2. Definition: A system is a group of different
components that interact with each other
Distinguish:
A system and its external environment.
A system is ….
Its external environment is …

3. 1. Isolated system no mass and energy exchange
2. Closed system no mass but energy exchange
3. Open system with mass and energy exchange

4. There is no actual isolated system in the world.
The universe can be considered as an isolated system
Mass constant
Energy constant
Toward  maximum disorder  die

5. Solar
Lon
g
rad -wave
iati
on
radiation
Earth System
Atmosphere
Ext
er n
fac al
tor
Ocean
Cryosphere
Biosphere

6. City

7.  Identify the components
 Determine the nature of the
interactions between components

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

9. 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

10. Negative Coupling
Earth’s albedo
(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

11. Coupling:
Component 1
Component 2
Positive
same direction of change
increase
increase
decrease
decrease
Negative
opposite direction of change
increase
O decrease
decrease
O increase

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

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

14. NOT A Harmonious Family
positive coupling
parents’
anger
childrens’
noise
positive coupling

15. The Harmonious/Non-Harmonious Family
Two possible states following perturbation:
1) Complete silence
2) Infinite noise
Positive feedback loop keeps a system unstable.
Negative feedback loop keeps a system stable.

16. A number of negative coupling
 odd → a negative feedback loop
=
even → a positive feedback loop

17. Negative Feedback Loops:
Electric Blankets
Lisa’s
body
temperature
Lisa’s
blanket
temperature
Mike’s
blanket
temperature
Mike’s
body
temperature

18. Lisa’s body
temperature
Lisa’s blanket
temperature
Mike’s blanket
temperature
Mike’s body
temperature

19. 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).

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

21. e
ble
bl
Sta ?
Sta ?
Stable?