Summary Understanding and assessing Technologies for Sustainability
Lecture 1: Thinking in Systems – Donella H. Meadows (2008)
Chapter 1: The basics
System: An interconnected set of elements that is coherently organized in a way that achieves
something. It must consist of three kinds of things: elements, interconnections, and a function or
purpose.
Example of a system:
A football team is a system with elements such as players, coach, field and ball. Its interconnections
are the rules of the game, the coach’s strategy, the players’ communications, and the laws of physics
that govern the motions of ball and players. The purpose of the team is to win games. If you take
away football players, you quickly no longer have the same system.
How to know whether you are looking at a system:
Can you identify parts?;
Do the parts affect each other?;
Do the parts together produce an effect that is different from the effect of each part on its
own? ;
perhaps
Does the effect, the behaviour over time, persist in a variety of circumstances?
Elements: The elements of a system are often the easiest parts to notice, because
many of them are visible, tangible things. E.g. the elements of a system, a university, are students,
teachers, books but also school pride. Elements do not have to be physical things. Intangibles are
also elements of a system.
Interconnections: The signals that allow one part to respond to what is happening in another part.
E.g. In the university system, interconnections include the standards for admission, the requirements
for degrees, the examinations and grades etc. Some interconnections are physical flows, but many
interconnections are flows of information, signals that go to decision points or action points within a
system. These are harder to see.
Functions or purposes: Harder to see. A system’s function or purpose is not necessarily spoken,
written, or expressed explicitly, except through the operation of the system. The best way to deduce
the system’s purpose is to watch for a while to see how the system behaves. Purposes are deduced
from behaviour, not from rhetoric or stated goals. E.g. If a frog turns right and catches a fly, and then
turns left and catches a fly, and then turns around backward and catches a fly, the purpose of the
frog has to do not with turning left or right or backward but with catching flies.
Changing elements usually has the least effect on the system. If you change all the players on a
football team, it is still recognizably a football team.
If the interconnections change, the system may be changed dramatically. It may even become
unrecognizable. Change the rules from those of football to those of basketball, and you’ve got a
whole new ball game.
Changes in function or purpose also can be drastic. What if you keep the players and the rules but
change the purpose—from winning to losing.
Which is the most important part of the system? The elements, interconnections or function or
purpose?
All are essential. All interact. All have their roles. But the least obvious part of the system, its
function or purpose, is often the most crucial determinant of the system’s behaviour.
,Stock: The elements of the system that you can see, feel, count, or measure at any given time. A
system stock is: a store, a quantity, an accumulation of material or information that has built up over
time. Stocks change over time through the actions of a flow. A stock takes time to change, because
flows take time to flow. Stocks usually change slowly. They can act as delays, lags, buffers, ballast,
and sources of momentum in a system.
Example: Water in a reservoir behind a dam (stock) into which flow rain and river water, and out of
which flows evaporation as well as the water discharged through the dam.
Dynamic equilibrium: Its level does not change, although flow is continuously flowing through it
Several important principles that extend to more complicated systems:
Sum of all inflows exceeds the sum of all outflows; level of the stock will rise.
Sum of all outflows exceeds the sum of all inflows; the level of the stock will fall.
Sum of all outflows equals the sum of all inflows; the stock level will not change; will be held
in dynamic equilibrium
What is the role of stocks in the system?
The presence of stocks allows inflows and outflows to be independent of each other and
temporarily out of balance with each other.
It can be a source of stability.
Feedback loop: A closed chain of causal connections from a stock, through a set of decisions or
actions that are dependent on the level of the stock, and back again through a flow to change the
stock. E.g.
Two types of feedback loops:
Balancing feedback (B, stabilizing loops): The purpose of this
system is to keep your actual stock level near or at your desired
level. The feedback loop can correct an oversupply as well as an
undersupply. Balancing feedback loops are equilibrating or goal-
seeking structures in systems and are both sources of stability
and sources of resistance to change.
Reinforcing feedback (R, runaway loops): A virtuous circle that can cause healthy
growth or runaway destruction. Reinforcing feedback loops are self-enhancing,
leading to exponential growth or to runaway collapses over time. They are
found whenever a stock has the capacity to reinforce or reproduce itself.
, The time it takes for an exponentially growing stock to double in size, the “doubling time,”
equals approximately 70 divided by the growth rate (expressed as a percentage). If you put
$100 in the bank at 7% interest per year, you will double your money in 10 years (70 ÷ 7 =
10).
Chapter 2: A Brief Visit to the Systems Zoo
One Stock System:
A Stock with Two Competing Balancing Loops (Thermostat):
The information delivered by a feedback loop can only affect future behaviour; it can’t deliver a
signal fast enough to correct behaviour that drove the current feedback. There will always be a
delay in responding.
A Stock with One Reinforcing Loop and One Balancing Loop (Population and Industrial
Economy):
Shifting dominance: When one loop dominates another, it has a stronger impact on behaviour.
Because systems often have several competing feedback loops operating simultaneously, those
loops that dominate the system will determine the behaviour.
A System with Delays (Business Inventory):
Two Stock System:
A Renewable Stock Constrained by a Non-renewable Stock (Oil Economy):
, Renewable Stock Constrained by a Renewable Stock (Fishing Economy):
Non-renewable resources: Stock-limited. The entire stock is available at once, and can be extracted at
any rate (limited mainly by extraction capital). But since the stock is not renewed, the faster the
extraction rate, the shorter the lifetime of the resource.
Renewable resources: Flow limited. They can support extraction or harvest indefinitely, but only at a
finite flow rate equal to their regeneration rate. If they are extracted faster than they regenerate,
they may eventually be driven below a critical threshold and become, for all practical purposes, non-
renewable.
Three sets of possible behaviours of the renewable resource system:
Overshoot and adjustment to a sustainable equilibrium
Overshoot beyond that equilibrium followed by oscillation around it
Overshoot followed by collapse of the resource and the industry dependent on the resource
Chapter 7: Living in a World of Systems
Honouring information: Making the cleanest possible use we can of language. And, expanding our
language so we can talk about complexity.
The most general “systems wisdoms” from modelling complex systems:
Get the Beat of the System: Before you disturb the system in any way, watch how it behaves.
Expose Your Mental Models to the Light of Day: We have to put every assumption about the
system out where others (and we ourselves) can see them.
