Defining an urban settlement solely by its administrative boundary ignores the many connections and flows that make the city possible. Achieving Sustainable Development Goal (SDG) 11 on urban sustainability requires an approach that considers these telecouplings (Seto et al. 2012; Seto et al. 2017; Haase 2019). Changes in social, economic, environmental and political conditions will create new connections and remove, strengthen or weaken existing ones (Güneralp, Seto and Ramachandran 2013). In other instances, global investment, supply chains and consumption patterns in one area can change relationships in others (United Nations Environment Programme [UNEP] 2019, chapters 3 and 8). All this means cities can be thought of as nodes in a network, where the intensity of connections with near and faraway places changes with time and across space (Glaeser, Ponzetto and Zou 2016; Cities Alliance 2019).2
As cities grow, many dependencies with other areas may be overlooked and their environmental impact could increase at the expense of the city’s needs and the well-being of its dwellers. The pressure of urban growth also affects inhabitants of other areas and nature’s contributions to human well-being. City planners and practitioners need to be on the alert for signs of these trade-offs and must remember that the environmental dimensions of urban sustainability are tied to the areas connected to the city (section 5.4.2). Failing to consider these urban telecouplings makes it extremely difficult to achieve SDG 11 targets and many other SDGs, as pressures and impacts are also connected through these links between cities and rural areas, natural resources and other cities.
Urban settlements vary tremendously in their social, economic, environmental, political and technological contexts. All cities are already facing the impacts of climate change and its associated effects on human well-being. However, impacts – both present and future – depend on context and characteristics. For example, coastal cities may need to plan for rising sea levels, while cities in arid regions may experience water shortages due to changes in precipitation patterns. (Revi et al. 2014; C40 Cities Climate Leadership Group 2020; Grimmond et al. 2020). As discussed in chapter 2, size, institutional arrangements and income levels will determine the capacities of individual cities to cope with these challenges (Anguelovski, Chu and Carmin 2014; Reckien et al. 2015; Estrada, Botzen and Tol 2017; Paterson et al. 2017). Variations in urban conditions throughout the world mean there is no single silver bullet for city planners and managers (Brelsford et al. 2017). Unpacking the complexity of managing urban settlements is an urgent task, since urbanization is forecast to accelerate in all regions, albeit at different rates (United Nations 2019). Cities need to adopt integrated, synergistic, resilient and adaptive strategies for urban environments to meet the SDGs and other commitments, such as those related to the Intergovernmental Panel on Climate Change (IPCC) 2018 report on the impacts of global warming, the
2 Examples of specific telecouplings are discussed later in the chapter.
Paris Agreement and the Post-2020 Global Biodiversity Framework (Bazaz et al. 2018; Organization for Economic Co-operation and Development [OECD] 2020).
This chapter presents the most relevant issues of this urban–environment nexus, based on the five environmental themes of the Global Environment Outlook report: air, biodiversity, land and soil, oceans and coasts, and freshwater (UNEP 2019). However, we must acknowledge that the interconnected nature of cities and the environment means their impact on one area might also affect others. What may appear as repetitions in the text, in fact reflect the integrated nature of this nexus. Section 3.2 describes the main impacts of environmental change on cities, while section 3.3 emphasizes how they contribute to environmental change and how the interact with each other. Section 3.4 synthesizes the most important impacts at the city scale, provides possible global trends and reflects on gaps in the available data. Section 3.5 explores how changes in the city and the environment affect the health and well-being of urban residents. Finally, the chapter closes by highlighting the urgent need for more sustainable urban environments with more integrated and inclusive governance structures.
3.2 How are global environmental changes affecting cities?
As the environment changes across the globe, some of the conditions under which cities have developed and functioned are being transformed. For example, many urban settlements at higher altitudes in Africa and Latin America were free of the dengue virus as they remained above the temperature threshold for the vectors of this disease. However, rising global temperatures have made some of these cities warm enough for the dengue fever vector Aedes aegypti to thrive (Lozano-Fuentes et al. 2012; Equihua et al. 2017). This shows how a global change can affect cities locally. The GEO-6 report highlights five drivers of environmental degradation: population growth; urbanization; economic development; technology; innovation and sustainability; and climate change. Figure 3.2 uses the Driver–Pressure–State–Impact–Response framework to illustrate how these drivers impact cities and highlights how the environmental and city-level impacts can result from the interaction of several driving forces. The remainder of this section examines in more detail how global environmental changes are affecting cities across each of the five dimensions.
3.2.1 Air
The atmosphere has no boundaries and its patterns of circulation make it one of the primary integrators of the Earth system. This means that global environmental changes – both near and far – impact the air quality and climate of cities. Emissions of greenhouse gases and short-lived climate forcers from human and natural sources warm the atmosphere, resulting in significant impacts on cities (IPCC 2018). Emissions of carbon dioxide (CO2
especially from the burning of fossil fuels, industry and land- The State of the Environment in Cities 45
) into the atmosphere,
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