Botkin Environmental Science Earth as Living Planet 8th txtbk

1.5 An Urban World 11
history of life on Earth, life has profoundly changed the
global environment, and that these changes have tended
to improve the chances for the continuation of life. Because
life affects the environment at a global level, the environment
of our planet is different from that of a lifeless
one.
1.5 An Urban World
In part because of the rapid growth of the human population
and in part because of changes in technology, we are
becoming an urban species, and our effects on the environment
are more and more the effects of urban life (Figure
1.11a). Economic development leads to urbanization;
people move from farms to cities and then perhaps to
suburbs. Cities and towns get larger, and because they are
commonly located near rivers and along coastlines, urban
sprawl often overtakes the agricultural land of river floodplains,
as well as the coastal wetlands, which are important
habitats for many rare and endangered species. As urban
areas expand, wetlands are filled in, forests cut down, and
soils covered over with pavement and buildings.
In developed countries, about 75% of the population
live in urban areas and 25% in rural areas, but in developing
countries only 40% of the people are city dwellers. By
2008, for the first time, more than half of the people on
Earth lived in urban areas, and it is estimated that by 2025
almost two-thirds of the population—5 billion people—
will live in cities. Only a few urban areas had populations
(a)
FIGURE 1.11 (a) An urban world and
a global perspective. When the United
States is viewed at night from space, the
urban areas show up as bright lights. The
number of urban areas reflects the urbanization
of our nation. (b) Megacities by
2015. (Source: Data from United Nations
Population Division, World Urbanization
2005, and State of the World 2007. World
Watch Institute.)
Population (million)
40
35
30
25
20
15
10
5
0
Tokyo
Mumbai
Mexico City
São Paulo
New York
Delhi
Shanghai
Kolkata
Dhaka
Jakarta
Lagos
Karachi
Buenos Aires
Los Angeles
Cairo
Manila
Rio de Janeiro
Beijing
Osaka
Istanbul
Source: United Nations
2015
2005
1990
1950
Moscow
Guangzhou
(b)