Introduction to Systems

1
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,
  vegetationand 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 Earths surface
  temperature
• Conversely, a decrease in atmospheric CO2
• causes a decrease in the greenhouse effect

6
Negative Coupling
Earths albedo (reflectivity)
Earths surface temperature

• An increase in Earths albedo causes a
• corresponding decrease in the Earths 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
parents anger
childrens noise
9
A Harmonious Family
positive coupling
parents anger
childrens noise
negative coupling
10
A Harmonious Family
positive coupling
parents anger
childrens noise
negative coupling
street noise
A negative feedback loop Stable system which
resists change following a perturbation
11
NOT A Harmonious Family
positive coupling
parents anger
childrens noise
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 As body temperature
person As blanket temperature
person Bs blanket temperature
person Bs body temperature
15
A Positive Feedback Loop Mixed-up Electric
Blankets
person As blanket temperature
person As body temperature
person Bs blanket temperature
person Bs 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
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 Earths
• 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