Heating the Earth
Insolation, terrestrial radiation, convection,
conduction, radiation, albedo, aspect and
greenhouse effect
Geography 12 – Ms. Inden
How is the Earth heated
• Energy makes things move
• Radiation from the sun is energy
– Radiant energy moves in waves or rays
– The shorter the wavelength, the more energy
• Radiant energy can be reflected by or
absorbed by objects
– The atmosphere and the earth are absorbing and
also reflecting heat energy
• When the energy is absorbed, molecules in
objects to move, therefore creating heat
• Radiant energy powers the water cycle and
wind
Reflection or Absorption
• Radiant energy can be reflected by or
absorbed by objects
– The atmosphere and the earth are absorbing
and also reflecting heat energy
• When the energy is absorbed, molecules
in objects to move, therefore creating heat
• Radiant energy powers the water cycle
and wind
Conduction
http://www.qrg.northwestern.edu/projects/vss/docs/
thermal/1-how-does-heat-move.html
• Heat energy is transferred to matter (the atmosphere the
ocean, or the earth’s surface)
• The molecules and atoms in the matter start to move, and they
in turn bounce into other molecules, cause heat to move
through the object
• Important concept
for weather!
• Air pressure is the
weight of air
• The atmosphere
has areas of high
and low pressure
• Why?
– Gravity pulls air
down
– Weight of the
column of air
pushes down on
the lower air
What is Air
Pressure?
Convection
• Convection is when a substance that can flow (like water and
air), is heated IN THE PRESENCE OF GRAVITY
• It creates a cycle of rising and falling matter
• This moves heat energy around the ocean and the atmosphere
Why don’t the tropics get hotter and hotter, and
the poles colder and colder?
• Remember that the earth’s tilt on its axis (23.5
degrees) keeps the poles tipped away or toward
the sun during the sun and winter respectively
• This difference drives atmospheric circulation as
the heat moves from the surplus at the equator
to the deficit at the poles
–Air pressure is different in cold
and warm air masses and it
wants to equalize – from the
highs to the lows – more on this
later
• This movement also takes place
during night and day changes in
temperature
• It also occurs as temperature
differences exist over land and
water next to each other
• The scientific principle here is
convection – warm air rises,
cools, and falls back to earth
Insolation
• Remember
that
insolation is
solar
radiation
that is
received by
the earth’s
surface
http://pilotgcseradicalgeography.co.uk/2006/10/09/why-is-antarctica-cold/
Why doesn’t the earth just
keep getting hotter?
• Energy is absorbed, but it is also
reflected back into space
Short wave
Long Wave
http://mrsdlovesscience.com/greenhouse/greenhouse.html
http://greenerloudoun.wordpress.com/climate/
• 24% is absorbed by the atmosphere
• Clouds reflect about 23% (and absorb 3%)
• About 45% of incoming radiation reaches earth’s
surface
– 24% as direct
– 21% as diffuse radiation – this happens
because the radiation is first deflected by
molecules in the atmosphere and is
SCATTERED in all directions. Some of this
scattering reaches the earth’s surface
• Terrestrial (earth) radiation is when the earth
radiates the heat back out into the atmosphere
– Only 4% of this reaches outer space
Figures are variable (how thick is the cloud cover,
how much water vapour is in the atmosphere,
etc)
Follow the link to look at the
natural and human-made
greenhouse gases
• http://mrsdlovesscience.com/green
house/greenhouse.html
What is albedo
• A ratio that describes how reflective an
object is
• How much light is absorbed or reflected
by the surface
• Fresh snow has a high albedo
• Dark objects have a low albedo
• The earth has a wide variety of surfaces
that also change with the seasons or
human activity.
• Albedo matters to how much heat energy is
absorbed by the earth’s surface
– If the surface reflects heat, evaporation does
not occur, thereby impacting the formation of
cloud and precipitation
– In areas that have been deforested or overgrazed by cattle, the albedo becomes higher,
thereby causing a reduction of precipitation
and a greater likelihood of desertification
Take a look at the text
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Look at and draw the diagram on page 15.4 on page 246 that shows the
consequences for the natural environment of the fact that air cools as it
rises
Read on the same page about anomalies (something that is different than
you would expect) with regard to the fact that mountain tops are colder than
valley bottoms – this is called an inversion. Take note of what an inversion
is in your book.
The diagram on the next page – Fig. 15.6 is a good look at why the heat on
the earth’s surface and air pressure cause higher elevations to be cooler.
Copy this diagram into your notes.
It is important to understand the idea of microclimates (p. 252). Please note
that the textbook uses the term exposure for aspect. Aspect is which
compass direction a slope of a hill faces. Obviously, a slope that faces the
sun will be warmer than a slope that lies in the shade. If a valley is facing in
the direction of the prevailing winds will also be cooler because the wind will
blow away the heat radiating off the earth.
Urban microclimates – Take a few notes on heat islands (cities) – give
several important reasons why cities are hotter than the surrounding
country-side. What are some city planners doing to solve these problems?