Download Daisyworld - San Jose State University

A long time ago, in a galaxy far, far away...
MET 112 Global Climate Change - Lecture 12
…existed a land called Daisyworld.
ƒPlanet of same size, rotation, distance from the Sun as Earth
ƒSun of the same mass and luminosity as our sun,
ƒDaisyworld is cloudless, no greenhouse gases, more land than ocean area.
ƒFertile, well watered soil, plants will grow anywhere if the temperature is right
ƒEnvironment characterized by a single variable: temperature
Daisyworld
ƒ2 daisy species, one with light colored flowers, one with dark colored flowers.
ƒαlight = 0.7, αdark = 0.2, αbareground = 0.4.
ƒAll daisies are capable of reproducing.
ƒBelow 5oC, no daisies grow,
ƒOver 40oC, all daisies die,
ƒ20oC is optimal for growth of all daisies.
Eugene Cordero
San Jose State University, Spring 2004
Outline
ƒ Introduction
ƒ Analysis
ƒ Conclusions
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Activity 9
Imagine that the sun of Daisyworld varies from
60% to 150% of present luminosity over geologic
time scales.
Answer the following questions in groups of 2 or 3 (max).
1. Graph the temperature versus solar luminosity for daisyworld.
2. Explain how both temperature and albedo change on
Daisyworld as the solar luminosity increases from 0.5 to 1.5
(0.5, 0.7, 0.9, 1.1, 1,3, 1.5)
3. Describe the feedback processes that occur during this
experiment. Hint: there may be more than one!
What would happen to daisyworld during this
change in solar luminosity?
4. What conclusions might you come up with in regards to how
the daisies affected climate?
5. How could this idea also be applied to the climate of earth.
Explain?
Answers
A new theory of how the world works…
ƒ Difficult to understood without considering
role of life
ƒ We understand that abiotic (non-living)
factors (physical, geological and chemical)
determine biological outcomes
ƒ New idea is that Biotic (living) factors
feedback to control abiotic factors.
ƒ Example:
ƒ In 1965, James Lovelock, a atmospheric chemist, was
thinking about why life evolved on earth and not on Mars or
Venus
ƒ 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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Gaia Hypothesis
Gaia Hypothesis
(proposed in late
70’s)
Goes beyond
simple interactions
amongst biotic and
abiotic factors
Life collectively has a significant
effect on earth’s environment
ƒ Proposed by James Lovelock in mid 1960’s
ƒ States that the earth is ‘alive’ as a complex living
being.
ƒ Life and environment evolve as a single system.
Evolution of life and Evolution of
its environment are intertwined
ƒ
Biosphere can be modeled as a
single giant organism
MET 112 Global Climate Change
Gaia
A scientific twist of an ‘old idea’?
ƒ The concept of ‘Mother Earth’ has been part of many
cultures.
ƒ The ancient Greeks called their Earth goddess Ge or Gaia
ƒ
ƒ 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.”
ƒ 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."
ƒ Through Gaia, the Earth sustains a kind of homeostasis
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ƒ Lovelock’s Gaian Processes
–
–
–
–
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Gaia
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Gaia
ƒ Maintenance of Surface Temperatures
– According to Gaia, life regulates surface temperature
because it has remained within 10-20 C for over 3
billion years. (true?)
– It has also remained constant since life appeared.
This is remarkable because the sun’s output has
increased by 30% or 40%.
ƒ 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.”
ƒ Maintenance of Oxygen Levels
– Gaia is responsible for maintaining the oxygen levels
within the range of oxygen-breathing animals.
– The oxygen buildup began with the first appearances
of eukaryotic cells.
– There has to be oxygen for ozone and that is when life
traveled to land.
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Flavors of Gaia
Example
ƒ Two Gaia Models
– Soft Gaia hypothesis: There exists a coevolution of biological, physical and chemical
elements
– Hard Gaia hypothesis:
ƒ Recall the faint sun paradox: Explanations
ƒ Abiotic explanation:
– High greenhouse gases, less clouds, more ocean surface area
could have reduced global albedo on the early earth
ƒ Biotic explanation:
– Dimethylsulfide (CH3-S-CH3) production by ocean
phytoplankton (DMS)
–
– When this led to too high global temperatures, phytoplankton
die off, thus providing a stabilizing, negative feedback on
planetary temperature.
ƒ Ocean DMS production accounts for about ½ of total global sulfur
flux to the atmosphere
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Daisyworld Experiments
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Daisyworld Experiments
ƒ A simple mathematical model [Watson and Lovelock
(1983)]
ƒ To demonstrate the principle of biological homeostasis
– Automatic stabilization of a planet’s temperature in
the face of increased solar luminosity through
biological feedbacks
ƒ Coupled vegetation-climate model subject to external
perturbations
ƒ A simple mathematical model [Watson and Lovelock
(1983)]
ƒ To demonstrate the principle of biological homeostasis
– Automatic stabilization of a planet’s temperature in
the face of increased solar luminosity through
biological feedbacks
ƒ Coupled vegetation-climate model subject to external
perturbations
ƒ
ƒ Daisyworld supports the hypothesis of Gaia
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Daisyworld
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MET 112 Global Climate Change
States of equilibrium
ƒ Planet of gray colored surface with two types of plants –
black daisy and white daisy.
ƒ Barren surface and surface covered with black or white
daisies have different albedos.
ƒ By natural selection, the percentage of area covered
with black or white daisies varies.
ƒ This varies total albedo, thus affecting global
temperature.
ƒ The color of daisies indicates the amount of surface
reflection which, in turn, affects the Earth’s temperature.
ƒ When temperature is too cold, daisy seeds cannot
germinate.
ƒ When temperature is too hot, all daisies die.
ƒ The growth rates depend only on the local temperature.
ƒ Local temperature in part affected by local albedo
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– An equilibrium can be stable or unstable
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Stable
Unstable
Stable equilibrium
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