Fifteen Eighty Four

1. How do cities influence environmental change far beyond their own boundaries

There are two major mechanisms through which cities influence environmental change. First, cities influence environmental change by generating pollutants and other environmental pressures that can extend far beyond their boundaries. Urban areas release large amounts of CO₂, NOx, particulate matter, and other pollutants into the atmosphere, altering its composition not only locally but also at considerable distances. Similarly, poorly treated sewage and urban runoff can carry excessive nutrients, pharmaceuticals, heavy metals, and other contaminants into rivers and coastal waters. Winds, river flows, and ocean currents can then disperse these urban-born substances across much larger areas. Cities also generate substantial amounts of excess heat through traffic, buildings, industrial activities, and air conditioning, contributing to the urban heat island effect and, at larger scales, potentially influencing regional climate.

Second, modern cities are not self-sufficient, but depend heavily on the world beyond them to meet their resource needs. This is partly because urban areas consume large amounts of water, food, energy, and raw materials, while having very limited capacity to produce or replenish these resources themselves. High levels of air, soil, and water pollution can further constrain local resource availability, making nearby water sources or agricultural land unsuitable for human use or food production. As a result, urban dwellers depend on water, food, construction materials, and energy imported from surrounding regions or even from thousands of kilometers away. This dependence effectively shifts part of the environmental burden of urban consumption elsewhere. These imports can also deplete resources elsewhere and cause environmental damage that may be difficult or impossible to reverse.

2. Why should we think of cities as ecosystems rather than simply built environments?

Cities, like other ecosystems, are composed of multiple interacting components such as vegetation, soils, aquifers, and animals. They also include the built environment, vehicles, and people. Urban ecosystems differ from other ecosystems in several important ways in terms of their structure and function, while also sharing many fundamental similarities. For instance, underground structures in urban ecosystems are generally deeper than those in non-urban ecosystems, yet there are similarities in the purposes for which these structures are built.

3. Can cities become part of the solution to the climate and biodiversity crises?

Cities can definitely become part of the solution to the climate crisis. They are responsible for a large share of global CO₂ emissions, which contribute to global climate change. The heat stored and released by the built environment and urban transportation also impacts local climate conditions. At the same time, cities have considerable potential to address these challenges through lower energy consumption, low-carbon transportation, green space expansion, and other measures that reduce heat storage and carbon and heat emissions, while increasing resilience to climate change.

Cities can also play a role in the biodiversity crisis. Urban areas are often associated with habitat loss and environmental degradation. However, they can also provide diverse habitats for a wide range of species. Parks, gardens, urban forests, wetlands, and even the built environment can support plants, insects, birds, and other wildlife. Cities can also serve as refuges for rare plant species that have disappeared from their natural habitats. By protecting and expanding these urban habitats, cities can contribute to the conservation of biodiversity and provide important spaces for species to survive and recover. Shrinking cities also create special sites that foster biodiversity. The diverse communities born in urban settings are likely to differ markedly from the ones formed in natural ecosystems.

4. What are the most important tools for understanding the environmental impacts of cities?

Both monitoring of urban ecosystems and numerical modelling are crucial for understanding the environmental impacts of cities.  Monitoring of urban environmental impacts should be expanded from the local scale, where most measurements are currently made, to regional and global scales, where substantially less data exist. These observations should include monitoring impacts on the atmosphere, water, and land both when cities extract and consume resources and when they generate and dispose of waste. In addition, numerical modelling is important as it helps to understand the complex impacts and predict how they might change in the future. For instance, how transformations of urban form, building design, and increasing urban vegetation cover influence environmental impacts and at what spatial and temporal scales.

5. What does a truly sustainable city look like, and how can we get there?

In answering this question, I will focus on the environmental dimension of a sustainable city, as this is where my expertise lies. Social and economic dimensions are equally important to urban sustainability, but they fall outside the scope of my expertise and will therefore not be addressed in detail here. Historically, cities were closely tied to the resources available in their surroundings. They depended largely on local supplies of water, food, energy, and building materials and, ideally, used them in ways that did not undermine the ability of future generations to meet their own needs. The earliest cities, however, developed mainly in subtropical regions, where favourable environmental conditions supported this way of life. Over time, urban growth continued in increasingly challenging environments, such as deserts, floodplains, and seismically active regions. The survival of modern cities does not merely depend on local conditions and resources; it also requires sophisticated infrastructure and the long-distance transfer of water and other essential resources through global supply chains. Whether such cities can achieve environmental sustainability remains a fundamental question.

A truly sustainable city is the one that lives within the limits of its environment. It uses energy, water, land, and raw materials carefully and digests the pollution and waste it produces. Importantly, it also considers the environmental impacts associated with the resources it imports. Getting there requires considerable changes in how cities are planned, how buildings are designed and managed, and likely even where they are located. A city’s location matters because it determines the resources it requires, the environmental pressures it creates, and its vulnerability to natural hazards.

Urbanization and Global Environmental Change is available now. 9781108406574