all we know, and all we can ever know, is a model. – dana ... · steve arquitt millennium...

Steve ArquittMillennium InstituteWashington D.C.

Systems Thinking &Causal Loop DiagramingRefresher

All we know, and all we can ever know, is a model. – Dana Meadows

The Challenge Is

Cartoon Bank

… To Avoid ...

…Unexpected Results!

Linear planning -> unintended consequences

• DDT• Introduced species • Antibiotic resistance• Chemical intense agriculture• Aral Sea disaster• Forest fire policy• And so on, Ad Infinitum!

“Open loop” thinking

Closing the loop

Goals

Decisions

State of theWorld

Sterman 2000

Unintended consequences ofOur decisions

Sterman 2000

We act only within a greater system

Sterman 2000

Systems Thinking (ST) / System Dynamics (SD)

Problem IDDynamic hypothesisCausal loop diagrams

Mathematical modelSimulation for hypothesis testing &Policy analyses

ST

SD

• FEEDBACK• TIME LAGS

• NON LINEAR• CLOSED BOUNDARY

The tools of Systems Thinking

Example Causal Loop Diagram CLD

Sterman 2000

Investment intourism

Seed investmentin tourism

+

Appeal ofdestination

Touristsarrivals

+

Money earnedfrom tourism

+

+

R

Crowding+

-

Environmentaldamage

+

-

B

B2

Tourisminfrastructure

+

+

CLD of tourism Development)

Price

ConsumptionInventorycoverage

Inventory

Production+

+

+

-

-

-

Meadows (1970)

Meadow's General CommodityCycle CLD

Anthropogenic Cemission rate

GHG+

Surface temp+

Ice cover-

Albedo+

-

Evaporationrate

+

Water vapour inatmosphere

+

+

R1

R2

Feedback loops in climate change

Benefits of CLDs

• Primary tool of Systems Thinking• Holistic and non-linear hypothesis• Exploratory• Low cost• Forum for discussion• Communication• Foundation for simulation model

(System Dynamics model)

Limitations of CLDs

• Conceptual only• Can easily become too cluttered• Doesn’t capture stock-flow

dynamics• Need experience to “see in loops”

Some principles of good practice

• Keep it simple!• “No problem – no systems model”• Focus on feedback loops• Avoid too much detail• All arrows uni-directional• Mark polarities (+ or -)• Mark feedback loops as R or B• Use expert opinion when available

https://vensim.com/vensim-personal-learning-edition/#vensim-ple

Vensim PLE software (used for the causal loop

sketches used in the training)is available free of charge at:

Software for ST & SD