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

=== 8.1.1 What Is New Since AR5? ===

<div id="h2-1-siblings" class="h2-siblings"></div>

The Fifth Assessment Report (AR5) of the Intergovernmental Panel on Climate Change (IPCC) was the first IPCC report that had a standalone chapter on urban mitigation of climate change. The starting point for that chapter was how the spatial organisation of urban settlements affects greenhouse gas (GHG) emissions and how urban form and infrastructure could facilitate mitigation of climate change. A main finding in AR5 was that urban form shapes urban energy consumption and GHG emissions.

Since AR5, there has been growing scientific literature and policy foci on urban strategies for climate change mitigation. There are three possible reasons for this. First, according to AR5 Working Group III (WGIII) [[IPCC:Wg3:Chapter:Chapter-12|Chapter 12]] on Human Settlements, Infrastructure, and Spatial Planning, urban areas generate between 71% and 76% of carbon dioxide (CO 2 ) emissions from global final energy use and between 67% and 76% of global energy (Seto et al. 2014). Thus, focusing on ‘urban systems’ (see Annex I: Glossary and Figure 8.15) addresses one of the key drivers of emissions. Second, more than half of the world population lives in urban areas, and by mid-century 7 out of 10 people on the planet will live in a town or a city ( [[#UN%20DESA--2019|UN DESA 2019]] ). Thus, coming up with mitigation strategies that are relevant to urban settlements is critical for successful mitigation of climate change. Third, beyond climate change, there is growing attention on cities as major catalysts of change and to help achieve the objectives outlined in multiple international frameworks and assessments.

<div id="_idContainer006" class="Basic-Text-Frame"></div>

[[File:3ad214b95773938fed8dd3d42a849e8e IPCC_AR6_WGIII_Figure_8_1.png]]

'''Figure 8.1''' 4 ''': Relationship between urbanisation level and gross national income (GNI).''' There is a positive and strong correlation between the urbanisation level and gross national income. High-income countries have high levels of urbanisation, on average 80%. Low-income countries have low levels of urbanisation, on average 30%. Source: [[#UN%20DESA--2019|UN DESA 2019]] , p. 42.

Cities are also gaining traction within the work of the IPCC. The IPCC Special Report on Global Warming of 1.5°C (SR1.5 Chapter 4) identified four systems that urgently need to change in fundamental and transformative ways: urban infrastructure, land use and ecosystems, industry, and energy. Urban infrastructure was singled out but urban systems form a pivotal part of the other three systems requiring change ( [[#IPCC--2018a|IPCC 2018a]] ) (see ‘infrastructure’ in Glossary). The IPCC Special Report on Climate Change and Land (SRCCL) identified cities not only as spatial units for land-based mitigation options but also places for managing demand for natural resources including food, fibre, and water ( [[#IPCC--2019|IPCC 2019]] ).

Other international frameworks are highlighting the importance of cities. For example, the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES) report on nature’s contribution to people is clear: cities straddle the biodiversity sphere in the sense that they present spatial units of ecosystem fragmentation and degradation while at the same time contain spatial units where the concentration of biodiversity compares favourably with some landscapes (IPBES 2019a). Cities are also featured as a key element in the transformational governance to tackle both climate change and biodiversity and ecosystem challenges in the first-ever IPCC-IPBES co-sponsored workshop report ( [[#Pörtner--2021|Pörtner et al. 2021]] ) ( [[#8.5|Section 8.5]] and see ‘governance’ in Glossary).

The UN Sustainable Development Goals (SDGs) further underscore the importance of cities in the international arena with the inclusion of SDG 11 on Sustainable Cities and Communities for ‘inclusive, safe, resilient and sustainable’ cities and human settlements ( [[#United%20Nations--2015|United Nations 2015]] ; [[#Queiroz--2017|Queiroz et al. 2017]] ; [[#United%20Nations--2019|United Nations 2019]] ). Additionally, UN-Habitat’s New Urban Agenda (NUA) calls for various measures, including integrated spatial planning at the city-regional scale, to address the systemic challenges included in greening cities, among which is emissions reduction and avoidance ( [[#United%20Nations--2017|United Nations 2017]] ).

Since AR5, there has also been an increase in scientific literature on urban mitigation of climate change, including more diversity of mitigation strategies than were covered during AR5 ( [[#Lamb--2018|Lamb et al. 2018]] ), as well as a growing focus on how strategies at the urban scale can have compounding or additive effects beyond urban areas (e.g., in rural areas, land-use planning, and the energy sector).

There is more literature on using a systems approach to understand the interlinkages between mitigation and adaptation, and situating GHG emissions reduction targets within broader social, economic, and human well-being contexts and goals ( [[#Bai--2018|Bai et al. 2018]] ; [[#Ürge-Vorsatz--2018|Ürge-Vorsatz et al. 2018]] ; [[#Lin--2021|Lin et al. 2021]] ). In particular, the nexus approach, such as the water and energy nexus and the water-energy-food nexus, is increasingly being used to understand potential emissions and energy savings from cross-sectoral linkages that occur in cities ( [[#Wang--2016|Wang and Chen 2016]] ; [[#Engström--2017|Engström et al. 2017]] ; [[#Valek--2017|Valek et al. 2017]] ). There is also a growing literature that aims to quantify transboundary urban GHG emissions and carbon footprint beyond urban and national administrative boundaries ( [[#Chen--2016|Chen et al. 2016]] ; [[#Hu--2016|Hu et al. 2016]] ). Such a scope provides a more complete understanding of how local urban emissions or local mitigation strategies can have effects on regions’ carbon footprint or GHG emissions.

<div id="8.1.1.1" class="h3-container"></div>

<span id="city-climate-action"></span>
==== 8.1.1.1 City Climate Action ====

<div id="h3-1-siblings" class="h3-siblings"></div>

Moreover, cities around the world are putting increasing focus on tackling climate change. Since AR5:

• Climate leadership at the local scale is growing with commitment from city decision-makers and policymakers to implement local-scale mitigation strategies ( [[#GCoM--2018|GCoM 2018]] , 2019; [[#ICLEI--2019a|ICLEI 2019a]] ; [[#C40%20Cities--2020|C40 Cities 2020]] a).

'''•''' More than 360 cities announced at the Paris Climate Conference that the collective impact of their commitments will lead to a reduction of up to 3.7 GtCO 2 -eq (CO 2 -equivalent) of urban emissions annually by 2030 ( [[#Cities%20for%20Climate--2015|Cities for Climate 2015]] ).

'''•''' The Global Covenant of Mayors (GCoM), a transnational network of more than 10,000 cities, has made commitments to reduce urban GHG emissions by up to 1.4–2.3 GtCO 2 -eq annually by 2030 and 2.8–4.2 GtCO 2 -eq annually by 2050, compared to business-as-usual ( [[#GCoM--2018|GCoM 2018]] , 2019).

• More than 800 cities have made commitments to achieve net-zero GHG emissions, either economy-wide or in a particular sector (NewClimate Institute and Data-Driven EnviroLab 2020).

Although most cities and other subnational actors are yet to meet their net-zero GHG or CO 2 emissions commitments, the growing numbers of those commitments, alongside organisations enabled to facilitate reaching those targets, underscore the growing support for climate action by city and other subnational leaders.

<div id="8.1.1.2" class="h3-container"></div>

<span id="historical-and-future-urban-emissions"></span>
==== 8.1.1.2 Historical and Future Urban Emissions ====

<div id="h3-2-siblings" class="h3-siblings"></div>

One major innovation in this Assessment Report is the inclusion of historical and future urban GHG emissions. Urban emissions based on consumption-based accounting by regions has been put forth for the time frame 1990–2100 using multiple datasets with projections given in the framework of the Shared Socio-economic Pathway (SSP)–Representative Concentration Pathway (RCP) scenarios. This advance has provided a time dimension to urban footprints considering different climate scenarios with implications for urban mitigation, allowing a comparison of the way urban emissions and their reduction can evolve given different scenario contexts (see Glossary for definitions of various ‘pathways’ and ‘scenarios’ in the context of climate change mitigation, including ‘SSPs’ and ‘RCPs’).

<div id="8.1.1.3" class="h3-container"></div>

<span id="sustainable-development-linkages-and-feasibility-assessment"></span>
==== 8.1.1.3 Sustainable Development Linkages and Feasibility Assessment ====

<div id="h3-3-siblings" class="h3-siblings"></div>

Special emphasis is placed on the co-benefits of urban mitigation options, including an evaluation of linkages with the SDGs based on synergies and/or trade-offs. Urban mitigation options are further evaluated based on multiple dimensions according to the feasibility assessment (see [[#8.5.5|Section 8.5.5]] and Figure 8.19, and Section 8.SM.2) indicating the enablers and barriers of implementation. These advances provide additional guidance for urban mitigation.

<div id="8.1.2" class="h2-container"></div>

<span id="preparing-for-the-special-report-on-cities-and-climate-change-in-ar7"></span>