Ch 4

Title Page Photo

“The temperature of the air at any time and at any
place in the atmosphere is the result of the
interaction of a variety of complex factors.”
factors.”
— McKnight and Hess, p. 75.

Vocabulary
• environmental laps e rate (p. 98) • therm al energy (p. 76)
• evaporation (p. 86) • therm al infrared radiation (p. 80)
• global warm ing (p. 102) • therm ometer (p. 76)
• greenhous e effect (p. 83) • transmission (p. 83)
• greenhous e gases (p. 83) • ultraviolet (UV) radiation (p. 79)
• heat (p. 76) • upwelling (p. 96)
• infrared radiation (p. 80) • visible light (p. 79)
• insolation (p. 80) • absorption (p. 81)
• isotherm (p. 99) • adiabatic cooling (p. 85)
• kinetic energy (p. 76) • adiabatic warming (p. 86)
• latent heat (p. 86) • advection (p. 85)
• longwave radiation (p. 80) • albedo (p. 87)
• ocean current (p. 94) • angle of incidence (p. 89)
• radiant energy (p. 78) • average annual temperature range
• radiation (emission) (p. 80) • (p. 102)
• reflection (p. 81) • average lapse rate (p. 98)
• scattering (p. 82) • condensation (p. 86)
• shortwave radiation (p. 80) • conduction (p. 84)
• specific heat (p. 92) • convection (p. 85)
• subtropical gyres (p. 95) • convection cell (p. 85)
• temperature (p. 76) • electromagnetic radiation (p. 78)
• temperature inversion (p. 98) • electromagnetic spectrum (p. 79)
• terrestrial radiation (p. 80) • energy (p. 75)

The Impact of Temperature on
the Landscape
• Long-run temperature
conditions affect the organic
and inorganic components of
the landscape.
– Animals and plants often
evolve in response to hot or
cold climates.
– Soil development is affected
by temperature, with repeated
fluctuations in temperature
being the primary cause of
breakdown of exposed
bedrock.
– Human-built landscape is
created in response to
temperature considerations.

1

Energy, Heat, and Temperature
• Energy— the capacity to do work and can take
on various forms, or anything that changes the
state or condition of matter.
– Forms of energy include kinetic energy, chemical
energy, and radiant energy.
– Energy occurs at the micro scale, causing the motion
of atoms and molecules.
• Molecules in all substances possess kinetic energy—the
energy of movement.
• The greater amount of energy added to a substance, the
greater the kinetic energy.

Temperature and Heat
• Temperature is a description
of the average kinetic energy
of the molecules in a
substance.
• Heat (AKA thermal energy) is
the energy that transfers from
one substance to another
because of temperature
differences.
– Heat is simply energy
transferred from an object with
a higher temperature to an
object with a lower
temperature.
– This decreases the internal
energy of the hotter object and
increases the internal energy
of the cooler one.

Measuring Temperature
• There are a number of instruments for measuring temperature.
– All work on the principle that most substances expand when heated,
calibrating this change in volume to measure temperature.
• There are three temperature scales used in the United States: the
Fahrenheit Scale, the Celsius Scale, and the Kelvin scale.

2

• Fahrenheit Scale is used by public weather reports from
the National Weather Service and the news media; few
other countries than United States use it.
• Celsius Scale is used either exclusively or
predominately in most countries other than United
States, which uses it for scientific work. It is slowly being
established to supersede the Fahrenheit scale.
– Celsius to Fahrenheit: degrees Fahrenheit = (degrees Celsius X
1.8) + 32º
– Fahrenheit to Celsius: degrees Celsius = (degrees Fahrenheit –
32º) /1.8

• Kelvin Scale is used
in scientific research,
but not by
climatologists and
meteorologists.
– Measures what are
called absolute
temperatures.
• Degrees Celsius =
degrees Kelvin -273º
• Degrees Kelvin =
degrees Celsius + 273º

Solar Energy
• Only Sun provides
important source of
energy for Earth’s
atmosphere.
– Solar energy consists of
electromagnetic waves,
which do not diminish in
intensity despite traveling
150 million kilometers (93
million miles) to Earth.
– Energy travels at speed of
light, so takes 8 minutes to
reach Earth.

3

Electromagnetic Radiation
• Wave length measured
by distance of crest of
one wave to crest of the
next.
• Electromagnetic
spectrum consists of
waves of various lengths;
only three areas of the
spectrum are important to
study of physical
geography:

Electromagnetic Radiation
• Visible light—0.4 to 0.7 micrometers; makes up only 3% of all
electromagnetic spectrum, but large portion of solar energy.
• Ultraviolet Radiation—0.01 to 0.4 micrometers; too short to be seen by
human eye; could cause considerable damage to living organisms if the
shortest ones reached Earth’s surface, but atmosphere filters out.
• Infrared Radiation —0.7 to 1,000 micrometers; too long to be seen by
human eye; emitted by hot objects and sometimes called heat rays; Earth
radiation is entirely infrared (sometimes called thermal infrared), but only
small fraction of solar radiation.

Insolation
• The total insolation (incoming
solar radiation) received at the
top of the atmosphere is
believed to be constant over
the period of a year.
– Solar constant—the fairly
constant amount of solar
insolation received at the top
of the atmosphere; equivalent
to 1372 watts per meter
square.
– Not all insolation stays in the
atmosphere; some is reflected
off the atmosphere and
bounces back to space.

4

Basic Heating and Cooling
Processes in the Atmosphere
• To understand how energy travels from
the Sun to Earth, it’s best to examine
how heat energy moves.
• Heat energy moves from one place to
another in three ways:
1. Radiation
2. Conduction
3. Convection

Radiation
• Radiation—process by which
electromagnetic energy emits
from an object; radiant energy
flows out of all bodies, with
temperature and nature of the
surface of the objects playing a
key role in radiation
effectiveness.
– Hot bodies are more potent
than cool bodies (and the hotter
the object, the more intense the
radiation and the shorter the
wavelength).
– Blackbody radiator—a body that
emits the maximum amount of
radiation possible, at every
wavelength, for its temperature.

Absorption
• Absorption—the ability of an object to
assimilate energy from the electromagnetic
waves that strike it.
– Different objects vary in their capabilities to absorb
radiant energy (and thus increase in temperature).
– Color plays a key role in an object’s absorption ability;
dark-colored surfaces more efficiently absorb the
visible portion of the electromagnetic spectrum than
light-colored surfaces.

5

Reflection
• Reflection—the ability of an object to
repel waves without altering either the
object or the waves.

Scattering
• Scattering—the process by
which light waves change in
direction, but not in
wavelength.
– Occurs in the atmosphere when
particulate matter and gas
molecules deflect wavelength
and redirect them.
– Sometimes when insolation is
scattered, the waves are diverted
into space; but most continue
through atmosphere in altered,
random directions.
• Amount of scattering depends on
wavelength of wave and the size,
shape, and composition of the
molecule or particulate.

Scattering
• Why is the sky blue?
– Rayleigh scattering causes shorter wavelengths of
visible light to be scattered.
– Violets and blues in the visible part of the spectrum
are shorter in wavelength than the oranges and reds.
– Shorter waves like violets and blues are more readily
scattered by the gases in the atmosphere, so they are
more likely to be redirected.
– And the sun appears reddish at sunrise and sunset
because the path of light through atmosphere is
longer, so most of the blue light is scattered out
before the light waves reach Earth’s surface.

6

Scattering
• When the atmosphere
contains large quantities
of larger particles, such
as suspended aerosols,
all wavelengths of visible
light are more equally
scattered.
– In such instances the sky
has a gray appearance.
– This process is called Mie
scattering
– Scattering can diminish the
intensity of solar radiation
striking Earth’s surface

Transmission
• Transmission—the
process by which
electromagnetic waves
pass completely through
a medium; ability of
objects to transmit these
waves varies greatly
according to their
makeup; also,
transmission depends on
the wavelengths
themselves.

Shortwave Radiation
• Shortwave radiation—radiation with
wavelength less than around 4 micrometers;
almost all solar radiation is shortwave.

7

Longwave Radiation

• Longwave radiation—radiation with wavelength
more than around 4 micrometers; all terrestrial
radiation is longwave.

04_18FB-C.jpg

NOAA-15 satellite image showing nighttime emission of outgoing longwave radiation (in W/m2).

The Greenhouse Effect
• The Greenhouse Effect is directly related
to how these different wavelengths are
transmitted through objects.

8

• Greenhouse effect —would be more appropriately
called atmospheric effect, because the warming of the
atmosphere is not the same as what happens in actual
greenhouses, as originally thought.
• Greenhouses stay warm because warm air is trapped
inside and does not mix with the cooler air outside, so it
does not dissipate.
• The warming up of the atmosphere is more similar to
what occurs in a closed automobile parked in the
sunlight.
• The window glass transmits shortwave radiation, which
is then absorbed by the upholstery.
• The car emits longwave radiation, which is not readily
transmitted through the glass.

• In the atmosphere, atmospheric gases, known as
greenhouse gases, transmit the incoming solar
shortwave radiation, which are absorbed by Earth’s
surface.
• They do not transmit the outgoing longwave terrestrial
radiation, but instead absorb it, then reradiate the
terrestrial radiation back toward the surface.
• Heat is then trapped in the lower troposphere.
• The most important greenhouse gas is water vapor,
followed closely by carbon dioxide, then to a lesser
degree by methane and some kinds of clouds.

• Without the greenhouse effect the average temperature
of Earth would be -15ºC as compared to its present
average of 15ºC.
• Although the greenhouse effect is necessary for life on
Earth, there has been a significant increase in
greenhouse gas concentration, especially carbon
dioxide, in Earth’s atmosphere.
• This increase is associated with human activity, such as
the burning of fossil fuels.
• This increase has been accompanied by a slight, yet
measurable increase in global temperature.

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Conduction
• Conduction—the movement of energy
from one molecule to another without
changes in the relative positions of the
molecules.
• It enables the transfer of heat between
different parts of a stationary body, or
from one object to a second object when
the two are in contact.
• Conduction does require molecular
movement, however.
• Although the molecules do not move
from their relative positions, they do
become increasingly agitated as heat is
added.

Conduction
• An agitated molecule will move and collide
against a cooler, calmer molecule, and through
this collision transfer the heat energy.
– Thus, heat energy is passed from one place to
another, without the molecules actually moving from
one place to another, just vibrating back and forth
from agitation.
• (Thus, it’s the opposite of convection.)
• Conduction ability varies with the makeup of the
objects; metals are excellent conductors in
comparison to earthy materials like ceramics.

Conduction
• Why does Earth’s land surface warm up during
day?
– Earth’s land surface is a good absorber, but it is not a
good conductor.
– Thus, although some of the warmth that the land
surface absorbs is transferred deeper underground
most stays on the surface and is transferred back to
the atmosphere.
– Air, however, is a poor conductor too, so only the air
layer touching the ground is heated very much
(unless wind circulates the heat).

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Conduction
• Why do you stay warmer on a dry day?
– Moist air is a slightly more efficient conductor
than dry air.
– The moist air will conduct heat away from
you, while dry air will let it stay in closer
contact.

Convection
• Convection—the transfer
of heat by a moving
substance (opposite of
conduction).
– Molecules actually move
from one place to another,
rather than just vibrating
from agitation.
– The principal action in
convection is vertical,
though there is some
horizontal movement.
– If your room is heated by a
radiator, you have
experienced convection.

Convection
• Heat caused the air to expand, thus become
less dense, so the warm air can rise. This
creates a convective circulation pattern:
– Heated air expands and moves upward in the
direction of lowest pressure.
– The cooler surrounding air then moves in to fill the
empty space, and the air from above moves in to
replace that cooler air.
• One ends up with an updraft of warm air, and a downdraft of
cool air.

11

Advection

• Advection —when a
convecting liquid or
gas moves
horizontally as
opposed to vertically
as in convection.

Adiabatic Cooling and Warming
• When air rises or descends, its pressure
changes, which in turn changes its temperature,
without needing an external source. Instead, the
temperature depends on the extent of molecular
collisions.

Expansion: Adiabatic Cooling
• Expansion: Adiabatic cooling—cooling
by expansion in rising air; rising air
expands because there is less air above it,
so less pressure exerted on it.
– The molecules spread over a greater volume
of space, which requires more energy. So the
molecules slow down and don’t collide as
much.

12

Compression: Adiabatic
Warming
• Compression: Adiabatic warming—
warming by contraction in descending air;
descending air contracts because there is
more pressure being exerted on it, thus
compressing the molecules in the air and
making them collide more frequently.

Latent Heat
• Latent heat—energy stored or
released when a substance
changes state; can result in
temperature changes in
atmosphere.
• Evaporation—liquid water
converts to gaseous water
vapor; it is a cooling process
because latent heat is stored.
• Condensation—gaseous
water vapor condenses to
liquid water; it is a warming
process because latent heat is
released.

– Energy budget of Earth and its atmosphere

– Fig. 4-18

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The Heating of the Atmosphere

• Why doesn’t Earth get progressively
warmer or cooler?
– Because in the long run there is an apparent
balance between the total amount of
insolation received by Earth and the total
amount of terrestrial radiation returned to
space.


• However, a closer look shows that the
atmosphere experiences a net gain of 14
units every year in terms of its annual
balance, which is the result of longwave
radiation being trapped in the atmosphere
by greenhouse gases.
– Without it, Earth would not store the heat
necessary for life.

• Outgoing energy from Earth also depends on
transport of latent heat from process of
evaporation. There is more water than land, so
more than three-fourths of sunshine hits water,
which evaporates moisture from bodies of water.
– Ultimately, atmospheric heating is a complicated
sequence that has many ramifications:
– Atmosphere is heated mostly from below than from
above;
– There is an environment of almost constant
convective activity and vertical mixing.

14

Albedo
• Albedo—ability of an object to reflect
radiation; in case of Earth, it relates to the
amount of solar radiation or insolation that
Earth scatters, or reflects back, into space.

http://img462.imageshack.us/img462/7179/albedo11il.jpg
High Albedo=high reflectivity
Albedo - percentage of solar radiation
reflected Low Albedo=high absorption

- fresh snow = 85-95%
- dry sand = 35-40%
- tropical forest = ~13%
- Earth’s average albedo = ~30%

Variations in Heating by Latitude
and Season
• Earth does not evenly distribute heat
through time and space; instead, there are
variations in its radiation budget that relate
to latitudinal and seasonal variations in
how much energy is received by Earth.
• These imbalances are among the
fundamental causes of weather and
climate variations, as they cause unequal
heating of Earth and its atmosphere.

15

Latitudinal and Seasonal
Differences
• There is unequal heating of different
latitudinal zones for three basic reasons,
angle of incidence, day length, and
atmospheric obstruction:

Angle of Incidence
• Angle of Incidence—the angle
at which rays from the Sun strike
Earth’s surface; always changes
because Earth is a sphere and
Earth rotates on own axis and
revolves around the Sun.
– Angle of incidence is the primary
determinant of the intensity of
solar radiation received on
Earth.
– Heating is more effective the
closer to 90°, because the more
perpendicular the ray, the
smaller the surface area being
heated by a given amount of
insolation.
– Angle is 90° if Sun is directly
overhead.
– Angle is less than 90° if ray is
striking surface at a glance.
– Angle is 0° for a ray striking
Earth at either pole.

Atmospheric Obstruction
• Atmospheric Obstruction—clouds, particulate matter, and gas
molecules absorb, reflect, or scatter insolation.
– How much effect they have depends on path length, the distance a ray
must travel.
– Because angle of incidence determines path length, atmospheric
obstruction reinforces the pattern established by the varying angle of
incidence.
– Because they must pass through more atmosphere than high-angle
rays, low-angle rays are subject to more depletion through reflection,
scattering, and absorption.
• The pattern in the distribution of average insolation depends mainly on
latitude and amount on cloudiness.

16

Day Length
• Day Length—the longer the day, the more insolation
can be received and the more heat can be absorbed.
– Middle and high latitudes have pronounced seasonal variations
in day length, while tropical areas have little variation.

Latitudinal Radiation Balance
• Occurs because the belt of
maximum solar energy swings
back and forth through tropics
as the direct rays of sun shift
northward and southward in
course of a year.
– Low latitudes (about between
28° N and 33° S) receive an
energy surplus, with more
incoming than outgoing
radiation.
– There is an energy deficit in
latitudes north and south of
these low latitudes.
– This simple latitudinal pattern
is interrupted principally by
atmospheric obstruction.

Land and Water Contrasts
• Different kinds of surfaces
react differently to solar
energy, which plays a major
role in how Earth surface
affects the heating of the air
above it.
• There are almost limitless
kinds of surfaces on Earth,
both natural and human-made.
• Each varies in its receptivity to
insolation, which in turn affects
the temperature of overlying
air.

17

• Most significant
contrasts occur
between land and
water surfaces.
– Heating: generally, in
comparison to water,
land heats and cools
faster and to a greater
degree.

• There are four main reasons why water and land are
different:
1. Specific Heat—the amount of energy it takes to raise the
temperature of 1 gram of a substance by 1°C. Water’s specific
heat is about five times as great as that of land, so it takes
about five more times the energy to raise its temperature.
2. Transmission—water is a better transmitter than land (because
it’s transparent, while land is opaque). Heat diffuses over a
much greater volume (and deeper) in water and reaches
considerably lower maximum temperatures than on land.
3. Mobility—water’s mobility disperses heat both broadly and
deeply; on land, heat can be dispersed only by conduction, and
land is a very poor conductor.
4. Evaporative Cooling—water has more moisture, so more
potential for evaporation and losing heat; cooling effect of
evaporation slows down any heat buildup on water surface.

• Cooling—water surface
cools more slowly and to
a higher temperature as
compared to land for one
main reason:
– Heat in water is stored
deeply and brought only
slowly to surface.
– Circular pattern is created
so that entire body of water
must be cooled before the
surface temperature
decreases significantly.

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• Implications—oceans create more moderate climates for
maritime areas, so that interiors of continents hold the
hottest and coldest places on Earth.
– Distinction between continental and maritime climates is the
most important geographic relationship in study of atmosphere.
– Oceans provide a sort of global thermostatically controlled heat
source, moderating temperature extremes.
– Northern Hemisphere has greater extremes in average annual
temperature range because it is the land hemisphere—39% of
its area is land surface.
– Southern Hemisphere is water hemisphere—only 19% of its area
is land.

Mechanisms of Heat Transfer
• The tropics would become progressively warmer
(and less habitable) until the amount of heat
energy absorbed equaled the amount radiated
from Earth’s surface if not for two specific
mechanisms moving heat poleward in both
hemispheres:
– Atmospheric circulation—most important mechanism,
accomplishing 75 to 80 percent of all horizontal heat
transfer.
– Oceanic circulation—ocean currents reflect average
wind conditions over a period of several years.
– Ocean currents—various kinds of oceanic water
movements.

• Atmosphere and ocean serve as
thermal engines; their currents are
driven by the latitudinal imbalance
of heat.
• There is a direct relationship
between these two mechanisms:
• Air blowing over ocean is the
principal driving force of major
surface ocean currents;
• Heat energy stored by ocean
affects atmospheric circulation.
• The Basic Pattern—all Earth’s five
ocean basins are interconnected:
– North Pacific
– South Pacific
– North Atlantic
– South Atlantic
– South Indian

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• Basic Pattern
– Major Currents

• (Fig. 4-28)

• All the basins have a
single simple pattern of
surface currents:
– Basically, warm tropical
water flows poleward along
the western edge of each
ocean basin, and cool high-
latitude water flows
equatorward along the
eastern margin of each
basin.
• This pattern is impelled by
the wind and caused by
the Coriolis effect, the
deflective force of Earth’s
rotation.

• Northern and Southern Variations
– In Northern Hemisphere, the bulk of the current flow from North Pacific and North
Atlantic is prevented from entering the Arctic Ocean because continents are
close together.
– Flow is more limited in North Pacific because Asia and North America are very
close together.
– In Southern Hemisphere, distance between continents permits continuous flow
around the world.
– West wind drift—circumpolar flow around latitude 60° S.

20

Current Temperatures
• Low-latitude currents (Equatorial Current, Equatorial
Countercurrent) have warm water.
• Poleward-moving currents on the western sides of ocean
basins carry warm water toward higher latitudes.
• Northern components of the Northern Hemisphere gyres
carry warm water toward the north and east.
• Southern components of the Southern Hemisphere
gyres (generally combined into the West Wind Drift) are
strongly influenced by Antarctic waters and are
essentially cool.
• Equatorward-moving currents on the eastern sides of
ocean basins carry cool water toward the equator.

• Western Intensification
– The poleward moving warm currents off the east coast of
continents tend to be narrower, deeper, and faster than the
equatorward moving cool currents flowing off the west coast of
continents.
– This phenomenon is called western intensification because it
occurs on the western side of the subtropical gyres.
• Western intensification arises for a number of reasons.
– The Coriolis effect is greater factor.

• Rounding Out the Pattern
– The northwestern portions of Northern Hemisphere
ocean basins receive an influx of cool water from the
Arctic Ocean.
– Wherever an equatorward-flowing cool current pulls
away from a subtropical western coast, a pronounced
and persistent upwelling of cold water occurs.
– There is a deep ocean circulation pattern—
sometimes called the global conveyor belt
circulation—that influences global climate in subtle,
but nonetheless important ways.

21

Vertical Temperature Patterns
• Environmental Lapse
Rate
– Rate at which temperature
drops as altitude increases
can vary according to
season, time of day,
amount of cloud cover, and
other factors.
• Average Lapse Rate
– Average lapse rate—
normal vertical temperature
gradient, with temperature
dropping 3.6°F per 1,000
feet (6.5°C per kilometer).

Temperature Inversions
• Temperature inversions—
prominent exception to
average lapse rate, in
which temperature
increases with increasing
altitude.
– Common but usually brief
and only to a restricted
depth.
– Affect weather by cutting
possibility of precipitation
and creating stagnant air
conditions.

Temperature Inversions
• Surface Inversions—there are three kinds of surface inversions:
• Radiational inversions—surface inversion that results from rapid
radiational cooling of lower air, typically on cold winter nights (and
thus in high latitudes);
• Advectional inversions—surface inversion caused by a horizontal
inflow of colder air into an area (as in cool maritime air blowing onto
a coast); usually short-lived and shallow and can occur any time of
year, but are more common in winter than in summer;
• Cold-air-drainage inversions—surface inversion caused by cooler air
sliding down a slope into a valley; fairly common during winter in
some midlatitude regions.
• Upper-Air inversions
• AKA Subsidence inversions—temperature inversions that occur well
above Earth’s surface as a result of air sinking from above.

22

Global Temperature Patterns
• Maps of global temperature patterns display seasonal
extremes, not annual averages.
– January and July are chosen because, for most places on Earth,
they are the months with the lowest and highest temperatures.
– Temperature maps are based on monthly averages, which use
daily averages (not maximum daytime heating or maximum
nighttime cooling).
• Viewed correctly, they permit a broad understanding of Earth’s
temperature patterns.

– Fig. 4-32 – World Temperatures, July
– Fig. 4-33 – January

Prominent Controls of Temperature
• Four factors control gross patterns of
temperature—altitude, latitude, land-water
contrasts, and ocean currents:
– Altitude—most maps displaying world temperature
patterns adjust for altitude by reducing temperature to
what it would be if station giving temperature were at
sea level.
• Use average lapse rate to convert to sea-level temperature.
• Must realize that while these maps are useful for showing
world patterns, they do not indicate actual temperatures for
locations not at sea level.

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• Latitude—if Earth had uniform surface and
did not rotate, the isotherms would
probably coincide with parallels (with
temperature progressively decreasing
poleward from equator).
– Latitude is the primary governor of insolation,
the fundamental cause of temperature
variation over world.

• Land–water contrasts—continents have higher
summer temperatures than do oceans.
– Likewise, continents have lower winter temperatures
than do oceans.
• Ocean currents—because of land–water heating
contrasts, cool currents deflect isotherms
equatorward, whereas warm currents deflect
them poleward.
– Map shows how isotherms have a general east–west
trend, in conjunction with the influence of latitude,
which shows that temperatures tend to correspond
with latitude, with warmer temperatures toward the
equator and cooler temperatures toward the poles.

Seasonal Patterns
• Between summer and winter, there is a latitudinal shift of
isotherms, with them moving northward from January to
July and returning southward from July to January.
– This latitudinal shift is much more pronounced in high latitudes
than in low, and much more pronounced over continents than
over oceans.
– Temperature gradient, or the rate of temperature with horizontal
distance, is steeper in winter than in summer, and steeper over
continents than over oceans.
– Coldest places on Earth: landmasses in higher latitudes.
• In July, in Antarctica;

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Seasonal Patterns
• In January, in Subarctic portions of Siberia,
Canada, and Greenland.
– Hottest places on Earth: subtropical latitudes, where
clear skies do not give the protection that clouds give
in the tropics.
– In July, in northern Africa and southwestern portions
of Asia and North America;
– In January, subtropical parts of Australia, southern
Africa, and South America.
• Highest average annual temperatures: in equatorial regions,
because they do not have winter cooling.

Annual Temperature Range
• Maps showing average annual
temperature range, which is the difference
between the average temperatures of the
warmest and coldest months.
– Interiors of high-latitude continents and
continental areas in general have much
greater ranges than do equivalent oceanic
latitudes.
– Tropics have only slight average temperature
fluctuations.

Global Warming and the
Greenhouse Effect
• Air temperature increases when certain atmosphere gases (such as carbon
dioxide, methane, and nitrous oxide) inhibit the escape of longwave
terrestrial radiation. It is a naturally occurring process; without it, Earth
would be a frozen mass. Now, however, there are strong indications that
this effect has been intensified by human actions.
• According to data, the average global temperature has increased about
0.6°C during the 20th century, with the warmest records occurring since
1990s.
• Measurements of this temperature increase, both direct and proxy, have
pointed toward a clear warming trend on the Earth in recent decades.

Global Warming 101 NGC
http://www.youtube.com/watch?v=oJAbATJCugs&feature=fvw

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Greenhouse Effect
• Although the climate changes do
occur naturally, the evidence is
increasingly pointing to these
changes being caused by
anthropogenic sources.
• This increase in carbon dioxide is
attributed to the increased burning
of fossil fuels in recent decades.
• Carbon dioxide and other
“greenhouse gasses” appear to be
the principal offenders.
• Carbon dioxide is believed to be
responsible for about 64% of the
human-enhanced greenhouse
effect.
• Since 1750 carbon dioxide levels
have increased by more than
30%.

Greenhouse Effect
• The latest paleoclimatological
data indicate that the current
concentration of carbon
dioxide in the atmosphere of
380 ppm is greater than at any
time in the last 650,000 years.
• The current rate of increase is
greater than at any time in the
last 20 millennia.
• The increased use of other
gasses—methane,
chloroflurocarbons, and nitrous
oxides—have also contributed
to the increase in global
temperatures.

Greenhouse Effect
• These increases correlate with the
average increase in global temperature.
• The warming has not been globally
uniform, but rather widespread.
• Because of the complexity of feedback
loops in climate systems, predictions
regarding global warming are difficult to
formulate.

26

Greenhouse Effect
• Computer modeling shows that if the trend continues,
heat and drought would become more prevalent in much
of the midlatitudes, and milder temperatures would
prevail in the higher latitudes. Arid lands might receive
more rainfall. Ice caps would melt and global sea levels
would rise. Current living patterns would have to change
over much of the world.
• The International Panes on Climate Change (IPCC)
released a report in 2001 discussing climatic changes on
both global and local scales and the strong evidence
pointing to this change being a result of human activities.

Greenhouse Effect
• According to the IPCC report, it is estimated that
Earth’s climate system has changed on both a
global and regional scale since the pre-industrial
era and there is evidence that the warming
observed over the past 50 years is a result of
human activities.
• In early 2004 another IPCC report was released.
The findings reinforced the findings of the
previous report.
• The report can be found at (http://www.ipcc.ch).

27

Ch 4

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