1. Systems Thinking and Climate Change
Unit 4 Lesson 1

2. Learning Goals Understand Basic Systems Principles Two Systems
Carbon Cycle as a System
Climate as a Systems
Sources, Sinks, Stocks and Flows
Feedbacks
Time Delays

3. Systems Concepts A system is a collection of things,
with a definable boundary,
that have some sort of relationship to each other.
Think of how system is used in everyday English (educational system, heating system…)

4. System Concepts: Stocks and Flows
Stock- part of a system that holds something.
Flow- is the movement of something between stocks in the system, or the movement of something in and out of the system.

5. A simple system: the bathtub
system boundaries: What is inside? What are we not including?

6. A simple system: the bathtub
First think about the system boundaries.
What is inside? What are we not including?
Then think about stocks.
In this case we have one stock. The tub holds water.

7. A simple system: the bathtub
System Boundaries
Stock
The tub holds water.
Flows
The faucet in
The drain out.

8. stocks are represented by boxes.
Representing a system
stocks are represented by boxes.
flows are represented by arrows.
So we can simplify our picture of the bathtub.
Flow out
Flow in
Stock

9. Flow can be sources or sinks
Representing a system
Flow can be sources or sinks
A source adds to the stock
A sink removes something from the stock.
In this case, what is being added, stored and removed is water.
Sink
Source
Stock

10. A more interesting system
What if we wanted to look at Lake Mendota instead of a bath tub?

11. Lake Mendota atmosphere evaporation precipitation River flow
River inflow
Lake Mendota
So why bother with all of this?
Well, we could use the model of the lake system to look at how much water is coming in and out of the lake. This could be helpful if we wanted to know about lake levels or flooding.
If we know how much is coming and and how much is going out should be able to figure out how the amount of water in the lake is changing. Is it rising? It it falling? Is it staying constant?
Change in stock
The difference between the amount coming in (source) and the amount going out (sink) is the net flow. (It is sometimes referred to as net flux)
Lets go back to the bath tub for a minute.
seepage to groundwater
groundwater inputs
groundwater

12. change in stock = sources - sink For the case of the bath tub, the
Net flow
change in stock = sources - sink
For the case of the bath tub, the
change in amount water in tub = ( water in ) - (water out)
If we know the sources and sinks, we can figure out how the amount of water in the tub will change.
This may seem pretty basic, but it can be very powerful, as we will see when we start to apply these concepts to atmostpheric CO2

13. What happens to the stock when…
Check Questions
What happens to the stock when…
1. source > sink?
2. source < sink?
3. source = sink?

14. What happens to the net flow in each case?
Check Questions
1. source > sink? stock increases!
2. source < sink? stock decreases!
3. source = sink? stock remains constant!
What happens to the net flow in each case?

15. Check Questions 1. source > sink? stock increases!
net flow is positive!
2. source < sink? stock decreases!
net flow is negative!
3. source = sink? stock remains constant!
net flow is zero!!

16. 2.2
2.9

17. Classwork: Global Carbon Cycle
Using the carbon cycle diagram, identify all the stocks. For each:
Quantify the stored carbon
List and quantify each in flow and outflow
Calculate the net flow
Label each stock as a source or a sink

18. Quantifying C - Units (1)
Stocks
Pg C [petagrams of carbon] or
Gt C [gigatonnes of carbon]
Flows
Pg C/yr [petagrams of carbon per year] or
Gt C/yr [gigatonnes of carbon per year]

20. Quantifying C - Units (2)
1 metric ton = 1,000 kg
1 metric ton = 2,205 lbs
1 (short) ton = 2,000 lbs
1015 g = 1 Pg = 1 Gt

21. Quantifying C Stocks and Flows
Storage (pG)
Flow in
(pG/yr) +
Flow out (pG/yr) -
Net Flow (pG/yr)
Source/Sink
Terrestrial Ecosystems
,500
120
2.9 60
2.2
0.7
Sink
Atmosphere
750
Ocean
Fossil Fuels

22. 2.2
2.9

23. Land Use Changes Sources Sinks Deforestation Plowing of prairies
Forest re-growth
(The missing sink)

24. North American Forests a C Sink

25. 2.2
2.9

26. Global Carbon Cycle- Key Points
Atmosphere and ocean serve as carbon sinks.
Major net sources are burning fossil fuels and land deforestation.
To reduce C in the atmosphere, the flow in must be smaller than the flow out.

27. Systems Dynamics: Feedback Loops and Delays
Topics we’ll cover:
Positive Feedback Loops
Negative Feedback Loops
Time Delays
Coupled Systems

28. Positive Feedback Loops
self-reinforcing
Change in one direction causes more in that direction
Example: Holding a microphone in front of a speaker.

29. Negative Feedback Loops
self-limiting or balancing
Change in one direction causes a corrective change in the other direction
Example: Thermostat in your house

30. Time Delays Time lag between a stimulus and a response
Example: Titanic steering

31. The Climate System (1)

32. The Climate System (2)
Global Climate System is coupled with Global Carbon Cycle

33. The Climate System (3) Positive Feedback Example:
Melting Ice Caps, Lower Albedo
Negative Feedback Example:
Cloud cover
Time Delay:
About 40 years

34. Radiative Forcing Mechanisms
Radiative forcing mechanism: a variable that impacts the global energy balance.
Examples: CO2 concentrations, sunspots, volcanoes.
Radiative forcing is measures in W/m2 [power/area].
Positive forcings increase trapped energy
Negative forcings decrease trapped energy

35. Fin

36. A more interesting system
Stop. Pull out a piece of paper and draw the stock and flows for water in this system.
Ask yourself. Where is the water stored? where is it coming from going to?
Think about the hydrological cycle.

37. seriously. stop and do it. it will help!
Lake Mendota
seriously. stop and do it. it will help!

38. Lake Mendota
essentially the lake is a big bathtub right? water comes in, water goes out.
But this is not very interesting. Lets see if we can be more specific.
Sink
Source
Lake Mendota

39. Department Store Example
Now we will go over the department store example from the pre-assessment. We’ll look at how we can apply systems concepts to the

40. 1. During which minute did the most people enter the store?

41. 2. During which minute was the net gain greatest?
Net gain is (source )- (sink). Where is this greatest?
approximately 28 people in - 8 people out = net gain of 20 people
minute 8.

42. 3. During which minute did the most people leave the store?

43. 4. During which minute was the net gain greatest?
You have to figure out when (source )- (sink) is most negative.
29 people in - 7 people out = net loss of 22 people
minute 17.

44. 5. During which minute were the most people in the store?
here is where systems thinking really helps. So far we know…
when sources > sinks, net flow is positive and therefore the stock is increasing. (in this case that means more people are coming in than going out so the number of people in the store MUST be increasing)
This is represented in yellow.

45. 5. During which minute were the most people in the store?
When sources < sinks, net flow is negative so the stock is decreasing. this means that on net people are leaving, so the stock of people in the store is getting smaller.
this is represented in green

46. 5. During which minute were the most people in the store?
When sources = sinks, we know that the net flow is zero. (this happened at about minute 13.)
So we know that until min 13, the number of people in the store had to be increasing, and after min 13 the number of people had to be decreasing.
Therefore, the most people were in the store at minute 13 and the least at minute 30.