Urban impacts on climate - The Global Climate System: Patterns, Processes, and Teleconnections - page 213

Chapter 7
Urban impacts on climate
7.1 Introduction
Anthropological research tells us that humans originally congregated in central
locations at important transport junctions, such as rivers, to trade goods, com-
municate, and to obtain information. Such locations eventually grew to villages,
then to towns, and then to cities as human populations expanded, and the
technology increased for buildings, roads, and so forth. Along with the expan-
sion of population and the growth to cities came modifications to the environ-
ment, including changes to the local and regional climate. Depending on the
state of development, cities are often noisy, smelly, polluted, densely packed,
and overpopulated, with major difficulties associated with waste, water, the
atmosphere, and human health. However, as Figure 7.1 shows, cities have
many benefits to populations, including providing shelter, employment, ser-
vices, technological development, education, cultural and social interactions,
and income. Therefore cities have become essential to the lifestyle and well-
being of human beings.
Spatially, cities cover less than 1.5% of the Earth's land surface. However, the
latest summary of the state of cities around the world from the United Nations
Environment Programme (GEO 2003 ) states that currently about 47% of the
world's population live in cities. This is almost double the percentage in 1975
(27%). Projections during the first half of the twenty-first century suggest an
average urban population growth of 2% per year, and that by 2050, 65% of the
global population will live in cities.
Much attention has been paid to the development of megacities, those with
populations of 10 million or more. Figure 7.2 shows there are 18 megacities,
with the majority in Asia. Here, urban growth rates are among the fastest in the
world. Tokyo/Yokohama is the largest city with over 26 million in population,
followed by Mexico City, Sao Paulo (Brazil), and Bombay (India). Virtually all
the megacities are located in developing countries, with the exception of Tokyo,
New York, and Los Angeles. According to GEO ( 2003 ), however, the majority
of urban dwellers live in medium to small sized cities and towns, locations that
do not attract much global attention.
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