Cities
Cities are home to more than half the global population, and another 2.4 billion people are expected to live in urban areas by 2050. Cities bring benefits to people and the planet, such as economic opportunities and social capital. However, traditional models of city development can result in congestion, sprawl, pollution and inequality. Achieving sustainable, human-centered urban growth and a thriving urban future for all is a crucial global challenge.
Between 2015 and 2050, the world’s urban population is expected to continue to increase. Ninety percent of new urban inhabitants will live in Asia and Africa. This signifies a rapid shift in land and resource use and urban geography.
Significant investment in new infrastructure will be required to meet population growth and shifts. Annual infrastructure investment will need to double by 2040 and building floor area will nearly double by 2050.
How a city’s economic growth and investment keeps pace (or does not) with its population growth provides important insights into how well prepared it is for meeting the needs of growing numbers of residents. This capacity varies significantly across cities. Cities categorized as “struggling” and “emerging” have relatively lower GDP per capita relative to their infrastructure needs. “Thriving” and “stabilizing” cities in contrast have more resources available to meet infrastructure needs. Struggling cities are projected to experience more rapid population growth than economic growth, leaving them with fewer resources to provide for their residents.
As cities grow outward, peripheral land use is being shifting from agriculture and natural lands to settlements, putting pressure on food production and in turn on ecosystems as agriculture moves into previously natural, and often less productive, lands.
Growing consumption in cities is impacting the ecological health of neighboring regions. Urban areas are responsible for about two-thirds of energy use and 60% of domestic raw material consumption, and the rate of consumption is increasing. Cities impact faraway places through global markets and trade. Much of our understanding comes from national-level data; understanding these flows to and from subnational units is an important avenue of research.
Seventy percent of city residents in developing countries lack one or more basic services, such as clean water, sanitation or electricity. And credible evidence suggests that these estimates may significantly understate the problems. Cities need to better provide core services to all residents.
Growing populations, sprawl and increased demand for mobility can lead to congestion, which constrains productivity, and safety risks. More than 1.35 million people die in road traffic crashes annually, a number that is growing globally.
Demand for water in cities is projected to increase 50-70% in the next 30 years, while drought and other water stress is also projected to increase.
Increased extreme precipitation events and sea level rise from climate change have cost billions of dollars in damages, with the potential for displacing hundreds of millions of people, especially from coastal cities.
The physical changes caused by urbanization and the intensity of fuel combustion for energy, which emits heat and pollutants, can result in poor air quality and higher temperatures in cities. Urban environments have less vegetative cover more impervious surfaces, like pavement and roofs, which retain heat makes cities hotter than surrounding areas. This is called the urban heat island effect.
Higher global temperatures from climate change are exacerbating air pollution and urban heat extremes, increasing the danger to vulnerable populations. Air pollution is now the world’s number one environmental health risk, linked to more than 7 million deaths every year.
While some urban expansion is inevitable, cities should make deliberate efforts towards more compact, connected and more equitable land development. More efficient use of land improves access to services at significantly lower costs for cities and households and reduces the environmental impact of urbanization.
Cities are increasingly turning to improved public transportation, such as bus rapid transit, and experimenting with shared, electric and micro-mobility solutions to avoid the high costs and inequities of personal vehicle-based development. These urban mobility systems increase access to opportunity and services with lower costs.
Cities can use resources more efficiently than rural areas because of their more compact form and economies of scale. This reduces the environmental impacts of cities while increasing accessibility and affordability for residents. Adopting clean and renewable energy, green infrastructure and technologies to improve resource efficiency and reuse of waste can all reduce the environmental impacts of cities, while improving productivity. Some cities are more efficient with resource management than others but all have opportunities to improve. The pace of progress in improving efficiency so far has been too slow to meet the Paris agreement on climate change.
Open information can make city decision-making more responsive and transparent. For example, providing open access to data on public transit service stops, routes and schedules using the General Transit Feed Specification (GTFS) can make transit easier to use for riders and improve a city's ability to plan for a more equitable transportation network. Unfortunately, most cities in Asia, South America and Africa lack this open data.
Cities are highly productive places and provide a focal point for social and economic development. Energy, land and material consumption depends largely on the size and performance of the global built environment, which is growing rapidly. The choices made by cities and national governments on urban development today play a huge role in the successes or failures of sustainable human development in the decades ahead, including the Sustainable Development Goals, the United Nations’s New Urban Agenda and the Paris Agreement on climate change.
Cities are responsible for around 70% of global greenhouse gas emissions. Actions that make cities more affordable, equitable and productive – such as providing information on public transportation or providing clean energy sources – can also reduce city contributions and vulnerability to climate change. Many cities are now working to achieve these objectives together through low-carbon and resilient growth.