Environmental Engineering Reference
In-Depth Information
Effects of Gases in the Atmosphere: The
Natural Greenhouse Effect
Water vapor, carbon dioxide, and other gases
influence climate by warming the lower troposphere
and the earth's surface.
Small amounts of certain gases in the atmosphere play
a key role in determining the earth's average tempera-
tures and thus its climates. These gases include water
vapor (H
2
O), carbon dioxide (CO
2
), methane (CH
4
),
and nitrous oxide (N
2
O).
These
greenhouse gases
allow mostly visible light
and some infrared radiation and ultraviolet (UV) radi-
ation from the sun to pass through the troposphere.
The earth's surface absorbs much of this solar energy
and transforms it into longer-wavelength infrared ra-
diation (heat), which then rises into the troposphere.
Some of this heat escapes into space, but some is
absorbed by molecules of greenhouse gases and emit-
ted into the troposphere as even longer-wavelength in-
frared radiation. Some of this released energy radiates
into space, and some warms the troposphere and the
earth's surface. This natural warming effect of the tro-
posphere is called the
greenhouse effect
(Figure 5-5,
p. 82). Without its current greenhouse gases (especially
water vapor, which is found in the largest concentra-
tion), the earth would be a cold and mostly lifeless
planet.
Human activities such as burning fossil fuels,
clearing forests, and growing crops release carbon
dioxide, methane, and nitrous oxide into the atmo-
sphere. Considerable evidence and climate models in-
dicate that these large inputs of these greenhouse gases
into the troposphere can enhance the earth's natural
greenhouse effect and lead to
global warming.
This
could alter precipitation patterns, shift areas where we
can grow crops, raise average sea levels, and change the
areas where some types of plants and animals can live.
Cell 3 North
Cold,
dry air
falls
Moist air rises — rain
Polar cap
Cell 2 North
Arctic tundra
Evergreen
coniferous forest
Temperate deciduous
forest and grassland
60
°
Cool, dry
air falls
Desert
Cell 1 North
30
°
Moist
air rises,
cools, and
releases
moisture
as rain
Tropical deciduous forest
Tropical
rain forest
0
°
Equator
Tropical deciduous forest
30
°
Desert
Cell 1 South
Temperate deciduous
forest and grassland
Cool, dry
air falls
60
°
Cell 2 South
Polar cap
Cold,
dry air
falls
Moist air rises — rain
Cell 3 South
Figure 5-4
Natural capital:
global air circulation and biomes.
Heat and moisture are distributed over the earth's surface by
vertical currents, which form six giant convection cells at
different latitudes. The direction of air flow and the ascent and
descent of air masses in these convection cells determine the
earth's general climatic zones. The uneven distribution of
heat and moisture over the planet's surface leads to the
forests, grasslands, and deserts that make up the earth's
biomes.
encing climate and vegetation, especially near coastal
areas. They also help mix ocean waters and distribute
the nutrients and dissolved oxygen needed by aquatic
organisms.
The warm Gulf Stream (Figure 5-2), for example,
transports 25 times more water than all of the world's
rivers combined. Without the warming effect of the
heat carried northward from the equator, the climate
of northwestern Europe would be subarctic to arctic. If
this ocean current suddenly stopped flowing, deserts
would appear in the tropics and thick ice sheets would
cover northern Europe, Siberia, and Canada.
Witness the greenhouse effect and see how human activity
has affected it at Environmental ScienceNow.
Topography of the Earth's Surface
and Local Climate: Land Matters
Interactions between land and oceans, as well as
disruptions of air flows by mountains and cities, affect
local climates.
Heat is absorbed and released more slowly by water
than by land. This difference creates land and sea
breezes. As a result, the world's oceans and large lakes
moderate the climate of nearby lands.
Various topographic features of the earth's surface
create local and regional climatic conditions that differ
from the general climate of a region. For example,
Learn more about how oceans affect air movements, near
where you live and all over the world, at Environmental
ScienceNow.
