Urbanization and Environmental Sustainability

by Crystal Davis

Earth Trends - Feb 25, 2008

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Now home to half of the world's people, cities are increasingly at the forefront of our most pressing environmental challenges. While the current pace of urbanization is not unique in human history, the sheer magnitude of urban growth--driven by massive demographic shifts in the developing world--is unprecedented, with vast implications for human well-being and the environment. However, where cities pose environmental problems, they also offer solutions. As hotspots of consumption, production, and waste generation, cities possess unparalleled potential to increase the energy efficiency and sustainability of society as a whole.

Global Urbanization Trends

Cities generate a disproportionate share of gross domestic product (GDP) and provide, on average, greater social and economic benefits to their inhabitants than do rural areas. As a result, increased urbanization often correlates to higher national incomes (see Figure 1).

Figure 1: Economic and Social Welfare in Urban vs Rural Areas

Source: EarthTrends, 2008

 

Among industrialized nations, city dwellers already account for nearly three-quarters of the population and will grow in number by less than half a percent per year through 2030, while the rural population will actually decline (UN, 2008). Cities of the developing world, on the other hand, will absorb roughly 95 percent of the total population growth expected worldwide in the next two decades, a result of rural to urban migration, the transformation of rural settlements into urban places, and natural population increases (see Figure 2). All together, over 1.5 billion residents will be added to developing country cities by 2030, many of whom will be poor. Already, one of every three city dwellers lives in slum conditions (UN-Habitat, 2006).

At the global level, these demographic shifts define a remarkable urban transition. By 2030, five billion people (60 percent of the global population) will live in cities and four-fifths of these urban dwellers will be in the developing world. Megacities--those with more than ten million inhabitants--will continue to grow in size and number, albeit slowly, especially in developing countries. The most rapid growth will occur in cities with fewer than half a million residents, which collectively account for over half of the world's urban dwellers.

Figure 2: Population Growth and Urbanization, 1950-2030

Source: EarthTrends, 2008

 

Environmental Challenges in an Urban Society: Local vs Global Issues

Along with the many social and economic benefits of urbanization comes a plethora of environmental ills, some of staggering proportion. Cities span less than three percent of the world's land area, but the intense concentration of population, industry and energy use can lead to severe local pollution and environmental degradation. Furthermore, a city's ecological footprint extends far beyond its urban boundaries to the forests, croplands, coal mines and watersheds that sustain its inhabitants.

In the cities of the developing world, where population growth has outpaced the ability to provide vital infrastructure and services, the worst environmental problems are experienced close to home, with severe economic and social impacts for urban residents. Inadequate household water supplies, waste accumulation, and unsanitary conditions exact an enormous toll on the world's one billion slum dwellers in terms of unnecessary death and disease. Developing country cities also experience the world's worst urban air pollution as a result of rapid industrialization and increased motorized transport. Worldwide, urban air pollution is estimated to cause one million premature deaths each year and cost two percent of GDP in developed countries and five percent in developing countries (UNEP, 2008).

While cities in wealthier countries have already adopted policies and technologies to rectify many of their local environmental problems, there is a growing realization that human activities in urban areas can have significant impacts on a global level as well. In fact, the world's cities account for 75 percent of global energy consumption, 80 percent of greenhouse gas (GHG) emissions, and a disproportionate share of resource use, such as food, timber, and steel (UN-Habitat, 2007).

City dwellers in wealthy countries, characterized by some of the highest per capita levels of consumption in the world, are largely responsible for these trends. While an American city with a population of 650,000 requires approximately 30,000 square kilometers of land to service its needs, a similar sized but less affluent city in India requires only 2,800 square kilometers (UNEP, 2005). Similarly, urban residents in the developed world generate up to six times more waste than those in developing countries.

However, developing countries are becoming wealthier and more urban, bringing their consumption levels closer to those of the developed world. As a result, they are fast becoming significant contributors to the global problems of resource depletion and climate change (see Figure 3). The need to make cities more efficient and less polluting is hence more urgent than ever before.

Figure 3: Per Capita Resource Consumption: Current vs Trends

Source: EarthTrends, 2008

 

Potential for Sustainable Cities

Cities present one of the great environmental challenges of the 21st century, yet they also have an unrivaled capacity to absorb large populations sustainably and efficiently. With proper planning and long-term vision, dense settlement patterns offer economies of scale that can actually reduce pressures on natural resources from population growth and increase energy efficiency. Because people live close together and need less space in cities, each person requires less critical infrastructure like sewers, electricity, and roads than in suburbs or other decentralized human settlements. Innovations in building construction, energy efficiency, waste management, and transportation are just a few of the ways that we can make cities mores sustainable.

 

Box 1: Innovations in Urban Mobility

Growth in both motorization and traffic congestion in cities affects both productivity and human health; each year nearly a million people die as a result of outdoor air pollution. In addition, road transport accounts for roughly 15 percent of global greenhouse gas emissions, excluding land use change (CAIT, 2004). City planners in both developed and developing countries are responding to this problem, particularly in urban areas, by leveraging the unique economies of scale that cities can provide. Some examples include:

Communal bicycles in Paris. For a few Euros residents can pick up a bike at one of the new docking stations all over the city, ride it and drop it off at their destinations. In a few years the city will have a similar system using 2,000 electric-powered cars. These two initiatives are designed to reduce car traffic by 40 percent by 2020.

Congestion pricing in London. Automobiles must pay a fee to drive in London's central area during weekdays to reduce traffic congestion. Mayor Ken Livingston has also pedestrianized certain downtown streets, soon to become tree-line walkways.

Innovative policies in Bogota. Bogota, Columbia has restricted traffic during peak hours to reduce rush hour traffic by 40 percent. They have an annual car-free day, the only one of its size that actually enforces a ban on private cars. A few years ago Bogota also increased the gasoline tax, and poured half the resulting revenues into Transmilenio, a bus system that currently serves 500,000 of the city's residents every day.

 

At the forefront of the sustainable cities movement are some of the modern world’s oldest cities like Paris, London, and New York. In New York, for example, per capita GHG emissions are now just one-third of the U.S. average (CNN, 2007). These efforts serve as models for cities in the developing world as they undergo massive growth and change. Since these cities are still at an early stage in their development, there exists great potential for sustainable urban planning, but there is also an enormous threat if early action is not taken.

Given increasing responsibilities and limited funds, however, city governments must make strategic choices about which environmental and social problems to tackle first. This will require balancing immediately pressing environmental problems such as water and sanitation with long-term concerns such as energy use and climate change, while also reconciling the often competing demands of economic growth and environmental protection. The choices made in cities today will help determine the extent to which urbanization will be a positive force for human development and the future of the global environment.

© 2007 World Resources Institute

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