Daisyworld

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Daisyworld

• an introduction to systems

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Systems approach

• Systema group of interacting, interdependent or
  functionally interrelated elements forming a
  complex whole.
• Human physiology is an example of a complex
  system consisting of numerous components or
  sub-systems like the respiratory, cardiovascular,
  digestive, and nervous systems.
• In the case of human physiology, the state of the
  system is defined by a set of characteristic
  attributes like temperature, blood pH, O2 and
  nutrient levels, The components of a system
  interact by sensing each other (hormones). A
  change in the state of the system, or
  perturbation, is sensed by the components of the
  system, triggering a response by these components
  that will bring the state of the system back into
  equilibrium.

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Definitions

• A perturbation is a temporary disturbance of a
  system
• A forcing is a persistant disturbance of the
  system

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Systems Approach

• Components of a system are coupled together
  (wired) in such a way that information can flow
  between them. Couplings regulate the state of
  the system.

• Feedback is a self-perpetuating mechanism of
  change, and response to that change.
• Feedback loops link couplings together in a
  cause-and-effect pathway

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Feedback loops and system stability

• Negative feedback loops diminish the effect of a
  perturbation on a system, making systems stable
• Positive feedback loops amplify the effect of a
  perturbation on a system, making systems unstable

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Gaia Hypothesis

• James Lovelock and Lynn Margulis said that life
  itself has been responsible for maintaining the
  stability of Earths climate
• Earths climate is a self-regulating system in
  which the biota play an integral role
• This is not to say there is control by design,
  but that the Earths climate system is governed
  by natural biotic and abiotic negative feedbacks
  that regulate climate towards stability on
  different time-scales. What are these feedbacks
  and does the biota exert an essential controlling
  influence?
• This is not to say that the biota manipulate the
  climate for their own benefit, or optimize it to
  suit their particular growth requirements. We can
  think of many external forcings that the Earths
  biota have not been abe to overcome, and
  continued extinction of the Earth's biota is a
  driving force of biotic evolution.

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Daisyworld climate system
Albedoa measure of the reflectivity of a surface
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Couplings in Daisyworld climate systemresponse
of surface temperature to changes in daisy
coverage

• As daisy coverage increases the temperature
  decreases

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response of daisy coverage to surface temperature

• As temperature increases daisy coverage increases
  and then decreases
• The sign of the coupling between temperature and
  daisy coverage depends on the temperature

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Equilibrium states in Daisyworld climate system

• Q. How does the DW climate system respond to an
  external temperature forcing?
• A. It depends on the temperature of the planet

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Climate historyof Daisyworld
The response of Daisyworld to Increasing solar
luminosity
Too hot for daisies
Temperature increase attenuated by daisy growth
Daises begin growing