Download Greenhouse Effect: Earth and Venus

Units
MET 112 Global Climate Change - Lecture 2
“Greenhouse Effect: Earth
and Venus”
ƒ Our class will use both English and Metric unit
systems.
ƒ Most important:
– Distance (kilometres and miles)
– Temperature (ºC and ºF)
Dr. Eugene Cordero
San Jose State University, Spring 2004
Outline
ƒ Earth and Venus
ƒ Greenhouse effect
ƒ Climate Change
MET 112 Global Climate Change
1
ƒ 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
Unit Review
Three temperature scales:
•Kelvin
•Celsius
•Fahrenheit
ƒ What was today’s low temperature in ºC?
•What does temperature
mean physically?
ƒ California is about 800 miles long (from Oregon
to Mexico). How many kilometers is that?
ƒ 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?
MET 112 Global Climate Change
•What does 0° K mean?
3
Average Surface Temperature of Earth and
Venus: Factors to consider
Source of Energy:
The Sun
ƒ Which planet is closer to the Sun?
ƒ Which planet is more reflective?
ƒ Which planet has a larger ability to absorb and
retain solar energy?
MET 112 Global Climate Change
2
Sun radiates energy;
Energy “radiates
out” with distance
7
MET 112 Global Climate Change
8
Temperature Based Only on Distance to the
Sun
Earth and Venus
Venus
Based on solely the
position of Venus and
the Earth, which planet
would be warmer?
ƒ Based only on distance to the sun,
–
ƒ Average surface temperatures would be as
follows if the planets absorbed all of the
incoming sunlight:
–
–
ƒ However …
Earth
MET 112 Global Climate Change
9
Albedo
MET 112 Global Climate Change
11
Albedo
ƒ Albedo: The fraction of light reflected by
an object or a surface
ƒ White objects have ___________
ƒ Black objects have ___________
ƒ Venus and Earth do not absorb all of the
incoming sunlight
ƒ Part of the incoming sunlight is reflected back
into space
ƒ Earth reflects ______
ƒ Venus reflects ______
ƒ Which brings up a definition …
MET 112 Global Climate Change
13
Comparison of Earth and Venus
MET 112 Global Climate Change
15
Comparison of Earth and Venus
ƒ Earth’s albedo is ____
ƒ Venus’ albedo is ____
Earth absorbs __ % of the sunlight that strikes it.
Venus absorbs __ % of the sunlight that strikes it.
Venus
Let’s re-examine the surface temperatures with this
information.
Earth
Venus is completely covered by highly reflective
clouds; Earth is partially covered by clouds. Which
planet has a higher albedo? _______________
MET 112 Global Climate Change
17
MET 112 Global Climate Change
19
Absorption of Solar Radiation Taking into
Account Distance to Sun and Albedo
Temperature Taking Into Account Distance
to Sun and Albedo
ƒ Let intensity of sunlight striking Earth be denoted by
100
ƒ In these units, intensity of sunlight striking Venus is
193
Earth absorbs
units
Venus absorbs
units
ƒ If a planet’s mean surface temperature were
determined solely by the rate of absorption of
solar radiation,
– Venus would be ______ than Earth.
Thus, Earth absorbs sunlight at a greater
rate than Venus does. Amazing, but true!
MET 112 Global Climate Change
21
Actual Surface Temperatures
Recap
ƒ Based on average measurements combining
surface air temperature and sea surface
temperatures:
– Earth’s mean surface temperature is about
______
– Venus’ mean surface temperature is ______
ƒ
ƒ
ƒ
ƒ
ƒ Rate of absorption of sunlight can be calculated
from outer space; distance to sun and albedo
are all that are required
ƒ Surface temperature is not correctly predicted
from rate of absorption of sunlight
ƒ What could cause such a difference?
ƒ
So…
Venus absorbs less sunlight than Earth, yet
Venus’ surface is much hotter than Earth’s
Why?
MET 112 Global Climate Change
25
Earth
1.
2.
3.
4.
5.
ƒ
Nitrogen (N2)
Oxygen (O2)
Argon (Ar)
Water Vapor (H2O)
Carbon Dioxide
(CO2)
27
MET 112 Global Climate Change
Atmospheres of Earth and Venus (Gases)
ƒ
23
MET 112 Global Climate Change
Principal Atmospheric Gases
Venus
Earth
Venus
1. Carbon Dioxide
2. Nitrogen
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
MET 112 Global Climate Change
29
MET 112 Global Climate Change
30
Comparison of Atmospheres
Why is CO2 So Important?
Conclusions:
1.
ƒ Carbon Dioxide is a greenhouse gas.
ƒ Greenhouse gases are those gases that cause
the greenhouse effect.
ƒ The greenhouse effect makes a planet’s
surface temperature warmer than it would
otherwise be.
ƒ The stronger the greenhouse effect, the warmer
the surface (other factors being equal).
2.
3.
ƒ
MET 112 Global Climate Change
31
Greenhouse Gases
MET 112 Global Climate Change
33
Comparison of Greenhouse Effects
ƒ Water Vapor
ƒ Venus’ atmosphere contains ~ 25, 000 times as
much greenhouse gas as Earth’s!
ƒ So, Venus has a much stronger greenhouse
effect than Earth.
ƒ Thus, Venus has a much hotter surface than
Earth, despite the fact that Venus absorbs less
sunlight than Earth.
ƒ Carbon Dioxide
ƒ Methane (CH4)
ƒ Nitrous Oxide (N2O)
ƒ Ozone (O3)
ƒ CFC’s (chlorofluorocarbons)
MET 112 Global Climate Change
37
What does this have to do with climate?
ƒ Greenhouse gases like CO2 play an important
role in determining surface temperatures.
ƒ Changes in greenhouse gases, thus can
potentially increase or decrease surface
temperatures.
ƒ Therefore, the temperature of earth has more to
do with the Earth’s atmosphere than how close
the earth is to the sun.
MET 112 Global Climate Change
39
MET 112 Global Climate Change
38