Editing IPCC:AR6/WGIII/Chapter-8 (section)

== 8.6 A Roadmap for Integrating Mitigation Strategies for Different Urbanisation Typologies ==

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The most effective and appropriate packages of mitigation strategies will vary depending on several dimensions of a city. This section brings together the urban mitigation options described in [[#8.4|Section 8.4]] and assesses the range of mitigation potentials for different types of cities. There is consensus in the literature that mitigation strategies are most effective when multiple interventions are coupled together. Urban-scale interventions that implement multiple strategies concurrently through policy packages are more effective and have greater emissions savings than when single interventions are implemented separately. This is because a city-wide strategy can have cascading effects across sectors, that have multiplicative effects on GHG emissions reduction within and outside a city’s administrative boundaries. Therefore, city-scale strategies can reduce more emissions than the net sum of individual interventions, particularly if multiple scales of governance are included (Sections 8.4 and 8.5). Furthermore, cities have the ability to implement policy packages across sectors using an urban systems approach, such as through planning, particularly those that affect key infrastructures (Figures 8.15, 8.17 and 8.22).

The way that cities are laid out and built will shape the entry points for realising systemic transformation across urban form and infrastructure, energy systems, and supply chains. [[#8.3.1|Section 8.3.1]] discusses the ongoing trend of rapid urbanisation – and how it varies through different forms of urban development or ‘typologies’ (Figure 8.6). Below, Figure 8.20 distils the typologies of urban growth across three categories: emerging, rapidly growing, and established. Urban growth is relatively stabilised in established urban areas with mature urban form while newly taking shape in emerging urban areas. In contrast, rapidly growing urban areas experience pronounced changes in outward and/or upward growth. These typologies are not mutually exclusive, and can co-exist within an urban system; cities typically encompass a spectrum of development, with multiple types of urban form and various typologies ( [[#Mahtta--2019|Mahtta et al. 2019]] ).

Taken together, urban form (Figure 8.16) and growth typology (Figure 8.20) can act as a roadmap for cities or sub-city communities looking to identify their urban context and, by extension, the mitigation opportunities with the greatest potential to reduce GHG emissions. Specifically, this considers whether a city is established with existing and managed infrastructure; rapidly growing with new and actively developing infrastructure; or emerging with large amounts of infrastructure build-up. The long lifespan of urban infrastructure locks in behaviour and committed emissions. Therefore, the sequencing of mitigation strategies is important for determining emissions savings in the short and long term. Hence, different types of cities will have different mitigation pathways, depending upon a city’s urban form and state of that city’s urban development and infrastructure; the policy packages and implementation plan that provide the highest mitigation potential for rapidly growing cities with new infrastructures will differ from those for established cities with existing infrastructure.

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'''Figure 8.20: Urban growth typologies define the main patterns of urban development.''' Emerging urban areas are undergoing the buildup of new infrastructure. These are new urban areas that are budding out. Rapidly growing urban areas are undergoing significant changes in either outward and/or upward growth, accompanied by large-scale development of new urban infrastructure. Established urban areas are relatively stable with mature urban form and existing urban infrastructures. Each of these typologies represents different levels of economic development and state of urbanisation. Rapidly growing urban areas that are building up through vertical development are often those with higher levels of economic development. Rapidly growing urban areas that are building outward through horizontal expansion are found at lower levels of economic development and are land intensive. Like with urban form, different areas of a single city can undergo different growth typologies. Therefore a city will be comprised of multiple urban growth typologies. Source: synthesized from [[#Mahtta--2019|Mahtta et al. (2019)]] and [[#Lall--2021|Lall et al. (2021)]] .

Mitigation options that involve spatial planning, urban form, and infrastructure – particularly co-located and mixed land use, as well as TOD – provide the greatest opportunities when urban areas are rapidly growing or emerging ( [[#8.4.2|Section 8.4.2]] ). Established urban areas that are already compact and walkable have captured mitigation benefits from these illustrative strategies to various extents. Conversely, established urban areas that are dispersed and auto-centric have foregone these opportunities, with the exception of urban infill and densification that can be used to transform or continue to transform the existing urban form. Figure 8.21 underscores that urban mitigation options and illustrative strategies differ by urban growth typologies and urban form. Cities can identify their entry points for sequencing mitigation strategies.

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'''Figure 8.21: Priorities and potentials for packages of urban mitigation strategies across typologies of urban growth (Figure''' '''8.''' '''20) and urban form (Figure 8.16).''' The horizontal axis represents urban growth typologies based on emerging, rapidly growing, and established urban areas. The vertical axis shows the continuum of urban form, from compact and walkable, to dispersed and auto-centric. Urban areas can first locate their relative positioning in this space according to their predominant style of urban growth and urban form. The urban mitigation options are bundled across four broad sectors of mitigation strategies: (i) spatial planning, urban form, and infrastructure (blue); (ii) electrification and net-zero-emissions resources (yellow); (iii) urban green and blue infrastructure (green); and (iv) socio-behavioural aspects (purple). The concentric circles indicate lower, medium, and higher mitigation potential considering the context of the urban area. For each city type (circular graphic) the illustrative urban mitigation strategy that is considered to provide the greatest cascading effects across mitigation opportunities is represented by a section that is larger relative to others; those strategy sections outlined in black are ‘entry points’ for sequencing of strategies. Within each of the larger strategy sections (i.e., spatial planning, urban green and blue infrastructure, etc.), the size of the sub-strategy sections are equal and do not suggest any priority or sequencing. The relative sizes of the strategies and extent of mitigation potential are illustrative and based on the authors’ best understanding and assessment of the literature.

The emissions reduction potential of urban mitigation options further varies based on governance contexts, institutional capacity, and economic structure, as well as human and physical geography. According to the development level, for instance, urban form can remain mostly planned or unplanned, taking place spontaneously, with persistent urban infrastructure gaps remaining ( [[#Lwasa--2018|Lwasa et al. 2018]] ; [[#Kareem--2020|Kareem et al. 2020]] ). Measures for closing the urban infrastructure gap while addressing ‘leapfrogging’ opportunities (see Glossary) for mitigation and providing co-benefits represent possibilities for shifting development paths for sustainability (Cross-Chapter Box 5 in Chapter 4).

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=== 8.6.1 Mitigation Opportunities for Est ablished Cities ===

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'''Established cities will achieve the largest GHG emissions savings by replacing, repurposing, or retrofitting the building stock, encouraging modal shift, electrifying the urban energy system, as well as infilling and densifyi''' '''ng urban areas.'''

Shifting pathways to low-carbon development for established cities with existing infrastructures and locked-in behaviours and lifestyles is admittedly challenging. Urban infrastructures such as buildings, roads, and pipelines often have long lifetimes that lock-in emissions, as well as institutional and individual behaviour. Although the expected lifetime of buildings varies considerably by geography, design, and materials, typical lifespans are at minimum 30 years to more than 100 years.

Cities where urban infrastructure has already been built have opportunities to increase energy efficiency measures, prioritise compact and mixed-use neighbourhoods through urban regeneration, advance the urban energy system through electrification, undertake cross-sector synergies, integrate urban green and blue infrastructure, encourage behavioural and lifestyle change to reinforce climate mitigation, and put into place a wide range of enabling conditions as necessary to guide and coordinate actions in the urban system and its impacts in the global system. Retrofitting buildings with state of the art deep-energy retrofit measures could reduce emissions of the existing stock by about 30–60% ( [[#Creutzig--2016a|Creutzig et al. 2016a]] ) and in some cases up to 80% ( [[#Ürge-Vorsatz--2020|Ürge-Vorsatz et al. 2020]] ) ( [[#8.4.3|Section 8.4.3]] ).

Established cities that are compact and walkable are likely to have low per capita emissions, and thus can keep emissions low by focusing on electrification of all urban energy services and using urban green and blue infrastructure to sequester and store carbon while reducing urban heat stress. Illustrative mitigation strategies with the highest mitigation potential are decarbonising electricity and energy carriers while electrifying mobility, heating, and cooling (Table 8.3 and Figure 8.19). Within integrated strategies, the importance of urban forests, street trees, and green space as well as green roofs, walls, and retrofits, also have high mitigation potential ( [[#8.4.4|Section 8.4.4]] and Figure 8.18).

'''Table 8.3: Cross-cutting implications of the reference scenarios and Illustrative Mitigation Pathways (IMPs) for urban areas.''' The IMPs illustrate key themes of mitigation strategies throughout the WGIII report ( [[IPCC:Wg3:Chapter:Chapter-3#3.2.5|Section 3.2.5]] ). The implications of the key themes of the six IMPs (in addition to two pathways illustrative of higher emissions) for mitigation in urban areas are represented based on the main storyline elements that involve energy, land use, food biodiversity and lifestyle, as well as policy and innovation. The cross-cutting implications of these elements for urban areas, where multiple elements interact, are summarised for each reference scenario and the IMPs. IMP-Ren, IMP-LD and IMP-SP represent pathways in the C1 category that also includes SSP1–1.9. Source: adapted from the key themes of the IMPs for urban areas.

{| class="wikitable"
|-
! '''Reference scenarios and IMPs'''

! '''Cross-cutting implications for urban areas'''

|-
| '''Current Policies (CurPol scenario)'''

| – Urban mitigation is challenged by overcoming lock-in to fossil fuel consumption; also with car-based and low-density urban growth prevailing

– Consumption patterns have land impacts, supply chains remain the same, urban inhabitants have limited participation in mitigation options

– Progress in low-carbon urban development takes place at a relatively slower pace and there is limited policy learning within climate networks

|-
| '''Moderate Action (ModAct scenarios)'''

| – Renewable energy continues to increase its share that is supported by urban areas to a more limited extent with ongoing lock-in effects

– Changes in land use, consumption patterns, and lifestyles mostly continue as before with negligible changes taking place – if any

– The fragmented policy landscape also prevails at the urban level with different levels of ambitions and without integration across the urban system

|-
| '''Gradual Strengthening (IMP-GS)'''

| – Urban areas depend upon energy supply from distant power plants or those in rural areas without rapid progress in urban electrification

– Afforestation/reforestation is supported with some delay while lower incentives for limiting growth in urban extent provide inconsistencies

– The mobilisation of urban actors for GHG emission reductions is strengthened more gradually with stronger coordination taking place after 2030

|-
| '''Net Negative Emissions (IMP-Neg)'''

| – Urban areas depend upon energy supply from distant power plants or those in rural areas with more limited electrification in urban energy systems

– Afforestation/reforestation is supported to a certain extent while lower incentives for limiting growth in urban extent provide inconsistencies

– Urban areas are less prominent in policy and innovation given emphasis on carbon capture and storage (CCS) options. Rural areas are more prominent considering BECCS

|-
| '''Renewable Energy (IMP-Ren)'''

| – Urban areas support renewable energy penetration with electrification of urban infrastructure and sector coupling for increasing system flexibility

– Consumption patterns and urban planning are able to reduce pressures on land use, demand response is increased to support renewables

– Urban climate governance is enabling rapid deployment of renewable energy while fostering innovation for sustainable urban planning

|-
| '''Low Demand (IMP-LD)'''

| – Walkable urban form is increased, active and public transport modes are encouraged, low-energy buildings and green-blue infrastructure is integrated

– Changes in consumption patterns and urban planning reduce pressures on land use to lower levels while service provisioning is improved

– Urban policymaking is used to accelerate solutions that foster innovation and increased efficiencies across all sectors, including material use

|-
| '''Shifting Pathways (IMP-SP)'''

| – Urban areas are transformed to be resource efficient, low demand, and renewable energy supportive with an integrated approach in urban planning

– Reinforcing measures enable GHG emission reductions from consumption patterns while also avoiding resource impacts across systems

– Urban climate mitigation is best aligned with the SDGs to accelerate GHG emission reductions, increasing both scalability and acceptance

|}

Established cities that are dispersed and auto-centric are likely to have higher per capita emissions and thus can reduce emissions by focusing on creating modal shift and improving public transit systems in order to reduce urban transport emissions, as well as focusing on infilling and densifying. Only then can the urban form constraints on locational and mobility options be effective at reducing transport-based emissions. Among mitigation options based on spatial planning, urban form, and infrastructure, urban infill and densification has priority. For these cities, the use of urban green and blue infrastructure will be essential to offset residual emissions that cannot be reduced because their urban form is already established and difficult to change.

System-wide energy savings and emissions reductions for low-carbon urban development are widely recognised to require both behavioural and structural changes ( [[#Zhang--2017|Zhang and Li 2017]] ). Synergies between social and ecological innovation can reinforce the sustainability of urban systems while decoupling energy usage and economic growth ( [[#Hu--2018|Hu et al. 2018]] ; [[#Ma--2018|Ma et al. 2018]] ). In addition, an integrated sustainable development approach that enables cross-sector energy efficiency, sustainable transport, renewable energy, and local development in urban neighbourhoods can address issues of energy poverty ( [[#Pukšec--2018|Pukšec et al. 2018]] ). In this context, cross-sectoral, multi-scale, and public-private collaborative action is crucial to steer societies and cities closer to low-carbon futures ( [[#Hölscher--2019|Hölscher et al. 2019]] ). Such actions include guiding residential living area per capita, limiting private vehicle growth, expanding public transport, improving the efficiency of urban infrastructure, enhancing urban carbon pools, and minimising waste through sustainable, ideally circular, waste management ( [[#Lin--2018|Lin et al. 2018]] ). Through a coordinated approach, urban areas can be transformed into hubs for renewable and distributed energy, sustainable mobility, as well as inclusivity and health ( [[#Newman--2017|Newman et al. 2017]] ; [[#Newman--2020|]] [[#Newman--2020|Newman 2020]] ).

Urban design for existing urban areas includes strategies for urban energy transitions for carbon neutrality based on renewable energy, district heating for the city centre and suburbs, as well as green and blue interfaces ( [[#Pulselli--2021|Pulselli et al. 2021]] ). Integrated modelling approaches for urban energy system planning, including land use and transport and flexible demand-side options, is increased when municipal actors are also recognised as energy planners ( [[#Yazdanie--2021|Yazdanie and Orehounig 2021]] ) ( [[#8.4.3|Section 8.4.3]] ). Enablers for action can include the co-design of infill residential development through an inclusive and participatory process with citizen utilities and disruptive innovation that can support net-zero-carbon power while contributing to 1.5°C pathways, the SDGs, and affordable housing simultaneously ( [[#Wiktorowicz--2018|Wiktorowicz et al. 2018]] ). Cross-sectoral strategies for established cities, including those taking place among 120 urban areas, also involve opportunities for sustainable development ( [[#Kılkış--2019|Kılkış 2019]] , 2021b).

A shared understanding for urban transformation through a participatory approach can largely avoid maladaptation and contribute to equity ( [[#Moglia--2018|Moglia et al. 2018]] ). Transformative urban futures that are radically different from the existing trajectories of urbanisation, including in developing countries, can remain within planetary boundaries while being inclusive of the urban poor ( [[#Friend--2016|Friend et al. 2016]] ). At the urban policy level, an analysis of 12,000 measures in urban-level monitoring emissions inventories based on the mode of governance further suggests that local authorities with lower population have primarily relied on municipal self-governing while local authorities with higher population more frequently adopted regulatory measures as well as financing and provision ( [[#Palermo--2020b|Palermo et al. 2020b]] ). Policies that relate to education and enabling were uniformly adopted regardless of population size ( [[#Palermo--2020b|Palermo et al. 2020b]] ). Multi-disciplinary teams, including urban planners, engineers, architects, and environmental institutions, can support local decision-making capacities, including for increasing energy efficiency and renewable energy considering building intensity and energy use ( [[#Mrówczyńska--2021|Mrówczyńska et al. 2021]] ) ( [[#8.5|Section 8.5]] ).

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=== 8.6.2 Mitigation Opportunities for Rapidly Growing Cities ===

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'''Rapidly growing cities with new and actively developing infrastructures can avoid higher future emissions through using urban planning to co-locate jobs and housing, and achieve compact urban form; leapfrogging to low-carbon technologies; electrifying all urban services, including transportation, cooling, heating, cooking, recycling, water extraction, wastewater recycling, and so on; and preserving and managing existing green a''' '''nd blue assets.'''

Rapidly growing cities have significant opportunities for integrating climate mitigation response options in earlier stages of urban development, which can provide even greater opportunities for avoiding carbon lock-in and shifting pathways towards net-zero GHG emissions. In growing cities that are expected to experience large increases in population, a significant share of urban development remains to be planned and built. The ability to shift these investments towards low-carbon development earlier in the process represents an important opportunity for contributing to net-zero GHG emissions at the global scale. In particular, evidence suggests that investment in low-carbon development measures and reinvestment based on the returns of the measures, even without considering substantial co-benefits, can provide tipping points for climate mitigation action and reaching peak emissions at lower levels while decoupling emissions from economic growth, even in fast-growing megacity contexts with well-established infrastructure ( [[#Colenbrander--2017|Colenbrander et al. 2017]] ).

At the same time, some of the rapidly growing cities in developing countries can have existing walkable urban design that can be maintained and supported with electrified urban rail plus renewable-energy-based solutions to avoid a shift to private vehicles ( [[#Sharma--2018|Sharma 2018]] ). In addition, community-based distributed renewable electricity can be applicable for the regeneration of informal settlements rather than more expensive informal settlement clearance ( [[#Teferi--2018|Teferi and Newman 2018]] ). Scalable options for decentralised energy, water, and wastewater systems, as well as spatial planning and urban agriculture and forestry, are applicable to urban settlements across multiple regions simultaneously ( [[#Lwasa--2017|Lwasa 2017]] ).

Rapidly urbanising areas can experience pressure for rapid growth in urban infrastructure to address growth in population. This challenge can be addressed with coordinated urban planning and support from enabling conditions for pursuing effective climate mitigation ( [[#8.5|Section 8.5]] and Box 8.3). The ability to mobilise low-carbon development will also increase opportunities for capturing co-benefits for urban inhabitants while reducing embodied and operational emissions. Transforming urban growth, including its impacts on energy and materials, can be carefully addressed with the integration of cross-sectoral strategies and policies.

Rapidly growing cities have entry points into an integrated strategy based on spatial planning, urban form and infrastructure (Figure 8.21). For rapidly growing cities that may be co-located and walkable at present, remaining compact is better ensured when co-location and mixed land use, as well as TOD, continues to be prioritised ( [[#8.4.2|Section 8.4.2]] ). Concurrently, ensuring that electricity and energy carriers are decarbonised while electrifying mobility, heating and cooling will support the mitigation potential of these cities. Along with an integrated approach across other illustrative strategies, switching to net-zero materials and supply chains holds importance ( [[#8.4.3|Section 8.4.3]] ). Cities that remain compact and walkable can provide a greater array of locational and mobility options to the inhabitants that can be adopted for mitigation benefits. Rapidly growing cities that may currently be dispersed and auto-centric can capture high mitigation potential through urban infill and densification. Conserving existing green and blue assets, thereby protecting sources of carbon storage and sequestration, as well as biodiversity, have high potential for both kinds of existing urban form, especially when the rapid growth can be controlled.

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=== 8.6.3 Mitigation Opportunities for New and E merging Cities ===

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'''New and emerging cities have unparalleled potential to become low- or net-zero-emissions urban areas while achieving high quality of life by creating compact, co-located, and walkable urban areas with mixed land use and TOD, that also preserve existing green a''' '''nd blue assets.'''

The fundamental building blocks that make up the physical attributes of cities, such as the layout of streets, the size of the city blocks, the location of where people live versus where they work, can affect and lock in energy demand for long time periods ( [[#Seto--2016|Seto et al. 2016]] ) ( [[#8.4.1|Section 8.4.1]] ). A large share of urban infrastructures that will be in place by 2050 has yet to be constructed and their design and implementation will determine both future GHG emissions as well as the ability to meet mitigation goals ( [[#Creutzig--2016a|Creutzig et al. 2016a]] ) (Figure 8.10 and Table 8.1). Thus, there are tremendous opportunities for new and emerging cities to be designed and constructed to be low-emissions while providing high quality of life for their populations.

The UN International Resource Panel (IRP) estimates that building future cities under conventional practices will require a more than doubling of material consumption, from 40 billion tonnes annually in 2010 to about 90 billion tonnes annually by 2050 ( [[#Swilling--2018|Swilling et al. 2018]] ). Thus, the demand that new and emerging cities will place on natural resource use, materials, and emissions can be minimised and avoided only if urban settlements are planned and built much differently than today, including minimised impacts on land use based on compact urban form, lowered use of materials, and related cross-sector integration, including energy-driven urban design for sustainable urbanisation.

Minimising and avoiding raw material demands depends on alternative options while accommodating the urban population. In addition, operational emissions that can be committed by new urban infrastructure can range between 8.5 GtCO 2 and 14 GtCO 2 annually up to 2030 ( [[#Erickson--2015|Erickson and Tempest 2015]] ). Buildings and road networks are strongly influenced by urban layouts, densities, and specific uses. Cities that are planned and built much differently than today through light-weighting, material substitution, resource efficiency, renewable energy, and compact urban form, have the potential to support more sustainable urbanisation and provide co-benefits for inhabitants (Figures 8.17 and 8.22).

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'''Figure 8.22: Raw material demands and committed emissions from building urban areas.''' The horizontal bars represent the projected increase in raw material demands in the year 2050. The vertical bars represent the possible range of committed CO 2 emissions in 2030. The importance of alternative solutions to reduce raw material demands and committed emissions while increasing co-benefits is represented by the circular process on the right-hand side. Ranges for committed emissions from new urban infrastructure are based on [[#Erickson--2015|Erickson and Tempest (2015)]] SEI WP 11. Source: drawn using data from [[#Erickson--2015|Erickson and Tempest (2015)]] and [[#Swilling--2018|Swilling et al. (2018)]] .

In this context, illustrative mitigation strategies that can serve as a roadmap for emerging cities includes priorities for co-located and mixed land use, as well as TOD, within an integrated approach (Table 8.3 and Figure 8.19). This has cascading effects, including conserving existing green and blue assets (e.g., forests, grasslands, wetlands), many of which sequester and store carbon. Priorities for decarbonising electricity and energy carriers while electrifying mobility, heating, and cooling take place within the integrated approach ( [[#8.4.3|Section 8.4.3]] ). Increasing greenways and permeable surfaces, especially from the design of emerging urban areas onward, can be pursued, also for adaptation co-benefits and linkages with the SDGs ( [[#8.4.4|Section 8.4.4]] and Figure 8.18).

In low-energy-driven urban design, parameters are evaluated based on the energy performance of the urban area in the early design phase of future urban development ( [[#Shi--2017b|Shi et al. 2017b]] ). Energy-driven urban design generates and optimises urban form according to the energy performance outcome ( [[#Shi--2017b|Shi et al. 2017b]] ). Beyond the impact of urban form on building energy performance, the approach focuses on the interdependencies between urban form and energy infrastructure in urban energy systems. The process can provide opportunities for both passive options for energy-driven urban design, such as the use of solar gain for space heating, or of thermal mass to moderate indoor temperatures, as well as active options that involve the use of energy infrastructure and technologies while recognising interrelations of the system. Future urban settlements can also be planned and built with net-zero CO 2 or net-zero GHG emissions, as well as renewable energy targets, in mind. Energy master planning of urban areas that initially target net-zero operational GHG emissions can be supported with energy master planning from conceptual design to operation, including district-scale energy strategies ( [[#Charani%20Shandiz--2021|Charani Shandiz et al. 2021]] ).

Integrated scenarios across sectors at the local level can decouple resource usage from economic growth ( [[#Hu--2018|Hu et al. 2018]] ) and enable 100% renewable energy scenarios ( [[#Zhao--2017a|Zhao et al. 2017a]] ; [[#Bačeković--2018|Bačeković and Østergaard 2018]] ). Relative decoupling is obtained ( [[#Kalmykova--2015|Kalmykova et al. 2015]] ) with increasing evidence for turning points in per capita emissions, total emissions, or urban metabolism ( [[#Chen--2018b|Chen et al. 2018b]] ; [[#Shen--2018|Shen et al. 2018]] ). The importance of integrating energy and resource efficiency in sustainable and low-carbon city planning ( [[#Dienst--2015|Dienst et al. 2015]] ), structural changes, as well as forms of disruptive social innovation, such as the ‘sharing economy’ (see Glossary), is also evident based on analyses for multiple cities, including those that can be used to lower the carbon footprints of urban areas relative to sub-urban areas ( [[#Chen--2018a|Chen et al. 2018a]] ).

To minimise carbon footprints, new cities can utilise new intelligence functions as well as changes in energy sources and material processes. Core design strategies of a compact city can be facilitated by data-driven decision-making so that new urban intelligence functions are holistic and proactive rather than reactive ( [[#Bibri--2020|Bibri 2020]] ). In mainstream practices, for example, many cities use environmental impact reviews to identify potentially negative consequences of individual development projects on environmental conditions on a piecemeal project basis.

New cities can utilise: system-wide analyses of construction materials, or renewable power sources, that minimise ecosystem disruption and energy use, through the use of lifecycle assessments for building types permitted in the new city ( [[#Ingrao--2019|Ingrao et al. 2019]] ); urban-scale metabolic impact assessments for neighbourhoods in the city ( [[#Pinho--2019|Pinho and Fernandes 2019]] ); strategic environmental assessments (SEAs) that go beyond the individual project and assess plans for neighbourhoods ( [[#Noble--2017|Noble and Nwanekezie 2017]] ); or modelling of the type and location of building masses, tree canopies and parks, and temperature (surface conditions) and prevailing winds profiles to reduce the combined effects of climate change and UHI phenomena, thus minimising the need for air conditioning ( [[#Matsuo--2019|Matsuo and Tanaka 2019]] ).

Resource-efficient, compact, sustainable, and liveable urban areas can be enabled with an integrated approach across sectors, strategies, and innovations. From a geophysical perspective, the use of materials with lower lifecycle GHG impacts, including the use of timber in urban infrastructure and the selection of urban development plans with lower material and land demand can lower the emission impacts of existing and future cities ( [[#Müller--2013|Müller et al. 2013]] ; [[#Carpio--2016|Carpio et al. 2016]] ; [[#Liu--2016a|Liu et al. 2016a]] ; [[#Ramage--2017|Ramage et al. 2017]] ; [[#Shi--2017a|Shi et al. 2017a]] ; Stocchero et al. 2017; [[#Bai--2018|Bai et al. 2018]] ; [[#Zhan--2018b|Zhan et al. 2018b]] ; [[#Swilling--2018|Swilling et al. 2018]] ; [[#Xu--2018b|Xu et al. 2018b]] ; [[#UNEP%20IRP--2020|UNEP IRP 2020]] ) (Figure 8.17). The capacity to implement relevant policy instruments in an integrated and coordinated manner within a policy mix while leveraging multi-level support as relevant can increase the enabling conditions for urban system transformation ( [[#Agyepong--2017|Agyepong and Nhamo 2017]] ; [[#Roppongi--2017|Roppongi et al. 2017]] ).

The integration of urban land use and spatial planning, electrification of urban energy systems, renewable energy district heating and cooling networks, urban green and blue infrastructure, and circular economy can also have positive impacts on improving air and environmental quality with related co-benefits for health and well-being ( [[#Diallo--2016|Diallo et al. 2016]] ; [[#Nieuwenhuijsen--2016|Nieuwenhuijsen and Khreis 2016]] ; [[#Shakya--2016|Shakya 2016]] ; [[#Liu--2017|Liu et al. 2017]] ; [[#Ramaswami--2017a|Ramaswami et al. 2017a]] ; [[#Sun--2018b|Sun et al. 2018b]] ; [[#Tayarani--2018|Tayarani et al. 2018]] ; [[#Park--2019|Park and Sener 2019]] ; [[#González-García--2021|González-García et al. 2021]] ). Low-carbon development options can be implemented in ways that reduce impacts on water use, including water use efficiency, demand management, and water recycling, while increasing water quality ( [[#Koop--2015|Koop and van Leeuwen 2015]] ; [[#Topi--2016|Topi et al. 2016]] ; [[#Drangert--2017|Drangert and Sharatchandra 2017]] ; [[#Lam--2017|Lam et al. 2017]] , 2018; [[#Vanham--2017|Vanham et al. 2017]] ; [[#Kim--2018|Kim and Chen 2018]] ). The ability to enhance biodiversity while addressing climate change depends on improving urban metabolism and biophilic urbanism towards urban areas that are able to regenerate natural capital ( [[#Thomson--2018|Thomson and Newman 2018]] ; [[#IPBES--2019b|IPBES 2019b]] ).

There are readily available solutions for low-carbon urban development that can be further supported by new and emerging ones, such as tools for optimising the impact of urban form on energy infrastructure ( [[#Hu--2015|Hu et al. 2015]] ; [[#Shi--2017b|Shi et al. 2017b]] ; [[#Xue--2017|Xue et al. 2017]] ; [[#Dobler--2018|Dobler et al. 2018]] ; [[#Egusquiza--2018|Egusquiza et al. 2018]] ; [[#Pedro--2018|Pedro et al. 2018]] ; [[#Soilán--2018|Soilán et al. 2018]] ). The costs of low-carbon urban development are manageable, and enhanced with a portfolio approach for cost-effective, cost-neutral, and reinvestment options with evidence across different urban typologies ( [[#Colenbrander--2015|Colenbrander et al. 2015]] , 2017; [[#Gouldson--2015|Gouldson et al. 2015]] ; [[#Nieuwenhuijsen--2016|Nieuwenhuijsen and Khreis 2016]] ; [[#Saujot--2016|Saujot and Lefèvre 2016]] ; [[#Sudmant--2016|Sudmant et al. 2016]] ; [[#Brozynski--2018|Brozynski and Leibowicz 2018]] ).

Low-carbon urban development that triggers economic decoupling can have a positive impact on employment and local competitiveness ( [[#Kalmykova--2015|Kalmykova et al. 2015]] ; [[#Chen--2018b|Chen et al. 2018b]] ; [[#García-Gusano--2018|García-Gusano et al. 2018]] ; [[#Hu--2018|Hu et al. 2018]] ; [[#Shen--2018|Shen et al. 2018]] ). In addition, sustainable urban transformation can be supported with participatory approaches that provide a shared understanding of future opportunities and challenges where public acceptance increases with citizen engagement and citizen empowerment as well as an awareness of co-benefits ( [[#Blanchet--2015|Blanchet 2015]] ; [[#Bjørkelund--2016|Bjørkelund et al. 2016]] ; [[#Flacke--2017|Flacke and de Boer 2017]] ; [[#Gao--2017|Gao et al. 2017]] ; [[#Neuvonen--2017|Neuvonen and Ache 2017]] ; [[#Sharp--2017|Sharp and Salter 2017]] ; [[#Wiktorowicz--2018|Wiktorowicz et al. 2018]] ; [[#Fastenrath--2018|Fastenrath and Braun 2018]] ; [[#Gorissen--2018|Gorissen et al. 2018]] ; [[#Herrmann--2018|Herrmann et al. 2018]] ; [[#Moglia--2018|Moglia et al. 2018]] ). Sustainable and low-carbon urban development that integrates issues of equity, inclusivity, and affordability, while safeguarding urban livelihoods, providing access to basic services, lowering energy bills, addressing energy poverty, and improving public health can also improve the distributional effects of existing and future urbanisation ( [[#Friend--2016|Friend et al. 2016]] ; [[#Claude--2017|Claude et al. 2017]] ; [[#Colenbrander--2017|Colenbrander et al. 2017]] ; [[#Ma--2018|Ma et al. 2018]] ; [[#Mrówczyńska--2018|Mrówczyńska et al. 2018]] ; [[#Pukšec--2018|Pukšec et al. 2018]] ; [[#Wiktorowicz--2018|Wiktorowicz et al. 2018]] ) ( [[#8.2|Section 8.2]] ).

Information and communications technologies can play an important role for integrating mitigation options at the urban systems level for achieving zero-carbon cities. Planning for decarbonisation at the urban systems level involves integrated considerations of the interaction among sectors, including synergies and trade-offs among households, businesses, transport, land use, and lifestyles. The utilisation of big data, artificial intelligence and internet of things (IoT) technologies can be used to plan, evaluate and integrate rapidly progressing transport and building technologies, such as autonomous EVs, zero-energy buildings, and districts as an urban system, including energy-driven urban design ( [[#Creutzig--2020|Creutzig et al. 2020]] ; [[#Yamagata--2020|Yamagata et al. 2020]] ). Community-level energy sharing systems will contribute to realising the decarbonisation potential of urban systems at community scale, including in smart cities ( [[IPCC:Wg3:Chapter:Chapter-4#4.2.5.9|Section 4.2.5.9]] , Box 10.1, and Cross-Chapter Box 11 in Chapter 16).

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