Radiation Balance Applet
Data and Sources
From 4th edition envi. Chem. Text.
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Of the energy receive at the top of the earth’s atmosphere from the sun, over ½ is
IR and the most of the rest is visible light. A tiny bit of it is UV
Of the total incoming light,
o 50% is absorbed at the surface by
 Water bodies
 Soil
 Vegetation
 Human buildings, oth er human things, etc.
o 20% is absorbed by
 water droplet in the air
 clouds (water vapour)
 other molecular gases
 most of the UV component is absorbed by stratospheric
ozone/diatomic oxygen
 much of the IR is absorbe by Carbon dioxide and water
vapour
o the remaining 30% is reflected back into space by
 clouds (have an albedo of .4 to .8)
 suspended particles
 ice
 snow
 sand
 vegetation
 (overall these produce about a 0.3 albedo effect)
 (while ice and snow are particularly good reflectors, soil and
water are very poor reflectors- this has implicatios for the melting
of the arctic and the clear cutting of forests)
important things to consider- volcanic activity- without much volcanic activity,
the earth cools because of the fewrer aerosols in the air- while with increase
activity, the concentration of aerosols is much higher
the current temp increase is about .6’C.
The thermal infrared region is about 5 to 100 micrometers (energy in the form of
heat)
Outgoing IR (when absorbed by a greenhouse gas) is either re-emitted or
converted to heat)
o If it is re-emitted, the photon of IR goes in a completely randomized
direction
The planet is warmed up just as much by the indirect mechanism of reheating via
greenhouse gases, as by direct incoming radiation form the sun
o H20 naturally contributes to 2/3 of the greenhosu gas warming
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o Co2 naturally contributes to ¼ of the warming
Without these gg’s, the average earth temperature would be about -18’C rather
than +15’C.
Further evidence of this process is stratospheric cooling as global warming
occurs- see text for more detailed information
Each person in industrial country is responsible for on average 5 metric tons of
CO2 eath year from carbon containing fuels
Pos and neg feedback- one interesting neg feedback is an increased rate of
photosynthesis.
Taken form CHACR
Mars, 228 million km from the sun, with
an atmospheric mass less than 1% that of Earth’s, has an average surface temperature of - 47 °C.
Venus, 108 million km from the sun, with an atmospheric mass 90 times that of Earth’s has an
average surface temperature of 477°C.
taken by a scanning radiometer in space, help visualise two of the key components contributing to
earth’s radiation balance - the delicate balance between incoming energy from the sun and
energy radiated back into space that controls earth’s climate. A radiometer records energy from a
source, in this case the earth. The difference between the two images is the energy range in the
electromagnetic spectrum of the recorded radiation. The left sphere shows the amount of infrared
radiation (heat) emitted to space from the Earth's surface and atmosphere; the right sphere shows
the amount of sunlight reflected back to space by the ocean, land, ice, aerosols, and clouds. In
each case the amount of energy recorded by the radiometer is shown by a colour change.
Earth’s radiation balance is controlled by many variables, including the wavelength and intensity
of solar radiation; the tilt of the planet; the reflection of incoming solar radiation by the earth’s
surface and 12
atmospheric aerosols and clouds; the emission of radiation from the earth, and the absorption of
radiation by the earth’s surfaces and gases in the atmosphere.
Absorption of infrared radiation by ‘greenhouse’ gases
The image of the globe on the left in Fig 4.5 draws our attention to the loss of infrared or heat
energy from the earth’s surface, which cools our planet. What do the colours mean? The scale
shows the amount of infrared radiation emitted from the earth increasing from blue to red to
yellow. Remember that the peak of the radiation leaving earth’s surface is in the infrared region
of the spectrum, as shown in Fig 4.8. What is the effect on earth’s climate of the presence of
gases in our atmosphere that are able to absorb some of that infrared radiation? Recall from
Section 3.8 that the absorption of infrared radiation by a molecular substance causes molecular
vibrations - bonds stretch and twist. We use the term radiative forcing to describe the 15
change in the radiation balance of our climate system due to absorption of some of that infrared
radiation by naturally occurring or anthropogenic substances in our atmosphere. Besides water
vathe most important atmospheric gases causing radiative forcing are carbon compounds.
None of the three gases present in highest concentration, N2, O2 and Ar, are able to absorb
infrared radiation emitted by the earth. This is because of a condition that must be met for any
vibrating molecule to absorb infrared radiation - there must be a change in the relative positions
of the centres of positive and negative charge in the molecule during that vibration. This is
referred to as a change in the dipole moment of the molecule, and will be discussed further in
Chapter 6. For now it will be sufficient to know that this condition can not be met by argon,
nitrogen or oxygen, since the centres of positive and negative charge are always in the same place
in an isolated atom (Ar) or a molecule made of two identical atoms (N2 and O2). If a sample of
argon, nitrogen, or oxygen gas were placed in an infrared spectrometer, no absorption peaks
would be recorded
<MN>: The term ‘greenhouse’ gas can be misleading, since the mechanism for warming of our
atmosphere is completely different than that in a greenhouse. Greenhouses work mostly by
preventing loss of heat by convection.
Most of the trace carbon compounds in the atmosphere absorb heat energy emitted by the earth,
evident from strong absorption peaks in their infrared spectra. These gases are called
‘greenhouse’ gases because they are capable of absorbing some of the infrared radiation that
would otherwise escape into space and cool the planet. Most attention has focused on carbon
dioxide, since it is a product of all combustion reactions of hydrocarbons, and thus is inevitably
produced every time fossil fuels are burned.