The Radiation Budget and the Greenhouse Effect

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					The Radiation Budget and the
     Greenhouse Effect
Incoming Solar Radiation
The annual average of total incoming solar
  radiation is 342 Watts per square metre (W/m2).
Incoming Solar Radiation
This is called insolation (the actual value for any
  region will depend on factors like latitude).
Incoming Solar Radiation
Approximately 30% of this is reflected back by
  clouds, the atmosphere, and the surface.
Incoming Solar Radiation
Approximately 30% of the remaining radiation is
  absorbed by the atmosphere.
Incoming Solar Radiation
The remainder is absorbed by and warms the
  surface . . .
Outgoing Thermal Radiation
. . . and is re-emitted as infrared radiation (and
   thermals and water vapour).
Outgoing Thermal Radiation
This infrared radiation can be re-absorbed by
  greenhouse gases in the atmosphere.
Greenhouse Gases

This natural greenhouse effect is a good
  thing because it helps maintain the Earth
  at a temperature to support life
(about 15oC on average compared to about
Outgoing Thermal Radiation
Eventually, however, almost all the energy is
  radiated back into space as infrared radiation.
The Radiation Budget

The net radiation budget, the difference
 between incoming radiation and outgoing
 radiation is therefore effectively zero.

Less than 1% of incoming solar energy is
  photosynthesized into chemical energy.
Greenhouse Gases

However, we are taking that extra less than
 1% that has been stored in the Earth (in
 the form of fossil fuels) and not only
 releasing its thermal energy but also
 excess greenhouse gases which absorb
 the outgoing radiation, putting our
 radiation budget out of balance.
Greenhouse Gases

Greenhouse gases include water vapour,
  nitrous oxide, methane, ozone, CFCs (like
and . . .
Greenhouse Gases
. . . and the very influential carbon dioxide, which
   has for most of human history been found at
   concentrations of approximately 280 ppmv
   (parts per million by volume) but which has
   climbed to over 388 ppmv as of November 2010.
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