Environmental Impacts of Cities

A city's urban environment—the area that it occupies—is directly affected by the city's use of materials, air, water, and land. A city's ecological footprint is the space needed to support the city, equivalent to the physical and biological regions disturbed to provide resources to the city and accept its wastes. A city's metabolism is the sum total of materials, fuels, water, and goods that flow into a city to sustain its populace and economy. Cities vary in size, from agglomerated urban settings of 5,000 people or more to megacities, agglomerated urban settings with more than 10 million people. Global cities are a subset of megacities, cities that set global economic and cultural trends. All cities influence the environment. Large cities tend to have a disproportionately greater environmental impact than less populous ones.

At the turn of the 21st century, cities occupied only 3% of Earth's land surface; however, their impacts extended across the globe. Cities’ voracious appetites for resources and their dispersal of pollutants into air, into water, and on land result in local, regional, national, and global environmental degradation. For example, in 2000, Los Angeles, California, had a population of about 4 million people and city limits covered an area of 1,290 square kilometers. The Los Angeles metropolitan area had more than 12 million people, including Los Angeles and Orange counties. The greater Los Angeles area, a megacity, covered much of five counties and included more than 17 million people. Direct effects of Los Angeles within the five counties of the megacity are smog, displacement of native habitats, contamination of surface and unconfined ground waters, and deposition of litter on city streets and beaches. The megacity's direct environmental impacts on the Western United States include air pollutants that diminish visibility at national parks of the Intermountain West, mountains of landfills for urban waste, and diminished flow and increased salinity of the Colorado River. However, the direct impacts to the region are only the beginning of the megacity's environmental impacts. Coal-fired plants in the west and Midwest provide electricity to Los Angeles, with associated environmental effects of surface and underground mining, coal combustion, and waste disposal. Power plant emissions send sulfur dioxide across national boundaries, affecting Canada's forests. The impacts of cars driven in Los Angeles are not limited to their emissions. Materials for cars come from mines, chemical plants, manufacturing centers, and cities that dispose of wastes on land, in the air, and into water. Beyond the impacts on local, regional, and global physical and biological environments are the effects on local, regional, and global populaces to sustain the city's appetite for goods and services. Los Angeles is one of 24,000 urban areas globally. It can be argued that the uneven distribution and unequal per capita [Page 941]consumption of Earth's resources exemplified by Los Angeles exacerbate rifts among rich and poor nations and lead to war, famine, and pestilence.

Geographers study the webs of relationships among people, places, and environment. Almost every field of geography addresses an aspect of urban environmental geography, including physical geography, which explains (a) some of the reasons why cities are located where they are, such as regional resources and connectivity to transportation corridors, and (b) the probable consequences of urban development to Earth systems, and human geography, which explains (a) the growth of cities, by migration and natural increase, and (b) the probable consequences of urban development to social and behavioral systems.

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