Transcript Introduction - San Jose State University

MET 112 Global Climate Change - Lecture 2
“Greenhouse Effect: Earth
and Venus”
Dr. Eugene Cordero
San Jose State University
Outline
 Earth and Venus
 Greenhouse effect
 Climate Change
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MET 112 Global Climate Change
Units
 Our class will use both English and Metric unit
systems.
 Most important:
– Distance (kilometres and miles)
– Temperature (ºC and ºF)
 Conversions:
1.6 km = 1 mile; 1 km = 0.61 miles
(9/5 x ºC) + 32 = ºF
(ºF – 32) x 5/9 = ºC
MET 112 Global Climate Change
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Unit Review
 What was today’s low temperature in ºC?
 California is about 800 miles long (from Oregon
to Mexico). How many kilometers is that?
 If you were told that the average high
temperature in Sydney Australia at this time of
year is 26ºC, what temperature is that in ºF?
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MET 112 Global Climate Change
Three temperature scales:
•Kelvin
•Celsius °K= °C+273
•Fahrenheit
•What does temperature
mean physically?
•What does 0° K mean?
The Solar System
 “The nine planets”
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MET 112 Global Climate Change
Average Surface Temperature of Earth
and Venus: Factors to consider



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MET 112 Global Climate Change
Average Surface Temperature of Earth
and Venus: Factors to consider
 Which planet is closer to the Sun?
 Which planet is more reflective?
 Which planet has a larger ability to absorb and
retain solar energy?
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MET 112 Global Climate Change
Source of Energy:
The Sun
Sun radiates energy;
Energy “radiates
out” with distance
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MET 112 Global Climate Change
Earth and Venus
Venus
Earth
Based on solely the
position of Venus and
the Earth, which planet
would be warmer?
Sunlight striking
Venus is 93% stronger
than sunlight striking
Earth, thus we would
expect Venus to be
warmer
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MET 112 Global Climate Change
Temperature Based Only on Distance to
the Sun
 Based only on distance to the sun,
– Venus would be somewhat warmer than
Earth
 Average surface temperatures would be as
follows if the planets absorbed all of the
incoming sunlight:
– Earth: 5°C
– Venus: 55°C
 However …
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MET 112 Global Climate Change
 Venus and Earth do not absorb all of the
incoming sunlight
 Part of the incoming sunlight is reflected back
into space
 Earth reflects 30%
 Venus reflects 70%
 This leads to an important concept
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MET 112 Global Climate Change
Definition
 Albedo: The fraction of light reflected by
an object or a surface
 White objects have high albedos
 Black objects have low albedos
Increasing albedo
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MET 112 Global Climate Change
Comparison of Earth and Venus
Venus
Earth
Venus is completely covered by highly reflective
clouds; Earth is partially covered by clouds. Which
planet has a higher albedo? _______________
Venus
MET 112 Global Climate Change
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Comparison of Earth and Venus
 Earth’s albedo is 30%
 Venus’ albedo is 70%
Earth absorbs 70 % of the sunlight that strikes it.
Venus absorbs 30 % of the sunlight that strikes it.
Let’s re-examine the surface temperatures with this
information.
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MET 112 Global Climate Change
Absorption of Solar Radiation Taking
into Account Distance to Sun and
Albedo
 Let intensity of sunlight striking Earth be denoted by
100
 In these units, intensity of sunlight striking Venus is
193
Earth absorbs
100 x 0.70 = 70 units
Venus absorbs 193 x 0.30 =58 units
Thus, Earth absorbs sunlight at a greater
rate than Venus does!
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MET 112 Global Climate Change
Temperature Taking Into Account
Distance to Sun and Albedo
 If a planet’s mean surface temperature were
determined solely by the rate of absorption of
solar radiation,
– Venus would be colder than Earth.
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MET 112 Global Climate Change
Actual Surface Temperatures
 Based on average measurements combining
surface air temperature and sea surface
temperatures:
– Earth’s mean surface temperature is about
15°C
– Venus’ mean surface temperature is 480°C!




So…
Venus absorbs less sunlight than Earth, yet
Venus’ surface is much hotter than Earth’s
Why?
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MET 112 Global Climate Change
Recap
 Rate of absorption of sunlight can be calculated
from outer space; distance to sun and albedo
are all that are required
 Surface temperature is not correctly predicted
from rate of absorption of sunlight
 What could cause such a difference?
 The respective atmospheres of the Earth
and Venus
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MET 112 Global Climate Change
Atmospheres of Earth and Venus
(Gases)


Earth
1.
2.
3.
4.
5.
Nitrogen (N2)
Oxygen (O2)
Argon (Ar)
Water Vapor (H2O)
Carbon Dioxide
(CO2)
Venus
1. Carbon Dioxide
2. Nitrogen
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MET 112 Global Climate Change
Principal Atmospheric Gases
Venus
Earth
GAS
MASS
Nitrogen
3870 (75%)
Oxygen
1185 (23%)
Argon
67
(1%)
Water Vapor
17
(0.3%)
CO2
3
(0.06%)
TOTAL
5140
GAS
MASS
CO2
~500, 000 (96%)
N2
~20, 000
TOTAL
520, 000
(4%)
Compare the
amount of CO2
Unit: 1018 g
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MET 112 Global Climate Change
Comparison of Atmospheres
Conclusions:
1. Venus has a much more massive atmosphere
than Earth.
2. Venus’ atmosphere is mostly CO2.
3. The mass of CO2 in Venus’ atmosphere is
almost 100 times greater than the total mass
of Earth’s atmosphere.
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MET 112 Global Climate Change
Why is CO2 So Important?
 Carbon Dioxide is a greenhouse gas.
 Greenhouse gases are those gases that cause
the greenhouse effect.
 The greenhouse effect makes a planet’s
surface temperature warmer than it would
otherwise be.
 The stronger the greenhouse effect, the warmer
the surface (other factors being equal).
 Consider the blanket analogy
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MET 112 Global Climate Change
http://www.gardeners.com/sell.as
p?ProdGroupID=15871&DeptPGI
D=13596&lstCategory=0&lstSort=
&RecGroupNum=1
Greenhouse Gases
 Water Vapor
 Carbon Dioxide
 Methane (CH4)
 Nitrous Oxide (N2O)
 Ozone (O3)
 CFC’s (chlorofluorocarbons)
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MET 112 Global Climate Change
Comparison of Greenhouse Effects
 Venus’ atmosphere contains ~ 25, 000 times as
much greenhouse gas as Earth’s!
 So, Venus has a much stronger greenhouse
effect than Earth.
 Thus, Venus has a much hotter surface than
Earth, despite the fact that Venus absorbs less
sunlight than Earth.
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MET 112 Global Climate Change
What does this have to do with climate?
 Greenhouse gases like CO2 play an important
role in determining surface temperatures.
 Changes in greenhouse gases, thus can
potentially increase or decrease surface
temperatures.
 Therefore, the temperature of earth has more to
do with the Earth’s atmosphere than how close
the earth is to the sun.
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MET 112 Global Climate Change
Activity 1b
Answer each question and turn in at the beginning of the
next class
1. If the earth’s albedo was to increase due to more
clouds, how would the Earth’s temperature change?
2. Today, greenhouse gases like CO2 are increasing in
the atmosphere. How would that would change the
earth’s temperature?
3. If increases in greenhouse gases act to produce more
clouds, how would that change the earth’s
temperature (consider your answers to 1 and 2).
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MET 112 Global Climate Change