Editing IPCC:AR6/WGIII/TS (section)

=== TS.5.2 Urban Systems and Other Settlements ===

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'''Although urbanisation is a global trend often associated with increased incomes and higher consumption, the growing concentration of people and activities is an opportunity to increase resource efficiency and decarbonise at scale (''' '''''very high confidence''''' ''').''' The same urbanisation level can have large variations in per-capita urban carbon emissions. For most regions, per-capita urban emissions are lower than per-capita national emissions (excluding aviation, shipping and biogenic sources) ( ''very high confidence'' ). {8.1.4, 8.3.3, 8.4, Box 8.1}

'''Most future urban population growth will occur in developing countries, where per-capita emissions are currently low, but are expected to increase with the construction and use of new infrastructure, and the built environment, and changes in incomes and lifestyles (''' '''''very high confidence''''' ''').''' The drivers of urban GHG emissions are complex and include an interplay of population size, income, state of urbanisation, and how cities are laid out (i.e., urban form). How new cities and towns are designed, constructed, managed, and powered will lock-in behaviour, lifestyles, and future urban GHG emissions. Urban strategies can improve well-being while minimising impact on GHG emissions. However, urbanisation can result in increased global GHG emissions through emissions outside the city’s boundaries ( ''very high confidence'' ) ''.'' {8.1.4, 8.3, Box 8.1, 8.4, 8.6}

'''The urban share of combined global CO''' 2 '''and CH''' ''4'' ''') emissions is substantial and continues to increase (''' '''''high confidence''''' ''').''' In 2015, urban emissions were estimated to be 25GtCO 2 -eq (about 62% of the global share) and in 2020 were 29 GtCO 2 -eq (67–72% of the global share). [[#footnote-012|21]] Around 100 of the highest-emitting urban areas account for approximately 18% of the global carbon footprint ( ''high confidence'' ) ''.'' {8.1, 8.3}

'''The urban share of regional GHG emissions increased between 2000 and 2015, with much inter-regional variation in the magnitude of the increase (''' '''''high confidence''''' ''').''' Globally, the urban share of national emissions increased six percentage points, from 56% in 2000 to 62% in 2015. For 2000 to 2015, the urban emissions share increased from 28% to 38% in Africa, from 46% to 54% in Asia and Pacific, from 62% to 72% in Developed Countries, from 57% to 62% in Eastern Europe and West Central Asia, from 55% to 66% in Latin America and Caribbean, and from 68% to 69% in the Middle East ( ''high confidence'' ) ''.'' {8.1.6, 8.3.3}

'''Per-capita urban GHG emissions increased between 2000 and 2015, with cities in developed countries accounting for nearly seven times more per capita than the lowest emitting region (''' '''''medium confidence''''' ''').''' From 2000 to 2015, global urban GHG emissions per capita increased from 5.5 to 6.2 tCO ''2'' -eq per person (an increase of 11.8%). Emissions in Africa increased from 1.3 to 1.5 tCO ''2'' -eq per person (22.6%); in Asia and Pacific from 3.0 to 5.1 tCO ''2'' -eq per person (71.7%); in Eastern Europe and West Central Asia from 6.9 to 9.8 tCO ''2'' -eq per person (40.9%); in Latin America and the Caribbean from 2.7 to 3.7 tCO ''2'' -eq per person (40.4%); and in the Middle East from 7.4 to 9.6 tCO ''2'' -eq per person (30.1%). Albeit starting from the highest level, developed countries showed a modest decline of 11.4 to 10.7 tCO ''2'' -eq per person (–6.5%). (Figure TS.12) {8.3.3}

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'''Figure TS.12''' '''|''' '''Changes in six metrics associated with urban and national-scale combined CO''' 2 '''and CH''' 4 '''emissions represented in the AR6 WGIII six-region aggregation, with (a) 2000 and (b) 2015.''' The trends in Luqman et al. (2021) were combined with the work of Moran et al. (2018) to estimate the regional urban CO 2 -eq share of global urban emissions, the urban share of national CO 2 -eq emissions, and the urban per capita CO 2 -eq emissions by region. This estimate is derived from consumption-based accounting that includes both direct emissions from within urban areas and indirect emissions from outside urban areas related to the production of electricity, goods, and services consumed in cities. It incorporates all CO 2 and CH 4 emissions except aviation, shipping and biogenic sources (i.e., land-use change, forestry, and agriculture). The dashed grey line represents the global average urban per capita CO 2 -eq emissions. The regional urban population share, regional CO 2 -eq share in total emissions, and national per capita CO 2 -eq emissions by region are given for comparison. Source: adapted from Gurney et al. (2022).

'''The global share of future urban GHG emissions is expected to increase through 2050 with moderate to low mitigation efforts due to growth trends in population, urban land expansion, and infrastructure and service demands, but the extent of the increase depends on the scenario and the scale and timing of urban mitigation action (''' '''''medium confidence''''' ''').''' [[#footnote-011|22]] In modelled scenarios, global consumption-based urban CO 2 and CH 4 emissions are projected to rise from 29 GtCO 2 -eq in 2020 to 34 GtCO 2 -eq in 2050 with moderate mitigation efforts (intermediate GHG emissions, SSP2-4.5), and up to 40 GtCO 2 -eq in 2050 with low mitigation efforts (high GHG emissions, SSP 3-7.0). With aggressive and immediate mitigation efforts to limit global warming to 1.5°C (&gt;50%) with no or limited overshoot by the end of the century (very low emissions, SSP1-1.9), including high levels of electrification, energy and material efficiency, renewable energy preferences, and socio-behavioural responses, urban GHG emissions could approach net-zero and reach a maximum of 3 GtCO 2 -eq in 2050. Under a scenario with aggressive but not immediate urban mitigation policies to limit global warming to 2°C (&gt;67%) (low emissions, SSP1-2.6), urban emissions could reach 17 GtCO 2 -eq in 2050. [[#footnote-010|23]] (Figure TS.13) {8.3.4}

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'''Figure''' '''TS.13 | Panel (a): carbon dioxide-equivalent emissions from global urban areas from 1990 to 2100. Urban areas are aggregated to six regional domains;''' '''Panel (b): comparison of urban emissions under different urbanisation scenarios (GtCO''' 2 '''-eq yr''' –1 ''') for different regions.''' 21 {Figures 8.13 and 8.14}

'''Urban land areas could triple between 2015 and 2050, with significant implications for future carbon lock-in (''' '''''medium confidence''''' ''').''' There is a large range in the forecasts of urban land expansion across scenarios and models, which highlights an opportunity to shape future urban development towards low- or net zero GHG emissions. By 2050, urban areas could increase up to 211% over the 2015 global urban extent, with the median projected increase ranging from 43% to 106%. While the largest absolute amount of new urban land is forecasted to occur in Asia and Pacific, and in Developed Countries, the highest rate of urban land growth is projected to occur in Africa, Eastern Europe and West Central Asia, and in the Middle East. Given past trends, the expansion of urban areas is expected to take place on agricultural lands and forests, with implications for the loss of carbon stocks. The infrastructure that will be constructed concomitant with urban land expansion will lock-in patterns of energy consumption that will persist for decades. {8.3.1, 8.3.4, 8.4.1, 8.6}

'''The construction of new, and upgrading of existing, urban infrastructure through 2030 will add to emissions (''' '''''medium evidence, high agreement''''' ''').''' The construction of new and upgrading of existing urban infrastructure using conventional practices and technologies can result in a significant increase in CO 2 emissions, ranging from 8.5 GtCO 2 to 14 GtCO 2 annually up to 2030 and more than double annual resource requirements for raw materials to about 90 billion tonnes per year by 2050, up from 40 billion tonnes in 2010. {8.4.1, 8.6}

'''Given the dual challenges of rising urban GHG emissions and future projections of more frequent extreme climate events, there is an urgent need to integrate urban mitigation and adaptation strategies for cities to address climate change (''' '''''very high confidence''''' ''').''' Mitigation strategies can enhance resilience against climate change impacts while contributing to social equity, public health, and human well-being. Urban mitigation actions that facilitate economic decoupling can have positive impacts on employment and local economic competitiveness. {8.2, Cross-Working Group Box 2 in Chapter 8, 8.4}

'''Cities can achieve net-zero GHG emissions only through deep decarbonisation and systemic transformation (''' '''''very high confidence''''' ''').''' Three broad mitigation strategies have been found to be effective in reducing emissions when implemented concurrently: (i) reducing or changing urban energy and material use towards more sustainable production and consumption across all sectors, including through compact and efficient urban forms and supporting infrastructure; (ii) electrification and switching to low-carbon energy sources; and (iii) enhancing carbon uptake and storage in the urban environment ( ''high confidence'' ). Given the regional and global reach of urban supply chains, cities can achieve net-zero emissions only if emissions are reduced both within and outside of their administrative boundaries through supply chains. {8.1.6, 8.3.4, 8.4, 8.6}

'''Packages of mitigation policies that implement multiple urban-scale interventions can have cascading effects across sectors, reduce GHG emissions outside a city’s administrative boundaries, and reduce emissions more than the net sum of individual interventions, particularly if multiple scales of governance are included (''' '''''high confidence''''' ''').''' Cities have the ability to implement policy packages across sectors using an urban systems approach, especially those that affect key infrastructure based on spatial planning, electrification of the urban energy system, and urban green and blue infrastructure. The institutional capacity of cities to develop, coordinate, and integrate sectoral mitigation strategies within their jurisdiction varies by context, particularly those related to governance, the regulatory system, and budgetary control. {8.4, 8.5, 8.6}

'''Integrated spatial planning to achieve compact and resource-efficient urban growth through co-location of higher residential and job densities, mixed land use, and transit-oriented development could reduce urban energy use between 23% and 26% by 2050 compared to the business-as-usual scenario (''' '''''high confidence''''' ''').''' Compact cities with shortened distances between housing and jobs, and interventions that support a modal shift away from private motor vehicles towards walking, cycling, and low-emissions shared, or public, transportation, passive energy comfort in buildings, and urban green infrastructure can deliver significant public health benefits and lower GHG emissions. {8.2, 8.3.4, 8.4, 8.6}

'''Urban green and blue infrastructure can mitigate climate change through carbon sinks, avoided emissions, and reduced energy use while offering multiple co-benefits (''' '''''high confidence''''' ''').''' Urban green and blue infrastructure, including urban forests and street trees, permeable surfaces, and green roofs [[#footnote-009|24]] offer potentials to mitigate climate change directly through storing carbon, and indirectly by inducing a cooling effect that both reduces energy demand and reduces energy use for water treatment. Globally, urban trees store approximately 7.4 billion tonnes of carbon, and sequester approximately 217 million tonnes of carbon annually, although carbon storage is highly dependent on biome. Among the multiple co-benefits of green and blue infrastructure are reducing the urban heat island (UHI) effect and heat stress, reducing stormwater runoff, improving air quality, and improving the mental and physical health of urban dwellers. Many of these options also provide benefits to climate adaptation. ( ''high agreement, robust evidence'' ) {8.2, 8.4.4}

'''The potential and sequencing of mitigation strategies to reduce GHG emissions will vary depending on a city’s land use, spatial form, development level, and state of urbanisation (i.e., whether it is an established city with existing infrastructure, a rapidly growing city with new infrastructure, or an emerging city with infrastructure buildup) (''' '''''high confidence''''' ''').''' New and emerging cities will have significant infrastructure development needs to achieve high quality of life, which can be met through energy-efficient infrastructures and services, and people-centred urban design (high confidence). The long lifespan of urban infrastructures locks in behaviour and committed emissions. Urban infrastructures and urban form can enable sociocultural and lifestyle changes that can significantly reduce carbon footprints. Rapidly growing cities can avoid higher future emissions through urban planning to co-locate jobs and housing to achieve compact urban form, and by leapfrogging to low-carbon technologies. Established cities will achieve the largest GHG emissions savings by replacing, repurposing, or retrofitting the building stock, targeted infilling and densifying, as well as through modal shift and the electrification of the urban energy system. New and emerging cities have unparalleled potential to become low or net zero GHG emissions while achieving high quality of life by creating compact, co-located, and walkable urban areas with mixed land use and transit-oriented design, that also preserve existing green and blue assets. {8.2, 8.4, 8.6}

'''With over 880 million people living in informal settlements, there are opportunities to harness and enable informal practices and institutions in cities related to housing, waste, energy, water, and sanitation to reduce resource use and mitigate climate change (''' '''''low evidence, medium agreement''''' ''').''' The upgrading of informal settlements and inadequate housing to improve resilience and well-being offers a chance to create a low-carbon transition. However, there is limited quantifiable data on these practices and their cumulative impacts on GHG emissions. {8.1.4, 8.2.2, Cross-Working Group Box 2 in Chapter 8, 8.3.2, 8.4, 8.6, 8.7}

'''Achieving transformational changes in cities for climate change mitigation and adaptation will require engaging multiple scales of governance, including governments and non-state actors, and in connection with substantial financing beyond sectoral approaches (''' '''''very high confidence''''' ''').''' Large and complex infrastructure projects for urban mitigation are often beyond the capacity of local municipality budgets, jurisdictions, and institutions. Partnerships between cities and international institutions, national and regional governments, transnational networks, and local stakeholders play a pivotal role in mobilising global climate finance resources for a range of infrastructure projects with low-carbon emissions and related spatial planning programs across key sectors. {8.4, 8.5}

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