Transcript Introduction - San Jose State University

MET 112 Global Climate Change - Lecture 9
Daisyworld
Eugene Cordero
San Jose State University
Outline
 Introduction
 Analysis
 Conclusions
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MET 112 Global Climate Change
A long time ago, in a galaxy far, far away...
…existed a land called Daisyworld.
Planet of same size, rotation, distance from the Sun as Earth
Sun of the same mass and luminosity as our sun,
Daisyworld is cloudless, no greenhouse gases, more land than ocean area.
Fertile, well watered soil, plants will grow anywhere if the temperature is right
Environment characterized by a single variable: temperature
2 daisy species, one with light colored flowers, one with dark colored flowers.
light = 0.7, dark = 0.2, bareground = 0.4.
All daisies are capable of reproducing.
Below 5oC, no daisies grow,
Over 40oC, all daisies die,
20oC is optimal for growth of all daisies.
Imagine that the sun of Daisyworld varies from
50% to 150% of present luminosity over geologic
time scales.
What would happen to daisyworld during this
change in solar luminosity?
Activity
Answer the following questions in groups of 2 (new partner
please!)
1. Plot out a graph of how you would expect the temperature of
daisyworld to change as solar luminosity increases from 0.5
to 1.5 (plot, 0.5, 0.6, 0.7, 0.8, …1.4, 1.5) without any daisies
on the planet.
2. Graph the temperature versus solar luminosity for daisyworld
with daisies (from computer program)
3. If it takes 1 billion years for the solar luminosity to increase by
0.1, then for how many years are the daisies alive on
daisyworld?
4. If daisies didn’t affect climate, then for how many years would
daisies be alive on daisyworld?
5. Explain how the daisies influenced the temperature. Hint:
Describe the relationship between the albedo, black daisies,
white daisies and the temperature.
6. Describe the feedback processes that occur during this
experiment. Hint: there may be more than one!
http://cs.clark.edu/~mac/physlets/DaisyW
orld/Daisy.htm?l1=0.75&aw=0.2&ab=0.2
A new theory of how the world works…
 In 1965, James Lovelock, a atmospheric chemist, was
thinking about why life evolved on earth and not on Mars or
Venus
 Why has temp of earth’s surface remained in narrow range
for last 3.6 billion years when heat of sun has increased by
25%?
 Also, why has oxygen remained near 21%?
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MET 112 Global Climate Change
Answers
 Difficult to understood without considering
role of life
 We understand that abiotic (non-living)
factors (physical, geological and chemical)
determine biological outcomes
 New idea is that Biotic (living) factors
feedback to control abiotic factors.
 Example:
Increased
Planetary
Temperature
Sparser Vegetation,
More Desertification
Increased
Planetary
Albedo
MET 112 Global Climate Change
Reduced
Temperature
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What kind of feedback is this
100%
Postive
Negative
Neither
Both
Sparser Vegetation,
More Desertification
Increased
Planetary
Albedo
MET 112 Global Climate Change
ot
h
er
ei
th
0%
N
N
eg
a
tiv
iv
e
Po
st
Increased
Planetary
Temperature
0%
e
0%
B
1.
2.
3.
4.
Reduced
Temperature
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Gaia Hypothesis
(proposed in
late 70’s)
Life collectively has a significant
effect on earth’s environment
Goes beyond
simple interactions
amongst biotic and
abiotic factors
Life optimizes the abiotic environment
to best meet biosphere’s needs
Atmosphere-Biosphere interactions are
Dominated by negative feedback
Evolution of life and Evolution of
its environment are intertwined
Biosphere can be modeled as a
single giant organism
A scientific twist of an ‘old idea’?
 The concept of ‘Mother Earth’ has been part of many
cultures.
 The ancient Greeks called their Earth goddess Ge or Gaia
 Lovelock defines Gaia
– "as a complex entity involving the Earth's biosphere,
atmosphere, oceans, and soil; the totality constituting a
feedback or cybernetic system which seeks an optimal
physical and chemical environment for life on this planet.“
 Through Gaia, the Earth sustains a kind of homeostasis (or
equilibrium)
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MET 112 Global Climate Change
Gaia Theory
 According to Dr. Lovelock
– “Gaia theory predicts that the climate and chemical
composition of the Earth are kept in homeostasis for
long periods until some internal contradiction or
external force causes a jump to a new stable state.”
 Lovelock’s Gaian Processes
– Oxygen levels
– Surface Temperatures
– Sea Salinity
– Carbon Burial
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MET 112 Global Climate Change
Gaia Theory
 Maintenance of Surface Temperatures
– According to Gaia, life regulates surface temperature
because it has remained within 10-20 C for over 3
billion years.
– It has also remained constant since life appeared.
– This is remarkable because the sun’s output has
increased by 30% or 40%.
 Maintenance of Oxygen Levels
– Gaia is responsible for maintaining the oxygen levels
within the range of oxygen-breathing animals.
– There has to be oxygen for ozone and that is when life
traveled to land.
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MET 112 Global Climate Change
Gaia
 Burial of Carbon
– “…a constant rain of carbonate bearing shells sinks
toward the ocean floor, where it ultimately forms beds
of chalk or limestone rock and thus prevents the
stagnation of carbon dioxide in the upper layers of the
sea…”
– “This process helps regulate the carbon dioxide
content of the atmosphere.”
– Carbon to silicate conversion process (negative
feedback process)
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MET 112 Global Climate Change
Daisyworld Experiments
 A simple mathematical model [Watson and
Lovelock (1983)]
 To demonstrate the principle of biological
homeostasis
– Automatic stabilization of a planet’s
temperature in the face of increased solar
luminosity through biological feedbacks
 Daisyworld supports the hypothesis of Gaia
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MET 112 Global Climate Change
How many years are the daisies alive on
daisyworld?
2 billion years
4 billion years
7 billion years
10 billion years
MET 112 Global Climate Change
ar
s
ar
s
ye
ye
io
n
bi
ll
10
7
bi
lli
o
n
ye
n
bi
lli
o
4
2
0 of 250
bi
lli
o
n
ye
ar
s
25% 25% 25% 25%
ar
s
1.
2.
3.
4.
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Activity Question 5: If daisies were not able to
influence climate, then for how many years
would daisies be alive on daisyworld?
2 billion years
4 billion years
8 billion years
12 billion years
100%
MET 112 Global Climate Change
ar
s
ar
s
0%
ye
ye
io
n
bi
ll
12
8
bi
lli
o
n
ye
n
bi
lli
o
4
bi
lli
o
n
ye
ar
s
0%
ar
s
0%
2
1.
2.
3.
4.
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Activity Question 7: Describe the feedback
processes that occur during this experiment.
Hint: there may be more than one!
100%
er
ei
th
N
N
eg
a
tiv
tiv
e
0%
ot
h
0%
e
0%
B
Positive
Negative
Neither
Both
Po
si
1.
2.
3.
4.
Results from Daisyworld:
– http://www.gingerbooth.com/courseware/daisy.html
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MET 112 Global Climate Change
– At the beginning of the simulation, Daisyworld is so cold that only a
few black daisies, and almost no white daises, can survive.
Whenever the planet's temperature decreases, the black flowers tend
to predominate, they absorb a little heat from the sun, which causes
the planet's temperature to rise, allowing a greater proliferation of
black daisies, more absorption of heat, and so on. As the planet
becomes hotter white daisies begin to breed as well, and eventually
the planet reaches a point of temperature equilibrium. Any increase in
temperature is combated by a greater proportion of white daisies; any
decrease leads to more black daisies. Such a system is remarkably
stable against varying solar input; the entire planet maintains
homeostasis. Eventually the external temperature becomes too hot
for the daisies to oppose, and heat overwhelms the planet.
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MET 112 Global Climate Change
Example
 Recall the faint sun paradox: Explanations
 Abiotic explanation:
– High greenhouse gases, less clouds, more ocean surface area
could have reduced global albedo on the early earth
 Biotic explanation:
– Dimethylsulfide (CH3-S-CH3) production by ocean
phytoplankton (DMS)
– causes aerosol formation, in turn reducing planetary albedo.
– When this led to too high global temperatures, phytoplankton
die off, thus providing a stabilizing, negative feedback on
planetary temperature.
 Ocean DMS production accounts for about ½ of total global sulfur
flux to the atmosphere
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MET 112 Global Climate Change
Without Daisies
Temperature
80 -
40 -
Daisies
5-
4 billion years
-20 Solar Luminosity
(Time)
With Daisies
Temperature
80 -
•
40 -
•
•
•
•
•
•••
Daisies
5-
•
•
7 billion years
-20 -
Solar Luminosity
(Time)
•
•