Environmental Engineering Reference
In-Depth Information
To do science is to search for repeated patterns, not simply to
accumulate facts, and to do the science of geographical ecology
is to search for patterns of plant and animal life that can be
put on a map.
R
OBERT
H. M
AC
A
RTHUR
Weather
is an area's short-term temperature, precipita-
tion, humidity, wind speed, cloud cover, and other
physical conditions of the lower atmosphere over a
short period of time. Science Supplement 5 at the end of
this topic introduces you to weather basics.
Climate
is a region's general pattern of atmo-
spheric or weather conditions over a long time.
Aver-
age temperature
and
average precipitation
are the two
main factors determining climate. Figure 5-2 (p. 80) de-
picts the earth's major climate zones.
Many factors contribute to the global and local cli-
mate. The main ones are the amount of solar radiation
reaching the area, the earth's daily rotation and annual
path around the sun, air circulation over the earth's
surface, the global distribution of landmasses and
seas, the circulation of ocean currents, and the eleva-
tion of landmasses.
Three major factors determine how air circulates
over the earth's surface. The first factor is the
uneven
heating of the earth's surface.
Air is heated much more at
its fattest part, the equator, where the sun's rays strike
directly, than at the poles, where sunlight strikes at a
slanted angle and spreads out over a much greater
area. You can observe this effect by shining a flashlight
in a darkened room on the middle of a spherical object
such as a basketball and moving the light up and
down. The differences in the amount of incoming solar
energy help explain why tropical regions near the
equator are hot, polar regions are cold, and temperate
regions in between generally have intermediate aver-
age temperatures.
A second factor is the
rotation of the earth on its
axis
—an imaginary line connecting the north and south
poles. As the earth rotates around its north-south axis,
its equator rotates faster than its polar regions. As a re-
sult, the air masses rising above the earth and moving
north and south are deflected to the west or east over
different parts of the planet's surface (Figure 5-3, p. 80).
The direction of air movement in these cells sets up
belts of
prevailing winds
—major surface winds that
blow almost continuously and distribute air and mois-
ture over the earth's surface.
The third factor affecting global air circulation is
properties of air, water, and land.
Heat from the sun evap-
orates ocean water and transfers heat from the oceans
to the atmosphere, especially near the hot equator.
Also, the earth's landmasses give up heat faster than
its oceans. These properties create giant cyclical con-
vection cells that circulate air, heat, and moisture both
vertically and from place to place in the troposphere.
The earth's air circulation patterns, prevailing winds,
and mixture of continents and oceans result in six giant
convection cells—three north of the equator and three
south of the equator—in which warm, moist air rises
and cool, dry air sinks. This leads an irregular distribu-
tion of climates and patterns of vegetation, as shown in
Figure 5-4 (p. 81).
This chapter provides an introduction to the earth's
climate and how it affects the types of life found in
different parts of the earth. It discusses addresses
these questions:
What key factors determine the earth's climate?
■
How does climate determine where the earth's
major biomes are found?
■
What are the major types of desert and grassland
biomes, and how do human activities affect them?
■
What are the major types of forest and mountain
biomes, and how do human activities affect them?
■
What are the major types of saltwater life zones,
and how do human activities affect them?
■
What are the major types of freshwater life zones,
and how do human activities affect them?
■
KEY IDEAS
■
Climate is an area's average weather conditions—
especially temperature and precipitation—over a long
time.
■
The climate of a region is determined by incoming
solar radiation, global patterns of air and water move-
ment, gases in the atmosphere, and major features of
the earth's surface.
■
The location of terrestrial biomes such as deserts,
grassland, and forests is determined mostly by climate
and human activities that remove or alter vegetation.
■
Saltwater and freshwater aquatic life zones cover
almost three-fourths of the earth's surface.
■
Human activities are disrupting and degrading
many of the ecological and economic services pro-
vided by the earth's terrestrial biomes and aquatic
systems.
5-1
CLIMATE: A BRIEF INTRODUCTION
Factors That Affect Climate
Climate is the average weather conditions—especially
temperature and precipitation—of an area over a long
time. It is affected by global air circulation.
