mediation, healthy lifestyles
| Reduced air pollution
| Nowak et al., 2006; Tallis et al., 2011; Elmqvist et al., 2013; Buckeridge, 2015; Culwick and Bobbins, 2016; Panagopoulos et al., 2016; Stevenson et al., 2016; R. White et al., 2017 <sup>[[#fn:r392|392]]</sup>
|-
| Wetland restoration, riparian buffer zones
| Reduced urban flooding, low-skilled local work, sense of place
| Some bio-sequestration,<br />
less energy spent on water treatment
| Cartwright et al., 2013; Elmqvist et al., 2015; Brown and McGranahan, 2016; Camps-Calvet et al., 2016; Culwick and Bobbins, 2016; McPhearson et al., 2016; Ziervogel et al., 2016b; Collas et al., 2017; F. Li et al., 2017 <sup>[[#fn:r393|393]]</sup>
|-
| Biodiverse urban habitat
| Psychological benefits, inner-city recreation
| Carbon sequestration
| Beatley, 2011; Elmqvist et al., 2015; Brown and McGranahan, 2016; Camps-Calvet et al., 2016; McPhearson et al., 2016; Collas et al., 2017; F. Li et al., 2017 <sup>[[#fn:r394|394]]</sup>
|}
<!-- END TABLE -->

<div id="section-4-3-3-7-block-3"></div>

Realizing climate benefits from urban green infrastructure sometimes requires a city-region perspective (Wachsmuth et al., 2016) <sup>[[#fn:r395|395]]</sup> . Where the urban impact on ecological systems in and beyond the city is appreciated, the potential for transformative change exists (Soderlund and Newman, 2015; Ziervogel et al., 2016a) <sup>[[#fn:r396|396]]</sup> , and a locally appropriate combination of green space, ecosystem goods and services and the built environment can increase the set of urban adaptation options (Puppim de Oliveira et al., 2013) <sup>[[#fn:r397|397]]</sup> .

Milan, Italy, a city with deliberate urban greening policies, planted 10,000 hectares of new forest and green areas over the last two decades (Sanesi et al., 2017) <sup>[[#fn:r398|398]]</sup> . The accelerated growth of urban trees, relative to rural trees, in several regions of the world is expected to decrease tree longevity (Pretzsch et al., 2017) <sup>[[#fn:r399|399]]</sup> , requiring monitoring and additional management of urban trees if their contribution to urban ecosystem-based adaptation and mitigation is to be maintained in a 1.5°C world (Buckeridge, 2015; Pretzsch et al., 2017) <sup>[[#fn:r400|400]]</sup> .

<div id="section-4-3-3-8-2"></div>

<span id="sustainable-urban-water-and-environmental-services"></span>
==== 4.3.3.8 Sustainable urban water and environmental services ====

<div id="section-4-3-3-8-2-block-1"></div>

Urban water supply and wastewater treatment is energy intensive and currently accounts for significant GHG emissions (Nair et al., 2014) <sup>[[#fn:r401|401]]</sup> . Cities can integrate sustainable water resource management and the supply of water services in ways that support mitigation, adaptation and development through waste water recycling and storm water diversion (Xue et al., 2015; Poff et al., 2016) <sup>[[#fn:r402|402]]</sup> . Governance and finance challenges complicate balancing sustainable water supply and rising urban demand, particularly in low-income cities (Bettini et al., 2015; Deng and Zhao, 2015; Hill Clarvis and Engle, 2015; Lemos, 2015; Margerum and Robinson, 2015) <sup>[[#fn:r403|403]]</sup> .

Urban surface-sealing with impervious materials affects the volume and velocity of runoff and flooding during intense rainfall (Skougaard Kaspersen et al., 2015) <sup>[[#fn:r404|404]]</sup> , but urban design in many cities now seeks to mediate runoff, encourage groundwater recharge and enhance water quality (Liu et al., 2014; Lamond et al., 2015; Voskamp and Van de Ven, 2015; Costa et al., 2016; Mguni et al., 2016; Xie et al., 2017) <sup>[[#fn:r405|405]]</sup> . Challenges remain for managing intense rainfall events that are reported to be increasing in frequency and intensity in some locations (Ziervogel et al., 2016b) <sup>[[#fn:r406|406]]</sup> , and urban flooding is expected to increase at 1.5°C of warming (Alfieri et al., 2017) <sup>[[#fn:r407|407]]</sup> . This risk falls disproportionately on women and poor people in cities (Mitlin, 2005; Chu et al., 2016; Ziervogel et al., 2016b; Chant et al., 2017; Dodman et al., 2017a, b) <sup>[[#fn:r408|408]]</sup> .

Nexus approaches that highlight urban areas as socio-ecological systems can support policy coherence (Rasul and Sharma, 2016) <sup>[[#fn:r409|409]]</sup> and sustainable urban livelihoods (Biggs et al., 2015) <sup>[[#fn:r410|410]]</sup> . The water–energy–food (WEF) nexus is especially important to growing urban populations (Tacoli et al., 2013; Lwasa et al., 2014; Villarroel Walker et al., 2014) <sup>[[#fn:r411|411]]</sup> .

<span id="industrial-systems-transitions"></span>
=== 4.3.4 Industrial Systems Transitions ===

<div id="section-4-3-4-block-1"></div>

Industry consumes about one-third of global final energy and contributes, directly and indirectly, about one-third of global GHG emissions (IPCC, 2014b) <sup>[[#fn:r412|412]]</sup> . If the increase in global mean temperature is to remain under 1.5°C, modelling indicates that industry cannot emit more than 2 GtCO <sub>2</sub> in 2050, corresponding to a reduction of between 67 and 91% (interquartile range) in GHG emissions compared to 2010 (see Chapter 2, Figures 2.20 and 2.21 and Table 4.1). Moreover, the consequences of warming of 1.5°C or more pose substantial challenges for industrial diversity. This section will first briefly discuss the limited literature on adaptation options for industry. Subsequently, new literature since AR5 on the feasibility of industrial mitigation options will be discussed.

Research assessing adaptation actions by industry indicates that only a small fraction of corporations has developed adaptation measures. Studies of adaptation in the private sector remain limited (Agrawala et al., 2011; Linnenluecke et al., 2015; Averchenkova et al., 2016; Bremer and Linnenluecke, 2016; Pauw et al., 2016a) <sup>[[#fn:r413|413]]</sup> and for 1.5°C are largely absent. This knowledge gap is particularly evident for medium-sized enterprises and in low- and middle-income nations (Surminski, 2013) <sup>[[#fn:r414|414]]</sup> .

Depending on the industrial sector, mitigation consistent with 1.5°C would mean, across industries, a reduction of final energy demand by one-third, an increase of the rate of recycling of materials and the development of a circular economy in industry (Lewandowski, 2016; Linder and Williander, 2017) <sup>[[#fn:r415|415]]</sup> , the substitution of materials in high-carbon products with those made up of renewable materials (e.g., wood instead of steel or cement in the construction sector, natural textile fibres instead of plastics), and a range of deep emission reduction options, including use of bio-based feedstocks, low-emission heat sources, electrification of production processes, and/or capture and storage of all CO <sub>2</sub> emissions by 2050 (Åhman et al., 2016) <sup>[[#fn:r416|416]]</sup> . Some of the choices for mitigation options and routes for GHG-intensive industry are discrete and potentially subject to path dependency: if an industry goes one way (e.g., in keeping existing processes), it will be harder to transition to process change (e.g., electrification) (Bataille et al., 2018) <sup>[[#fn:r417|417]]</sup> . In the context of rising demand for construction, an increasing share of industrial production may be based in developing countries (N. Li et al., 2017) <sup>[[#fn:r418|418]]</sup> , where current efficiencies may be lower than in developed countries, and technical and institutional feasibility may differ (Ma et al., 2015) <sup>[[#fn:r419|419]]</sup> .

Except for energy efficiency, costs of disruptive change associated with hydrogen- or electricity-based production, bio-based feedstocks and carbon dioxide capture, (utilization) and storage (CC(U)S) for trade-sensitive industrial sectors (in particular the iron and steel, petrochemical and refining industries) make policy action by individual countries challenging because of competitiveness concerns (Åhman et al., 2016; Nabernegg et al., 2017) <sup>[[#fn:r420|420]]</sup> .

Table 4.3 provides an overview of applicable mitigation options for key industrial sectors.

<div id="section-4-3-4-block-2"></div>

<span id="table-4.3"></span>
<!-- START TABLE -->
'''Table 4.3'''

Overview of different mitigation options potentially consistent with limiting warming to 1.5°C and applicable to main industrial sectors, including examples of application (Napp et al., 2014; Boulamanti and Moya, 2017; Wesseling et al., 2017) <sup>[[#fn:r421|421]]</sup> .

<!-- TABLE -->
{| class="wikitable"
|-
| '''Industrial mitigation option'''
| '''Iron/Steel'''
| '''Cement'''
| '''Refineries and'''<br />
'''Petrochemicals'''
| '''Chemicals'''
|-
| Process and Energy Efficiency
| colspan="4"| Can make a difference of between 10% and 50%, depending on the plant. Relevant but not enough for 1.5°C
|-
| Bio-based
| Coke can be made from biomass<br />
instead of coal
| Partial (only energy-related<br />
emissions)
| colspan="2"| Biomass can replace fossil feedstocks
|-
| Circularity &amp; Substitution
| colspan="2"| More recycling and replacement by low-emission materials,
including alternative chemistries for cement

| colspan="2"| Limited potential
|-
| Electrification &amp; Hydrogen
| Direct reduction with hydrogen.<br />
Heat generation through electricity
| Partial (only electrified heat<br />
generation)
| colspan="2"| Electrified heat and hydrogen generation
|-
| Carbon dioxide capture, utilization and storage
| colspan="2"| Possible for process emissions and energy. Reduces emissions by 80–95%, and net emissions can become negative when combined with biofuel
| colspan="2"| Can be applied to energy emissions and different stacks but not on<br />
emissions of products in the use phase (e.g., gasoline)
|}
<!-- END TABLE -->

<div id="section-4-3-4-1"></div>

<span id="energy-efficiency"></span>
==== 4.3.4.1 Energy efficiency ====

<div id="section-4-3-4-1-block-1"></div>

Isolated efficiency implementation in energy-intensive industries is a necessary but insufficient condition for deep emission reductions (Napp et al., 2014; Aden, 2018) <sup>[[#fn:r422|422]]</sup> . Various options specific to different industries are available. In general, their feasibility depends on lowering capital costs and raising awareness and expertise (Wesseling et al., 2017) <sup>[[#fn:r423|423]]</sup> . General-purpose technologies, such as ICT, and energy management tools can improve the prospects of energy efficiency in industry (see Section 4.4.4).

Cross-sector technologies and practices, which play a role in all industrial sectors including small- and medium-sized enterprises (SMEs) and non-energy intensive industry, also offer potential for considerable energy efficiency improvements. They include: (i) motor systems (for example electric motors, variable speed drives, pumps, compressors and fans), responsible for about 10% of worldwide industrial energy consumption, with a global energy efficiency improvement potential of around 20–25% (Napp et al., 2014) <sup>[[#fn:r424|424]]</sup> ; and (ii) steam systems, responsible for about 30% of industrial energy consumption and energy saving potentials of about 10% (Hasanbeigi et al., 2014; Napp et al., 2014) <sup>[[#fn:r425|425]]</sup> . Waste heat recovery from industry has substantial potential for energy efficiency and emission reduction (Forman et al., 2016) <sup>[[#fn:r426|426]]</sup> . Low awareness and competition from other investments limit the feasibility of such options (Napp et al., 2014) <sup>[[#fn:r427|427]]</sup> .

<div id="section-4-3-4-2"></div>

<span id="substitution-and-circularity"></span>
==== 4.3.4.2 Substitution and circularity ====

<div id="section-4-3-4-2-block-1"></div>

Recycling materials and developing a circular economy can be institutionally challenging, as it requires advanced capabilities (Henry et al., 2006) <sup>[[#fn:r428|428]]</sup> and organizational changes (Cooper-Searle et al., 2018) <sup>[[#fn:r429|429]]</sup> , but has advantages in terms of cost, health, governance and environment (Ali et al., 2017) <sup>[[#fn:r430|430]]</sup> . An assessment of the impacts on energy use and environmental issues is not available, but substitution could play a large role in reducing emissions (Åhman et al., 2016) <sup>[[#fn:r431|431]]</sup> although its potential depends on the demand for material and the turnover rate of, for example, buildings (Haas et al., 2015) <sup>[[#fn:r432|432]]</sup> . Material substitution and CO <sub>2</sub> storage options are under development, for example, the use of algae and renewable energy for carbon fibre production, which could become a net sink of CO <sub>2</sub> (Arnold et al., 2018) <sup>[[#fn:r433|433]]</sup> .

<div id="section-4-3-4-3"></div>

<span id="bio-based-feedstocks"></span>
==== 4.3.4.3 Bio-based feedstocks ====

<div id="section-4-3-4-3-block-1"></div>

Bio-based feedstock processes could be seen as part of the circular materials economy (see section above). In several sectors, bio-based feedstocks would leave the production process of materials relatively untouched, and a switch would not affect the product quality, making the option more attractive. However, energy requirements for processing bio-based feedstocks are often high, costs are also still higher, and the emissions over the full life cycle, both upstream and downstream, could be significant (Wesseling et al., 2017) <sup>[[#fn:r434|434]]</sup> . Bio-based feedstocks may put pressure on natural resources by increasing land demand by biodiversity impacts beyond bioenergy demand for electricity, transport and buildings (Slade et al., 2014) <sup>[[#fn:r435|435]]</sup> , and, partly as a result, face barriers in public acceptance (Sleenhoff et al., 2015) <sup>[[#fn:r436|436]]</sup> .

<div id="section-4-3-4-4"></div>

<span id="electrification-and-hydrogen"></span>
==== 4.3.4.4 Electrification and hydrogen ====

<div id="section-4-3-4-4-block-1"></div>

Electrification of manufacturing processes would constitute a significant technological challenge and would entail a more disruptive innovation in industry than bio-based or CCS options to get to very low or zero emissions, except potentially in steel-making (Philibert, 2017) <sup>[[#fn:r437|437]]</sup> . The disruptive characteristics could potentially lead to stranded assets, and could reduce political feasibility and industry support (Åhman et al., 2016) <sup>[[#fn:r438|438]]</sup> . Electrification of manufacturing would require further technological development in industry, as well as an ample supply of cost-effective low-emission electricity (Philibert, 2017) <sup>[[#fn:r439|439]]</sup> .

Low-emission hydrogen can be produced by natural gas with CCS, by electrolysis of water powered by zero-emission electricity, or potentially in the future by generation IV nuclear reactors. Feasibility of electrification and use of hydrogen in production processes or fuel cells is affected by technical development (in terms of efficient hydrogen production and electrification of processes), by geophysical factors related to the availability of low-emission electricity (MacKay, 2013) <sup>[[#fn:r440|440]]</sup> , by associated public perception and by economic feasibility, except in areas with ample solar and/or wind resources (Philibert, 2017; Wesseling et al., 2017) <sup>[[#fn:r441|441]]</sup> .

<div id="section-4-3-4-5"></div>

<span id="co2-capture-utilization-and-storage-in-industry"></span>
==== 4.3.4.5 CO2 capture, utilization and storage in industry ====

<div id="section-4-3-4-5-block-1"></div>

CO <sub>2</sub> capture in industry is generally considered more feasible than CCS in the power sector (Section 4.3.1) or from bioenergy sources (Section 4.3.7), although CCS in industry faces similar barriers. Almost all of the current full-scale (&gt;1MtCO <sub>2</sub> yr <sup>−1</sup> ) CCS projects capture CO <sub>2</sub> from industrial sources, including the Sleipner project in Norway, which has been injecting CO <sub>2</sub> from a gas facility in an offshore saline formation since 1996 (Global CCS Institute, 2017) <sup>[[#fn:r442|442]]</sup> . Compared to the power sector, retrofitting CCS on existing industrial plants would leave the production process of materials relatively untouched (Åhman et al., 2016) <sup>[[#fn:r443|443]]</sup> , though significant investments and modifications still have to be made. Some industries, in particular cement, emit CO <sub>2</sub> as inherent process emissions and can therefore not reduce emissions to zero without CC(U)S. CO <sub>2</sub> stacks in some industries have a high economic and technical feasibility for CO <sub>2</sub> capture as the CO <sub>2</sub> concentration in the exhaust gases is relatively high (IPCC, 2005b; Leeson et al., 2017) <sup>[[#fn:r444|444]]</sup> , but others require strong modifications in the production process, limiting technical and economic feasibility, though costs remain lower than other deep GHG reduction options (Rubin et al., 2015) <sup>[[#fn:r445|445]]</sup> . There are indications that the energy use in CO <sub>2</sub> capture through amine solvents (for solvent regeneration) can decrease by around 60%, from 5 GJ tCO <sub>2</sub> <sup>−</sup> <sup>1</sup> in 2005 to 2 GJ tCO <sub>2</sub> <sup>−</sup> <sup>1</sup> in the best-performing current pilot plants (Idem et al., 2015) <sup>[[#fn:r446|446]]</sup> , increasing both technical and economic potential for this option. The heterogeneity of industrial production processes might point to the need for specific institutional arrangements to incentivize industrial CCS (Mikunda et al., 2014) <sup>[[#fn:r447|447]]</sup> , and may decrease institutional feasibility.

Whether carbon dioxide utilization (CCU) can contribute to limiting warming to 1.5°C depends on the origin of the CO <sub>2</sub> (fossil, biogenic or atmospheric), the source of electricity for converting the CO <sub>2</sub> or regenerating catalysts, and the lifetime of the product. Review studies indicate that CO <sub>2</sub> utilization in industry has a small role to play in limiting warming to 1.5°C because of the limited potential of reusing CO <sub>2</sub> with currently available technologies and the re-emission of CO <sub>2</sub> when used as a fuel (IPCC, 2005b; Mac Dowell et al., 2017) <sup>[[#fn:r448|448]]</sup> . However, new developments could make CCU more feasible, in particular in CO <sub>2</sub> use as a feedstock for carbon-based materials that would isolate CO <sub>2</sub> from the atmosphere for a long time, and in low-cost, low-emission electricity that would make the energy use of CO <sub>2</sub> capture more sustainable. The conversion of CO <sub>2</sub> to fuels using zero-emission electricity has a lower technical, economic and environmental feasibility than direct CO <sub>2</sub> capture and storage from industry (Abanades et al., 2017) <sup>[[#fn:r449|449]]</sup> , although the economic prospects have improved recently (Philibert, 2017) <sup>[[#fn:r450|450]]</sup> .

<span id="overarching-adaptation-options-supporting-adaptation-transitions"></span>
=== 4.3.5 Overarching Adaptation Options Supporting Adaptation Transitions ===

<div id="section-4-3-5-block-1"></div>

This section assesses overarching adaptation options –specific solutions from which actors can choose and make decisions to reduce climate vulnerability and build resilience. We examine their feasibility in the context of transitions of energy, land and ecosystem, urban and infrastructure, and industrial systems here, and further in Section 4.5. These options can contribute to creating an enabling environment for adaptation (see Table 4.4 and Section 4.4).

<div id="section-4-3-5-1"></div>

<span id="disaster-risk-management-drm"></span>
==== 4.3.5.1 Disaster risk management (DRM) ====

<div id="section-4-3-5-1-block-1"></div>

DRM is a process for designing, implementing and evaluating strategies, policies and measures to improve the understanding of disaster risk, and promoting improvement in disaster preparedness, response and recovery (IPCC, 2012) <sup>[[#fn:r451|451]]</sup> . There is increased demand to integrate DRM and adaptation (Howes et al., 2015; Kelman et al., 2015; Serrao-Neumann et al., 2015; Archer, 2016; Rose, 2016; van der Keur et al., 2016; Kelman, 2017; Wallace, 2017) <sup>[[#fn:r452|452]]</sup> to reduce vulnerability, but institutional, technical and financial capacity challenges in frontline agencies constitute constraints ( ''medium evidence, high agreement'' ) (Eakin et al., 2015; Kita, 2017; Wallace, 2017) <sup>[[#fn:r453|453]]</sup> .

<div id="section-4-3-5-2"></div>

<span id="risk-sharing-and-spreading"></span>
==== 4.3.5.2 Risk sharing and spreading ====

<div id="section-4-3-5-2-block-1"></div>

Risks associated with 1.5ºC warming (Chapter 3, Section 3.4) may increase the demand for options that share and spread financial burdens. Formal, market-based (re)insurance spreads risk and provides a financial buffer against the impacts of climate hazards (Linnerooth-Bayer and Hochrainer-Stigler, 2015; Wolfrom and Yokoi-Arai, 2015; O’Hare et al., 2016; Glaas et al., 2017; Patel et al., 2017) <sup>[[#fn:r454|454]]</sup> . As an alternative to traditional indemnity-based insurance, index-based micro-crop and livestock insurance programmes have been rolled out in regions with less developed insurance markets (Akter et al., 2016, 2017; Jensen and Barrett, 2017) <sup>[[#fn:r455|455]]</sup> . There is ''medium evidence'' and ''medium agreement'' on the feasibility of insurance for adaptation, with financial, social, and institutional barriers to implementation and uptake, especially in low-income nations (García Romero and Molina, 2015; Joyette et al., 2015; Lashley and Warner, 2015; Jin et al., 2016) <sup>[[#fn:r456|456]]</sup> . Social protection programmes include cash and in-kind transfers to protect poor and vulnerable households from the impact of economic shocks, natural disasters and other crises (World Bank, 2017b) <sup>[[#fn:r457|457]]</sup> , and can build generic adaptive capacity and reduce vulnerability when combined with a comprehensive climate risk management approach ( ''medium evidence'' , ''medium agreement'' ) (Devereux, 2016; Lemos et al., 2016) <sup>[[#fn:r458|458]]</sup> .

<div id="section-4-3-5-3"></div>

<span id="education-and-learning"></span>
==== 4.3.5.3 Education and learning ====

<div id="section-4-3-5-3-block-1"></div>

Educational adaptation options motivate adaptation through building awareness (Butler et al., 2016; Myers et al., 2017) <sup>[[#fn:r459|459]]</sup> , leveraging multiple knowledge systems (Pearce et al., 2015; Janif et al., 2016) <sup>[[#fn:r460|460]]</sup> , developing participatory action research and social learning processes (Butler and Adamowski, 2015; Ensor and Harvey, 2015; Butler et al., 2016; Thi Hong Phuong et al., 2017; Ford et al., 2018) <sup>[[#fn:r461|461]]</sup> , strengthening extension services, and building mechanisms for learning and knowledge sharing through community-based platforms, international conferences and knowledge networks (Vinke-de Kruijf and Pahl-Wostl, 2016) <sup>[[#fn:r462|462]]</sup> ( ''medium evidence'' , ''high agreement'' ).

<div id="section-4-3-5-4"></div>

<span id="population-health-and-health-system-adaptation-options"></span>
==== 4.3.5.4 Population health and health system adaptation options ====

<div id="section-4-3-5-4-block-1"></div>

Climate change will exacerbate existing health challenges (Chapter 3, Section 3.4.7). Options for enhancing current health services include providing access to safe water and improved sanitation, enhancing access to essential services such as vaccination, and developing or strengthening integrated surveillance systems (WHO, 2015) <sup>[[#fn:r463|463]]</sup> . Combining these with iterative management can facilitate effective adaptation ( ''medium evidence'' , ''high agreement'' ).

<div id="section-4-3-5-5"></div>

<span id="indigenous-knowledge"></span>
==== 4.3.5.5 Indigenous knowledge ====

<div id="section-4-3-5-5-block-1"></div>

There is ''medium evidence'' and ''high agreement'' that indigenous knowledge is critical for adaptation, underpinning adaptive capacity through the diversity of indigenous agro-ecological and forest management systems, collective social memory, repository of accumulated experience and social networks (Hiwasaki et al., 2015; Pearce et al., 2015; Mapfumo et al., 2016; Sherman et al., 2016; Ingty, 2017) <sup>[[#fn:r464|464]]</sup> (Box 4.3). Indigenous knowledge is threatened by acculturation, dispossession of land rights and land grabbing, rapid environmental changes, colonization and social change, resulting in increasing vulnerability to climate change – which climate policy can exacerbate if based on limited understanding of indigenous worldviews (Thornton and Manasfi, 2010; Ford, 2012; Nakashima et al., 2012; McNamara and Prasad, 2014) <sup>[[#fn:r465|465]]</sup> . Many scholars argue that recognition of indigenous rights, governance systems and laws is central to adaptation, mitigation and sustainable development (Magni, 2017; Thornton and Comberti, 2017; Pearce, 2018) <sup>[[#fn:r466|466]]</sup> .

<div id="section-4-3-5-6"></div>

<span id="human-migration"></span>
==== 4.3.5.6 Human migration ====

<div id="section-4-3-5-6-block-1"></div>

Human migration, whether planned, forced or voluntary, is increasingly gaining attention as a response, particularly where climatic risks are becoming severe (Chapter 3, Section 3.4.10.2). There is ''medium'' ''evidence'' and ''low agreement'' as to whether migration is adaptive, in relation to cost effectiveness concerns (Grecequet et al., 2017) <sup>[[#fn:r467|467]]</sup> and scalability (Brzoska and Fröhlich, 2016; Gemenne and Blocher, 2017; Grecequet et al., 2017) <sup>[[#fn:r468|468]]</sup> . Migrating can have mixed outcomes on reducing socio-economic vulnerability (Birk and Rasmussen, 2014; Kothari, 2014; Adger et al., 2015; Betzold, 2015; Kelman, 2015; Grecequet et al., 2017; Melde et al., 2017; World Bank, 2017a; Kumari Rigaud et al., 2018) <sup>[[#fn:r469|469]]</sup> and its feasibility is constrained by low political and legal acceptability and inadequate institutional capacity (Betzold, 2015; Methmann and Oels, 2015; Brzoska and Fröhlich, 2016; Gemenne and Blocher, 2017; Grecequet et al., 2017; Yamamoto et al., 2017) <sup>[[#fn:r470|470]]</sup> .

<div id="section-4-3-5-7"></div>

<span id="climate-services"></span>
==== 4.3.5.7 Climate services ====

<div id="section-4-3-5-7-block-1"></div>

There is ''medium evidence'' and ''high agreement'' that climate services can play a critical role in aiding adaptation decision-making (Vaughan and Dessai, 2014; Wood et al., 2014; Lourenço et al., 2016; Trenberth et al., 2016; Singh et al., 2017; Vaughan et al., 2018) <sup>[[#fn:r471|471]]</sup> . The higher uptake of short-term climate information such as weather advisories and daily forecasts contrast with lesser use of longer-term information such as seasonal forecasts and multi-decadal projections (Singh et al., 2017; Vaughan et al., 2018) <sup>[[#fn:r472|472]]</sup> . Climate service interventions have met challenges with scaling up due to low capacity, inadequate institutions, and difficulties in maintaining systems beyond pilot project stage (Sivakumar et al., 2014; Tall et al., 2014; Gebru et al., 2015; Singh et al., 2016b) <sup>[[#fn:r473|473]]</sup> , and technical, institutional, design, financial and capacity barriers to the application of climate information for better decision-making remain (Briley et al., 2015; WMO, 2015; L. Jones et al., 2016; Lourenço et al., 2016; Snow et al., 2016; Harjanne, 2017; Singh et al., 2017; C.J. White et al., 2017) <sup>[[#fn:r474|474]]</sup> .

<div id="section-4-3-5-7-block-2"></div>

<span id="table-4.4"></span>
<!-- START TABLE -->
'''Table 4.4'''

<span id="assessment-of-overarching-adaptation-options-in-relation-to-enabling-conditions.-for-more-details-see-supplementary-material-4.sm.2."></span>
'''Assessment of overarching adaptation options in relation to enabling conditions. For more details, see Supplementary Material 4.SM.2.'''

<!-- TABLE -->
{| class="wikitable"
|-
! Option
! Enabling Conditions
! Examples
|-
| Disaster risk management (DRM)
| Governance and institutional capacity: supports post-disaster recovery and reconstruction (Kelman et al., 2015; Kull et al., 2016) <sup>[[#fn:r475|475]]</sup> .
| Early warning systems (Anacona et al., 2015) <sup>[[#fn:r476|476]]</sup> , and monitoring of dangerous lakes and surrounding slopes (including using remote sensing) offer DRM opportunities<br />
(Emmer et al., 2016; Milner et al., 2017) <sup>[[#fn:r477|477]]</sup> .
|-
| Risk sharing and spreading: insurance
| Institutional capacity and finance: buffers climate risk (Wolfrom and Yokoi-Arai, 2015; O’Hare et al., 2016; Glaas et al., 2017; Jenkins et al., 2017; Patel et al., 2017) <sup>[[#fn:r478|478]]</sup> .
| In 2007, the Caribbean Catastrophe Risk Insurance Facility was formed to pool risk from tropical cyclones, earthquakes, and excess rainfalls (Murphy et al., 2012; CCRIF, 2017) <sup>[[#fn:r479|479]]</sup> .
|-
| Social safety nets
| Institutional capacity and finance: builds generic adaptive capacity and reduces social vulnerability (Weldegebriel and Prowse, 2013; Eakin et al., 2014; Lemos et al., 2016; Schwan and Yu, 2017) <sup>[[#fn:r480|480]]</sup> .
| In sub-Saharan Africa, cash transfer programmes targeting poor communities have proven successful in smoothing household welfare and food security during droughts, strengthening community ties, and reducing debt levels (del Ninno et al., 2016; Asfaw et al., 2017; Asfaw and Davis, 2018) <sup>[[#fn:r481|481]]</sup> .
|-
| Education and learning
| Behavioural change and institutional capacity: social learning strengthens adaptation and affects longer-term change (Clemens et al., 2015; Ensor and Harvey, 2015; Henly-Shepard et al., 2015) <sup>[[#fn:r482|482]]</sup> .
| Participatory scenario planning is a process by which multiple stakeholders work together<br />
to envision future scenarios under a range of climatic conditions (Oteros-Rozas et al.,<br />
2015; Butler et al., 2016; Flynn et al., 2018) <sup>[[#fn:r483|483]]</sup> .
|-
| Population health and health system
| Institutional capacity: 1.5°C warming will primarily exacerbate existing health challenges (K.R. Smith et al., 2014) <sup>[[#fn:r484|484]]</sup> , which can be targeted by enhancing health services.
| Heatwave early warning and response systems coordinate the implementation of multiple measures in response to predicted extreme temperatures (e.g., public announcements, opening public cooling shelters, distributing information on heat stress symptoms) (Knowlton et al., 2014; Takahashi et al., 2015; Nitschke et al., 2016, 2017) <sup>[[#fn:r485|485]]</sup> .
|-
| Indigenous knowledge
| Institutional capacity and behavioural change: knowledge of environmental conditions helps communities detect and monitor change (Johnson et al., 2015; Mistry and Berardi, 2016; Williams et al., 2017) <sup>[[#fn:r486|486]]</sup> .
| Options such as integration of indigenous knowledge into resource management systems and school curricula, are identified as potential adaptations (Cunsolo Willox et al., 2013; McNamara and Prasad, 2014; MacDonald et al., 2015; Pearce et al., 2015; Chambers et al., 2017; Inamara and Thomas, 2017) <sup>[[#fn:r487|487]]</sup> .
|-
| Human migration
| Governance: revising and adopting migration issues in national disaster risk management policies, National Adaptation Plans and NDCs (Kuruppu and Willie, 2015; Yamamoto et al., 2017) <sup>[[#fn:r488|488]]</sup> .
| In dryland India, populations in rural regions already experiencing 1.5°C warming are migrating to cities (Gajjar et al., 2018)  <sup>[[#fn:r489|489]]</sup> but are inadequately covered by existing policies (Bhagat, 2017) <sup>[[#fn:r490|490]]</sup> .
|-
| Climate services
| Technological innovation: rapid technical development (due to increased financial inputs and growing demand) is improving quality of climate information provided (Rogers and Tsirkunov, 2010; Clements et al., 2013; Perrels et al., 2013; Gasc et al., 2014; WMO, 2015; Roudier et al., 2016) <sup>[[#fn:r491|491]]</sup> .
| Climate services are seeing wide application in sectors such as agriculture, health, disaster management and insurance (Lourenço et al., 2016; Vaughan et al., 2018) <sup>[[#fn:r492|492]]</sup> , with implications for adaptation decision-making (Singh et al., 2017) <sup>[[#fn:r493|493]]</sup> .
|}
<!-- END TABLE -->

<div id="section-4-3-5-7-block-3" class="box"></div>

<span id="cross-chapter-box-9-risks-adaptation-interventions-and-implications-for-sustainable-development-and-equity-across-four-social-ecological-systems-arctic-caribbean-amazon-and-urban"></span>