AS Level Geography: global Heat Budgets

1. TEMPERATURE & RADIATION BUDGET
Temperature and Altitude
�The graph shows the Environmental
Lapse Rate - the average global
temperature of air at altitude. It does not
represent rising or descending air.
�This graph would be different for any
place and at any time (it varies daily,
seasonally).
�Temperature tends to decrease with
altitude
�Air temperature changes fastest nearer
the earth’s surface (air warms and cools
mainly by contact with the earth)
�The troposphere contains most water
vapour and has the most variable
temperature, especially at low levels.
�Temperature inversions (when it
increases with altitude) occur where
various gases cause varying rates
absorption of radiation
�The tropopause is the lowest
permanent inversion; its height varies
from 8km at the poles to 16km at the
equator
Greenhouse
gases
ENVIRONMENTAL LAPSE RATE

2. SOLAR ENERGY - VARIATIONS� Solar energy is
transmitted to earth in
the form of short and
long wave (SW or UV,
and LW) radiation, since
the sun is very hot. It is
SW, UV radiation that is
absorbed effectively by
ozone. This is
insolation.
� Radiation may be
absorbed only by mass;
the more mass, the more
absorption.
� The earth also emits
radiation (all bodies at a
temperature above -
273°C do); this radiation
is almost entirely long
wave (LW) since it is
cooler than the sun. This
LW radiation is more
effectively absorbed by
greenhouse gases (CO2,
� The amount of
insolation emitted by
the sun varies with
sun spot activity.
This causes
fluctuations of up to
2% on a time scale of
decades, or more.
� The amount of
insolation reaching
the earth’s outer
atmosphere varies
with distance and
variations of the
earth’s orbit. This
causes fluctuations
of up to 4% on a time
scale of centuries or
more.
INSOLATION is the energy
which drives the
atmospheric weather
system. All winds, humidity
and weather systems are
driven by variations in
temperature.
Climate (long term variations
in the state of the
atmosphere) is related to
global and continental
location.
Weather (short term

3. Low sun (as sunset) shows more
red due to atmospheric dust and
pollution
GLOBAL VARIATIONS in INSOLATION
Insolation received at the earth’s
surface varies with latitude. The
higher angle of the sun in the sky
at the equator conveys more
energy per unit area than at
higher latitudes.� A given amount of radiation
covers a smaller area when
overhead than when at a low
angle; it is more concentrated
� Radiation
passes through a
greater length of
atmosphere when
at a low angle in
the sky than
when overhead.
Atmospheric
gases, dust and
vapour absorb
more energy
before it reaches
the earth’s
A high sun is more
effective than a
sun low in the sky

4. DAY LENGTH
Antarctic circle 66.5°S
Arctic circle 66.5°N
North Pole 90°N
South Pole 90°N
Equator 0°
Tropic of Cancer
23.5°N
Tropic of Capricorn
23.5°N
Six months daytime (March-Sept),
six months night (Sept - March)
Six months daytime (Sept - March),
six months night (March-Sept)
One day with 24 hours daylight
(June 21st); one day with 24
hours darkness (Dec 21st)
One day with 24 hours daylight
(March 21st); one day with 24
hours darkness (June 21st)
Sun is overhead once a year
(June 21st). Day length
always at least 10 hours.
Sun is overhead once a year
(Dec 21st). Day length always at
least 10 hours.
Constant day length - 12 hours
day and night all year round
Lengths of day and
night vay more
between the seasons
at higher latitudes.
This makes climate
more seasonal at the
poles than the equator
More
season
al
More
season
al

5. CONTINENTAL SCALE VARIATIONS
Satellite photo
taken in daytime
in June over
Scandinavia.
Warmer surfaces
show darker.
Note that land is
darker than sea
(ie land is
warmer).
Satellite photo
taken at night
over Britain in
January. Warm
surfaces show
darker. Note
that sea is
darker than the
land (ie sea is
warmer).
REASONS FOR CONTINENTAL
TEMPERATURE CONTRASTS
� Water has a higher specific heat than
land ie: it takes more energy to heat up
an equal mass of water by 1°C than it
does land. Water stores heat energy
more effectively than land.
� Insolation is concentrated into the top
few cm of the land, but is dispersed over
the surface 10-20m of water.
� Water loses energy through
evaporation and loss of latent heat.
� Turbulence causes warmer water to be
mixed with colder water, so temperatures
remain more constant.
� Reflectivity is NOT a cause.EFFECTS
� Temperatures of the sea vary less than on
land
� Land near the sea has temperatures
moderated
� The larger the ocean, the greater the effect
� Land temperatures vary more; the larger the
land mass, the larger the variation of
temperature.
� Continental scale land masses have a more

6. SMALL SCALE TEMPERATURE VARIATIONS
ALBEDO is the reflectivity of the earth’s surface. Darker
colours have a lower albedo; it absorbs more incident
radiation than lighter colours. On the photo, the snowcapped
mountains have the highest albedo, the forest the lowest. Ice
cover at the poles has a high albedo, further reducing
temperature. Water has a surprisingly low albedo, unless it
is calm and the sun is at a low angle. Albedo of vegetation
varies seasonally; albedo of earth varies with water content.
Cloud cover also increases albedo, and changes over time.
ASPECT is the angle from which
the sun shines. In Europe, south
facing slopes are warmer than
north facing. In the southern
hemisphere, the aspects are
reversed. On the photo above,
some snow remains on the north
facing slope; none on the south
facing slope. A south facing
ALTITUDE causes
temperature to decrease (by
about 0.6°C per 100m). Air is
warmed mainly by contact
with the ground, so air at
altitude is colder. It is also at
lower pressure ( less dense)
so absorbs insolation less
effectively. Hence
snowcapped peaks.
These small scale
factors vary over time.
Vegetation changes
daily and seasonally,
with growth and
human harvest.
Moisture content may
change the albedo.
Wind and sun angle
alter the albedo of
water.
Cloud cover also
affects reflectivity;
wind and rain affect
evaporation rates,
North facing
South facing

7. ENERGY CASCADE - DAY
DAYTIME insolation takes a variety of pathways. Incoming SW radiation is absorbed
by mass, hence more effectively by the earth’s surface than by the atmosphere whose
gases are much less dense.
The diagram represents a global average; the figures clearly vary with the angle of the
sun, day length, cloud cover, humidity, albedo, aspect and altitude. They vary from place
to place and over time (seasonally, diurnally and shorter time scales).

8. ENERGY CASCADE -NIGHT
NIGHT-TIME energy flows vary from those at daytime. Outgoing terrestrial radiation is
LW (the earth is colder than the sun) and continues over 24 hours. In the day, it is usually
less than the incoming solar radiation, so the earth warms up and soil heat flow is
downward. At night, it is clearly greater than insolation and soil heat flow is upward. Heat is
also transferred by evaporation and condensation, and by movement of warm or cold air or
water (sensible heat flow) in the form of winds and ocean currents. Again, this represents a

9. GLOBAL HEAT FLUX
� At 40°N and S, there is a balance of insolation
with outgoing LW radiation over the year.
� Insolation exceeds LW radiation in the daytime,
and in summer; the reverse is true at night and in
winter.
� Polewards of 40°N and S, there is an annual heat
deficit, despite periods of surplus during some
days and in summer.
� Equatorwards of 40°N and S, there is an annual
heat surplus despite periods of deficit at night and
in winter.
� Without movement of heat energy, the poles
would become steadily colder and colder, while the
equator would get progressively warmer. This
clearly does not happen.
� This heat transfer (flux) occurs by:� Ocean currents; cold polar water flows towards
the equator while warm water flows from equator
to pole.
� Winds which blow warm air to towards the poles
and cold to the equator.
� An excess of evaporation which takes up and
stores latent heat in water vapour, releasing it

10. OCEAN CURRENTS
Cold Sea temperature Warm
Labrador current
carries cold water from
equator to pole down
east coast of
N.America
Gulf Stream
carries warm
water from
equator towards
the pole, and
NW Europe
A similar anti-clockwise movement of
warm water polewards, and cold water
equatorwards can be seen in the Pacific.
Cold and warm winds blow in similar
fashion, though are not constrained to the
oceans!

11. HEAT TRANSFER by HUMIDITY
POLES - Precipitation exceeds
evaporation at high latitudes;
condensation releases latent heat
stored in water vapour.
EQUATOR -
Evaporation exceeds
condensation (and
precipitation); this
uses heat energy and
stores it in the form of
water vapour. Red
shows high humidity
from high rates of
LATENT HEAT is also
transferred from sea
to land in this way.
Evaporation exceeds
condensation over
oceans (which uses
heat); condensation
is greater over land,
which is heated up -
especially in winter.

12. The GREENHOUSE EFFECT, like a real greenhouse
(below) is to allow heat in, but not out. Gases in the
atmosphere (CO2, Methane) naturally trap outgoing LW
radiation more effectively than they do incoming SW
radiation. This retains heat, warming the earth’s
atmosphere.
GREENHOUSE EFFECT & OZONE
DEPLETION
Ozone traps UV
(SW) radiation from
reaching the earth’s
surface. Human
pollutants (CFCs
etc) are destroying
this protective layer
and causing
cancers of the skin
in Australia - near
the Antarctic hole in
the Ozone layer.
THE ANTARCTIC
HOLE IN THE
OZONE LAYER
This has, over
geological time, been
in balance. Now,
human activity is
increasing such gases
so the warming effect
is (possibly) beyond
recall. This is the