The Global Heat Budget
There is a balance between incoming insolation and outgoing radiation within the
earth. This is known because the earth is neither warming up nor cooling down at an
extreme rate. There is a net gain in radiation on the earth’s surface except at the poles
which is affected by the albedo effect. There is a positive heat balance in the tropics
and a negative heat balance both at high latitudes and altitudes. There are two
transfers which occur to prevent tropical areas from overheating:
 Horizontal heat transfers - Heat is transferred away from the tropics by means
of wind movements and ocean currents
 Vertical heat transfers – This occurs through the processes of radiation,
conduction, convection and the transfer of latent heat.
Factors which affect insolation
The earth receives energy as incoming short wave solar radiation, this is also called
insolation. Factors affecting insolation can be separated in long term factors and short
term factors.
Long Term factors:
 Height above sea level – The atmosphere is not only warmed directly from the
sun, it is also warmed by heat radiated from the earth’s surface. As mountains
increase in height, the land mass decreases resulting in less heat being
transferred to the atmosphere. Also, as we increase altitude, the density of air
decreases thus decreasing its ability to hold heat.
 Altitudes of the sun – Places located at lower latitudes are exposed to higher
temperatures than those located at higher latitudes. Places located at higher
latitudes experience lower temperatures since energy is lost through
absorption, scattering and reflection more than those at lower latitudes. The
rays have a greater distance to travel and the thickness of the atmosphere is
greater in distance also.
 Land and sea – many factors influence the abilities of the land and see to
absorb and transfer energy. The ocean can absorb more energy to a depth of
10m; this is transferred further by the use of waves and currents within the
ocean. The ocean has a great specific heat capacity than the land as well. The
specific heat capacity of water is 1.0 while that of land is 0.5. ASSIGNMENT:
Why does the ocean heat up slower than the land in the summer, and why does
the land lose heat faster than the ocean in the winter? What is a thermal
reservoir?
 Prevailing winds – Wind temperate is mostly determined by the temperature of
the areas over which it blows.
 Ocean currents – Already mentioned in horizontal heat transfer, this is the
process whereby warm water carries heat towards the poles while cold
currents carry water towards the equator.
Short term factors:
 Seasonal changes
 Length of day and night – at the equator the days and night are more or less
equal but in Polar Regions there can be continuous darkness during parts of
winter or continuous sunlight during certain parts of summer.
Local factors which influence insolation
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Aspect – This local factor is related to hillsides. Hillsides alter the angle at
which the sun will hit the land. For example, many alpine valleys in
Switzerland and Austria have an east-west orientation meaning the valleys
face either north or south. South facing slopes will be warmer and drier than
north facing slopes.
Cloud cover – clouds reduce incoming and outgoing radiation. Thicker cloud
cover will limit the amount of heat coming in by the scattering of insolation,
absorption and reflection. This would also trap heat at night. So you have
cooler days and warmer nights. Light cloud cover results in warmer days and
cooler nights
Urbanisation – alters albedo.