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

=== 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"
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! '''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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