1. Introduction to Systems /Daisyworld
Chapter 2
Introduction to Systems
/Daisyworld

2. What is a System?
Definition: A system is a group of different components that interact with each other
Example: The climate system includes the atmosphere, oceans, polar caps, clouds, vegetation…and lots of other things

3. How do we study systems? Identify the components
Determine the nature of the
interactions between components

4. Systems Notation = system component = positive coupling
= negative coupling

5. Positive Coupling Atmospheric CO2 Greenhouse effect
An increase in atmospheric CO2 causes
a corresponding increase in the greenhouse
effect, and thus in Earth’s surface temperature
Conversely, a decrease in atmospheric CO2
causes a decrease in the greenhouse effect

6. Negative Coupling An increase in Earth’s albedo causes a
(reflectivity)
Earth’s
surface
temperature
An increase in Earth’s albedo causes a
corresponding decrease in the Earth’s surface
temperature by reflecting more sunlight back to
space
Or, a decrease in albedo causes an increase in
surface temperature

7. The interesting thing to do is to put
couplings together in feedback loops…

8. A Harmonious Family
childrens’
noise
parents’
anger

9. A Harmonious Family parents’ childrens’ anger noise positive coupling
negative coupling

10. A negative feedback loop:
A Harmonious Family
positive coupling
childrens’
noise
parents’
anger
negative coupling
street
noise
A negative feedback loop:
Stable system which resists change following a perturbation

11. NOT A Harmonious Family
positive coupling
childrens’
noise
parents’
anger
positive coupling
street
noise
A positive feedback loop:
Unstable system which changes further following a perturbation

12. The Non-Harmonious Family
Two possible states following perturbation:
1) Complete silence
2) Infinite noise
Positive feedback loops are unstable or not homeostatic.

13. The Harmonious Family
Noise levels return to near starting conditions following perturbation.
Negative feedback loops are stable or homeostatic.

14. Negative Feedback Loops:
Electric Blankets
person A’s
body
temperature
person A’s
blanket
temperature
person B’s
blanket
temperature
person B’s
body
temperature

15. A Positive Feedback Loop: Mixed-up Electric Blankets
person A’s
body
temperature
person A’s
blanket
temperature
person B’s
blanket
temperature
person B’s
body
temperature

16. A Positive Feedback Loop: Mixed-up Electric Blankets
Any perturbation will cause both people to adjust their blanket controls, but with undesired consequences.
Ultimately, one person will freeze (become infinitely cold) and the other person to swelter (become infinitely hot).

17. Conditions under which the system will remain indefinitely
Equilibrium State:
Conditions under which the system will remain indefinitely
--If left unperturbed

18. An Unstable Equilibrium State

19. An Unstable Equilibrium State
Perturbation

20. When pushed by a perturbation, an unstable equilibrium state shifts to a new, stable state.

21. A Stable Equilibrium State

22. A Stable Equilibrium State
Perturbation

23. When pushed by a perturbation, a stable equilibrium state, returns to (or near) the original state.

24. Daisy World

25. A simplified climate system:
Daisy World
Average Temperature = 30 oC
No clouds, no ocean
Soil = light gray (absorbs some light)
Life = white daisies (reflects all light)
Sun = like Earth’s
Daisy growth = changes with temperature

26. White Daisy Response to Increasing Solar Luminosity
Relative solar luminosity
The Earth System, Ch. 2

27. The rest of Chapter 2 will be done on the blackboard…