BAESI - Global Warming: Food Climate Connections
The Greenhouse Effect
Dr. Eugene Cordero
San Jose State University
Outline
 Greenhouse effect
 Energy Balance
 Activities
1
The Atmosphere
Principal Atmospheric Gases
GAS
MASS
Nitrogen
75%
Oxygen
23%
Argon
1%
Water Vapor
0.3%
CO2
0.06%
Principal Atmospheric Gases
GAS
MASS
Nitrogen
75%
Oxygen
23%
Argon
1%
Water Vapor
0.3%
CO2
0.06%
Greenhouse gases
Earth’s Energy Balance
 Energy entering top of atmosphere
= Energy leaving top of atmosphere
 Energy entering the Earth’s surface
= Energy leaving Earth’s surface
Solar Radiation (Sunlight)
 Sunlight is primarily made up of the
following:
– Visible Light (44%)
– Infrared Radiation (48%)
– Ultraviolet Radiation (7%)
Unit: 1 m =
0.000001 m
Energy from the Sun
 Obviously, the Sun provides the Earth with it’s energy. The
question is, how much of the Sun’s energy does the Earth get?
 Sun’s energy is either
– Scattered (reflected away) or
– Absorbed
 Scattering happens by bouncing off
– Particles in the atmosphere
– Earth’s surface
 Absorption happens when certain gases absorb the energy
– The reality is the only certain gases absorb certain
wavelengths.
Incoming solar radiation
 Each ‘beam’ of incoming sunlight can be either:
– Reflected back to space: Albedo
 Clouds
 Atmosphere
 Surface
– Or absorbed; either by atmosphere (e.g.
clouds or ozone) or Earth’s surface.
Absorption of radiation
 Absorption of shortwave radiation by atmospheric gas
molecules is fairly weak;
– most absorption of shortwave radiation occurs at the
Earth’s surface.
 Most gases do not interact strongly with longwave
radiation, however
– Greenhouse gas molecules absorb certain
wavelengths of longwave radiation.
Absorption of
radiation in the
Earth’s
atmosphere
Some surface
radiation
escapes to
space
Most
outgoing
longwave is
absorbed in
atmosphere
(by
greenhouse
gases)
Longwave radiation is
emitted from surface.
Some
atmospheric
radiation
escapes to space
Greenhouse
gases emit
longwave
upward and
downward
Some
atmospheric
radiation is
absorbed at the
surface
Greenhouse Effect
Sequence of steps:
1. Solar radiation absorbed by earth’s surface.
2. Earth gives off infrared radiation.
3. Greenhouse gases absorb some of the Earth’s
infrared radiation.
4. Greenhouse gases (water and CO2) give off
infrared radiation in all directions.
5. Earth absorbs downward directed infrared radiation
Result: warmer surface temperature
Earth’s Greenhouse Effect
 Without the greenhouse effect, the surface
temperature of Earth would be
– Very Cold (-18°C)
 Greenhouse gases play an important role in
shaping climate.
– More GHGs – warmer climate
– Less GHGs – cooler climate
Activity
Draw a diagram showing how the
earth is heated by the Sun.
Include arrows and/or lines to
indicate the ‘Energy Balance” of the
earth.
Energy Balance – Energy coming in
and energy going out.
In your diagram, include how clouds
absorb, reflect and emit energy.
Activity 2
1.
What percentage of the sun’s radiation is
a) absorbed by the Earth’s surface?
b) absorbed by the atmosphere
c) reflected out to space?
2.
What percentage of the energy received by the earth’s surface
comes directly from greenhouse gas emissions?
3.
If the sun’s radiation was to increase by 10%, how would the
following energy units change (increase, decrease or stay the
same)
a) Energy gained by the Earth’s surface.
b) Energy lost by the Earth’s surface.
c) Energy emitted by greenhouse gases.
d) Energy lost to space.