Earth and the Greenhouse Effect
Learning Objectives
• At the end of this powerpoint presentation
students should be able to
– Describe how the atmosphere affects the Earth’s
temperature
– Describe the differences between climate change,
global warming, and the greenhouse effect
– GHG is an abbreviation for Greenhouse Gases
Earth’s Radiation and heat balance
• 343 W/m2 incoming solar radiation
– 214 W/m2 reflected back by clouds, surface,
atmosphere
– 67 W/m2 absorbed by atmosphere (and reflected
to surface)
Energy Balance: -6 C/21  F
Past Century the Earth’s Average
Temperature: 13.8 and 14.6 C (56.8
and
Thermal radiation
58.3 F)
Emitted by Earth
Radiation from sun
What gases are in the atmosphere?
Gases in Atmosphere
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Nitrogen Gas (N2)
Oxygen Gas (O2)
Argon Gas
Total
Oxygen percentage varies
• Water Vapor 0.5-4%
• Aerosols ???
• Other gases (0.01-0.04%)
78.09%
20.95%
0.93%
99.97
Radiatively Important Trace Species:
(also know as Greenhouse Gases (GHG)
•
•
•
•
•
•
Carbon Dioxide (CO2)
Methane (CH4)
Carbon Monoxide (CO)
Nitrogen Oxides (NOx)
Chloroflurocarbons (CFCs)
Ozone (O3)
Radiatively Important Trace Species
• Influence radiation balance or net heat
balance of the Earth
Energy Balance: -6 C/21  F
Past Century the Earth’s Average
Temperature: 13.8 and 14.6 C (56.8
and
Thermal radiation
58.3 F)
Emitted by Earth
Radiation from sun
Greenhouse Effect Rescues Us!
• O2 and N2 inert
• Water vapor, carbon dioxide, and other GHGs
adsorb thermal radiation
• Good absorbers are good emitters
How the Greenhouse Effect Works
• The evolution of atmosphere (and GHGs)
allows for a change in the energy balance
• Electromagnetic energy is absorbed by not
only the Earth’s surface, but also GHGs
• When energy is absorbed, the wavelength
emitted is different from the wavelength of
the incoming energy
• The wavelength change and GHG absorption
are key factors in the greenhouse effect
Solar radiation
in the form of lightwaves
passes through the
atmosphere
Most of this radiation
is absorbed by the
Earth and warms it
Some energy is radiated back
into space by the earth in
the form of infrared waves
Most of this radiation
is absorbed by the
Earth and warms it
Some energy is radiated back
into space by the earth in
the form of infrared waves
Most of this radiation
is absorbed by the
Earth and warms it
Some of this outgoing infrared
radiation is trapped by the
earth’s atmosphere and warms it
In summary: How a Greenhouse Works
Solar radiation
wavelength can
pass through
glass
Thermal radiation
emitted by plants,
soil, etc cannot pass
through
glass
How the Greenhouse Effect is Like an
Actual “Greenhouse”
Thermal radiation of earth absorbed by certain types of
gases in atmosphere. Can you guess which types of
gases these are?
GHG absorb different wavelengths
•
•
•
•
CH4 absorbs 7.3-8 μm
O3 absorbs 9.7-10.0 μm
CO2 absorbs 9.7-10.0 μm
H2O absorbs 16.9-24 μm
How the Greenhouse Effect is NOT Like an
Actual “Greenhouse”
• Convection processes in atmosphere cannot
be modeled in greenhouse
• Wind and other types of heat transfer are
included in air circulation patterns
Infrared Heat
• 83% of Earth’s thermal energy (far-infrared
energy) is absorbed
• This additional energy increases the Earth’s
average temperature
Greenhouse Effect vs. Enhanced
Greenhouse Effect
• Greenhouse effect is natural and keeps our
Earth at a habitable temperature
• Enhanced greenhouse effect is the average
global warming associated with anthropogenic
greenhouse gases (also referred to as Global
Warming)
• Climate change refers to both natural climate
change which occurs and sometimes is used in
place of the term enhanced greenhouse effect