Sustainability
Feedback Loops
Closed Systems
Easter Island’s Ecology Crash
The Role of IE in Sustainability
Goals for two days
Draw and analyze basic influence
diagrams – positive and negative
feedback. Delay. (Day 1)
 Understand the story of Easter Island’s
ecological crash as a positive feedback
loop in a closed system
 Understand principle of sustainability
 See why IE will help; links to more info;
ideas for projects

System Dynamics
Another descriptive model
 Gives qualitative predictions and
insights
 Software tools exist (STELLA) for
more quantitative predictions
 Industrial Dynamics, by Jay Forrester
(the classic reference)
 Popular book: The Fifth Discipline by
Peter Senge

Influence Diagrams:
Core Concepts
Cause and Effect thinking, Influence
or Causal Loop Diagrams
 Feedback
 Positive Feedback
 Negative Feedback
 Delay in Feedback Loops

Cause and Effect
Draw an arrow from cause to effect
 ``Influence’’ or ``affect’’ may be a
better term than “cause.”
 Examples

Practice
X
Skill at
X
Price of
Y
Sales of
Y
Population
Size
Number of
Offspring
Influence Diagrams
 Place
a “+” or a “-” at the arrow to
indicate the kind of influence
+ means: the more of one, the
more of the other (or less…less)
- means: the more of one, the
less of the other (or less…more)
Practice
X
+
Skill at
X
Price of
Y
-
Sales of
Y
Population
Size
+
Number of
Offspring
Feedback Loops
Any directed cycle is a feedback
loop
 The arrows must take you back to
where you started
 Feedback makes systems
complicated!
 Examples

+
Practice
X
Pleasure
from X
+
-
Price of
Y
-
Population
Size
Efficiency of
Y Production
+
Skill at
X
+
Sales of
Y
+
Number of
Offspring
Principle: the most important
causal influences are those that
are within feedback loops
Two Kinds of Feedback
POSITIVE
 Even # of - signs
 Amplifying
 Reinforcing
 Growth, but also
Decline
 Unstable

NEGATIVE
 Odd # of - signs
 Balancing
 Stabilizing
 Often good!
 Stable equilibria

Feedback Examples
A
pencil falls
 Standing on one foot
+
Imbalancing
Gravitational
Force
Tilt
+
+
+
Imbalancing
Gravitational
Force
Tilt
+
Muscular
Correction
-
+
+
Imbalancing
Gravitational
Force
Muscular
Correction
Tilt
+
+
Tilt
Detection
-
+
+
Imbalancing
Gravitational
Force
Muscular
Correction
Tilt
+
+
Tilt
Detection
-
Stock Price to
Earnings Ratio
Stock Price
+
+
Costs
A/C
Activity
Room
Temperature
-
+
+
Costs
+
External Heat
Analysis of an argument
or
How to make a
mountain out of a
molehill
+
A’s
anger
A’s
harshness
+
+
B’s
anger
B’s
harshness
+
Mountains out of
Molehills
 Whose
fault is it?
– “You started it”
 Cause,
effect, and blame are not
clear in complex systems
Delay
Taking a shower
 Carrying a cup of coffee
 Timing very important
 Beer game, supply chains
 Classic problem: when short-term
influence is of one type, and long-term
influence is of the other type

Floods
Drought
-
-
Local Food Production
Starvation
+
+
Delay
Population
Size
-
Feed
Hungry
+
Blood
Glucose
Level
Eat
Candy
+
Hunger
Level
-
+
Blood
Glucose
Level
Eat
Candy
+
Delay
+
Hunger
Level
-
Insulin
Production
45
40
35
30
25
20
15
10
5
0
Candy
Glucose
Insulin
More
Candy
Candy
Oscillations that
increase in
amplitude over time
are
a danger signal
Glucose and Insulin
 How
could
nature be so
stupid?
 How could
such an unfit
system
survive?
Nature isn’t stupid -We are!

1st appearance of
insulin regulation
– 10,000,00070,000,000 years
ago

1st appearance of
refined sugar
– 1500 to 2400 years
ago
Delay
Eat
Complex
Carbohydrates
Blood
Glucose
Level
+
Delay
+
Hunger
Level
+
-
Insulin
Production
Eat
Complex
Carbohydrates
Delay
+
+
+
Eat
+
Candy
Hunger
Level
-
+
Blood
Glucose
Level
+
Delay
-
Insulin
Production
Natural & Man-Made
Systems
合Natural systems have usually
›
evolved so that timings work well
Introduce a new element into a
smoothly running system and you
are lucky if timings remain good
› As change rate of technology  this
problem occurs more frequently
LIMITS TO GROWTH
+
Growing
Action
-
Slowing
Action
Condition
+
+
Startup grows
Wolf-free deer
population grows
Telcom Industry
–
–
Requires organization
Over grazes and dies
–
Overbuilt capacity
Tragedy of the Commons
+
Net Gains
for A
A’s
Activity
Total
Activity
B’s
Perceived Gain
per Activity
-
Gain per
Activity
+
Resource
Exhaustion
+
B’s
Activity
+
Delay
+
+
-
+
+
+
Net Gains
for B
Examples:
• England
• Whales
• H2O
Open Systems and
Closed Systems
Consider the earth…
What does Little’s Law
say about a closed
system?
A. Little’s Law does not apply to
systems with no throughput.
B. I = RT and R = 0 ) I = 0. Thus
eventually inventory drops to 0.
C. I = RT and R ! 0 ) T ! 1. Thus
inventory stays in the system forever.
Easter Island:
The Mystery
thanks to Carl Anderson for the beautiful photos
The Moral:
Positive (unbalancing)
feedback loops in a
closed system mean
disaster
Earth Island
Is the Earth suffering from the same
destructive patterns as Easter Island?
Frightening Facts


180 million tons of
trash/year in U.S.
50% of topsoil in U.S.
lost this century
– 25 billion tons/year
worldwide


Everglades extinct?
Loss of species
– frogs: 1/3 or more
– we save mountains, not
lowlands
“Every natural system
in the world today is in
decline”

Water, aquifers
– 20 billion gallon/year deficit in groundwater
– Ogalala Aquifer dry in 30-40 years at present
extraction rates




Fertility rates
Global Warming: North pole, Alaskan towns
Pesticides: 4.1 billion tons/year, 25 million
deaths
Equilibria: ozone, everglades, warming
Understanding Systems
Problems

Tragedy of Commons.
– Example: whales and the IWC
– Example: strip mining the ocean floor, where
there is a new species every square meter.

Limits to Growth
– Example: Human Population, now over
6,000,000,000

Transportation Engineering:
– Building more highways does not reduce traffic
problems. (Why?) It increases oil usage and
pollution.
Earth Island:
Solutions
Industrial Engineering
&
The Environment
Sustainability
The idea:
Could we continue our current activities
indefinitely?
“But really, this cannot go on indefinitely,
can it? Does anyone rationally think it
can?”
--Ray Anderson
Why IE & Sustainability?
IE is all about flow systems;
sustainability is all about balancing
flows.
 IE is all about cost-effectiveness. We
will never achieve perfect
sustainability. To make progress, we
must find the good bang-for-buck
ideas.

Assessing Systems



A production process can not always be
evaluated in isolation, but must be
evaluated in situ, as part of a system
IE methods and approaches can help in the
evaluation of systems
ECO-DESIGN by Ab Stevels (Professor at
Delft University and Senior Environmental
Advisor at Philips Consumer Electronics
Environmental Competence Centre)
Pollution Prevention
Idea: instead of treating waste,
don’t produce it.
– Move the environmental solution
upstream in the production process,just
as we move quality concerns upstream.
– Role of I.E.s
The Logistics of
Recycling and Take-Back
Transportation is usually a make-orbreak cost in recycle and take-back
 “Reverse Logistics” differs from
traditional supply-chain and distribution
logistics
 Take courses from Dr. Ammons
 Do a project

www.sustainable.gatech.e
du

ISTD: Institute for Sustainable
Technology and Development
– lectures and events
– listserv
– library
– recycling info
– primer on sustainability by Carol
Carmichael
Sustainability at
Georgia Tech
We are one of the leading institutions
 Georgia Tech mission statement:

– “…Georgia Tech seeks to create an
enriched, more prosperous, and
sustainable society for the citizens of
Georgia, the nation, and the world.”

Consider doing a sustainability project
for 4104. Example: water and sewer
costs will triple in Atlanta. That means
clients!
Policy Issues
Can we tax resource use rather than
profits?
 Companies and individuals don’t pay
the true cost for resources consumed
 Prisoner Dilemma and Tragedy of
commons tell us that the rules of the
game must be changed

Service vs. Product

Provide services, not goods
– Example: Ray Anderson’s company
Interfaces leases carpet squares

Imagine buying the use of a working
automobile for 12 years. Notice how
this would change the incentives of the
automobile manufacturer.
Goals for two days
Draw and analyze basic influence
diagrams – positive and negative
feedback.
 Understand the story of Easter Island’s
ecological crash as a positive feedback
loop in a closed system
 Understand principle of sustainability
 See why IE will help; links to more info;
ideas for projects
