The Radiation Budget and The Radiation Budget and the Greenhouse Effectthe Greenhouse Effect

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Incoming Solar RadiationIncoming Solar RadiationThe annual average of total incoming solar The annual average of total incoming solar

radiation is 342 Watts per square metre radiation is 342 Watts per square metre (W/m(W/m22).).

Incoming Solar RadiationIncoming Solar RadiationThis is called This is called insolationinsolation (the actual value (the actual value

for any region will depend on factors like for any region will depend on factors like latitude).latitude).

Incoming Solar RadiationIncoming Solar RadiationApproximately 30% of this is reflected back Approximately 30% of this is reflected back

by clouds, the atmosphere, and the by clouds, the atmosphere, and the surface.surface.

Incoming Solar RadiationIncoming Solar RadiationApproximately 30% of the remaining Approximately 30% of the remaining

radiation is absorbed by the atmosphere.radiation is absorbed by the atmosphere.

Incoming Solar RadiationIncoming Solar RadiationThe remainder is absorbed by and warms The remainder is absorbed by and warms

the surface . . .the surface . . .

Outgoing Thermal RadiationOutgoing Thermal Radiation. . . and is re-emitted as infrared radiation . . . and is re-emitted as infrared radiation

(and thermals and water vapour).(and thermals and water vapour).

Outgoing Thermal RadiationOutgoing Thermal RadiationThis infrared radiation can be re-absorbed This infrared radiation can be re-absorbed

by by greenhouse gasesgreenhouse gases in the atmosphere. in the atmosphere.

Greenhouse GasesGreenhouse Gases

This This natural greenhouse effectnatural greenhouse effect is a is a good thing because it helps maintain good thing because it helps maintain the Earth at a temperature to the Earth at a temperature to support life support life

(about 15(about 15ooC on average compared to C on average compared to about -20about -20ooC).C).

Outgoing Thermal RadiationOutgoing Thermal Radiation

Eventually, however, almost all the energy is Eventually, however, almost all the energy is radiated back into space as infrared radiated back into space as infrared radiation.radiation.

The Radiation BudgetThe Radiation Budget

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

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

Greenhouse GasesGreenhouse Gases

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

Greenhouse GasesGreenhouse Gases

Greenhouse gases include water Greenhouse gases include water vapour, nitrous oxide, methane, vapour, nitrous oxide, methane, ozone, CFCs (like freon), ozone, CFCs (like freon),

and . . .and . . .

Greenhouse GasesGreenhouse Gases. . . and the very influential carbon dioxide, . . . and the very influential carbon dioxide,

which has for most of human history been which has for most of human history been found at concentrations of approximately found at concentrations of approximately 280 ppmv (parts per million by volume) 280 ppmv (parts per million by volume) but which has climbed to over 388 ppmv but which has climbed to over 388 ppmv as of November 2010.as of November 2010.

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• The Greenhouse Effect GizmoThe Greenhouse Effect Gizmo

• p. 289 #1, 9, 4 p. 292 #4, 23p. 289 #1, 9, 4 p. 292 #4, 23