182 CHAPTER 7 Human Population Change and the Environment
© mediacolor’s/AlamyMost cities have blocks and blocks of brownfields—areas
of abandoned, vacant factories, warehouses, and resi-
dential sites that may be contaminated from past uses
(Figure 7.21). Meanwhile, the suburbs continue to ex-
pand outward, swallowing natural areas and farmland.
Reuse of brownfields is complicated because many
have environmental contaminants that must be cleaned
up before redevelopment can proceed. Nonetheless,
brownfields represent an important potential land
resource. Pittsburgh is known for its redevelopment of
brownfields that were once steel mills and meatpacking
centers. Residential and commercial sites now occupy
several of these former brownfields (Figure 7.22).
Most workers in U.S. cities have to commute dozens
of miles through traffic-congested streets from the sub-
urbs where they live to downtown areas where they work.
Because development is so spread out in the suburbs,
having automobiles is a necessity to accomplish everyday
chores. This heavy dependence on motor vehicles as our
primary means of transportation increases air pollution
and causes other environmental problems.
The high density of automobiles, factories, and com-
mercial enterprises in urban areas causes a buildup of
airborne emissions, including particulate matter (dust),to race, ethnicity, religion, and socioeconomic status than
populations in rural areas. People living in urban areas
tend to be younger than those living in the surrounding
countryside. The young age structure of cities is due to
the influx of many young adults from rural areas.
Urban and rural areas often differ also in their pro-
portions of males and females. Cities in developing na-
tions tend to have more males. In cities in Africa, for
example, males migrate to the city in search of employ-
ment, whereas females tend to remain in the country and
tend their farms and children. Cities in highly developed
countries often have a higher ratio of females to males.
Women in rural areas there often have little chance of
employment after they graduate from high school, so they
move to urban areas.
Environmental Problems
of Urban Areas
Growing urban areas affect land-use patterns. Subur-
ban sprawl that encroaches into former forest, wetland,
desert, or agricultural land destroys or fragments wild-
life habitat. Portions of Chicago, Boston, New York City,
and New Orleans, for example, are former wetlands.
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ÕÃiÃÊ>`ÊÃÌÀiÃÊUÊ}ÕÀiÊÇ°Ó£ÊWhy are brownfields such a problem
in developed countries?Think Critically