1 University of Toronto Department of Computer Science © 2018 Steve Easterbrook. This presentation is available free for non-commercial use with attribution under a creative commons license. 1 CSC2720: Systems Thinking for Global Problems ➜ Last week: ÄWhy systems thinking? ÄWhat sort of discipline is it? ÄDefining a system ➜ This week: ÄFeedback Loops ÄThe idea of limits ÄMultiple feedback loops ÄCase Study: Feedbacks in the Climate System 1 University of Toronto Department of Computer Science © 2018 Steve Easterbrook. This presentation is available free for non-commercial use with attribution under a creative commons license. 2 Elements of a System 2 University of Toronto Department of Computer Science © 2018 Steve Easterbrook. This presentation is available free for non-commercial use with attribution under a creative commons license. 3 General Systems Theory ➜ How scientists understand the world: ÄReductionism - break a phenomena down into its constituent parts Ø E.g. reduce to a set of equations governing interactions ÄStatistics - measure average behaviour of a very large number of instances Ø E.g. gas pressure results from averaging random movements of zillions of atoms Ø Error tends to zero when the number of instances gets this large ➜ But sometimes neither of these work: ÄSystems that are too interconnected to be broken into parts ÄBehaviour that is not random enough for statistical analysis ➜ General systems theory ÄOriginally developed for biological systems: Ø E.g. to understand the human body, and the phenomena of ‘life’ ÄBasic ideas: Ø Treat inter-related phenomena as a system Ø Study the relationships between the pieces and the system as a whole Ø Don’t worry if we don’t (yet) fully understand each piece 3 University of Toronto Department of Computer Science © 2018 Steve Easterbrook. This presentation is available free for non-commercial use with attribution under a creative commons license. 4 Two approaches to study systems 1. Focus on the rules followed by individuals (bottom up) Ä Build simulations (agent models, physics models, etc) Ä Study the emergent behaviour 2. Focus on the patterns of behaviour of the system as a whole (top down) Ä Identify feedback loops, stocks, flows, etc Ä Build qualitative, causal models (eg system dynamics models) Ä Focus on holistic understanding (what-if questions), rather than quantifying behaviour 4
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University of Toronto Department of Computer Science
© 2018 Steve Easterbrook. This presentation is available free for non-commercial use with attribution under a creative commons license. 1
CSC2720: Systems Thinkingfor Global Problems
➜Last week:ÄWhy systems thinking?ÄWhat sort of discipline is it?ÄDefining a system
➜This week:ÄFeedback LoopsÄThe idea of limitsÄMultiple feedback loopsÄCase Study: Feedbacks in the Climate System
1
University of Toronto Department of Computer Science
© 2018 Steve Easterbrook. This presentation is available free for non-commercial use with attribution under a creative commons license. 2
Elements of a System
2
University of Toronto Department of Computer Science
© 2018 Steve Easterbrook. This presentation is available free for non-commercial use with attribution under a creative commons license. 3
General Systems Theory➜How scientists understand the world:
ÄReductionism - break a phenomena down into its constituent partsØ E.g. reduce to a set of equations governing interactions
ÄStatistics - measure average behaviour of a very large number of instancesØ E.g. gas pressure results from averaging random movements of zillions of atomsØ Error tends to zero when the number of instances gets this large
➜But sometimes neither of these work:ÄSystems that are too interconnected to be broken into partsÄBehaviour that is not random enough for statistical analysis
➜General systems theoryÄOriginally developed for biological systems:
Ø E.g. to understand the human body, and the phenomena of ‘life’
ÄBasic ideas:Ø Treat inter-related phenomena as a systemØ Study the relationships between the pieces and the system as a wholeØ Don’t worry if we don’t (yet) fully understand each piece
3
University of Toronto Department of Computer Science
© 2018 Steve Easterbrook. This presentation is available free for non-commercial use with attribution under a creative commons license. 4
Two approaches to study systems
1. Focus on the rules followed by individuals (bottom up)Ä Build simulations (agent models, physics models, etc)Ä Study the emergent behaviour
2. Focus on the patterns of behaviour of the system as a whole (top down)Ä Identify feedback loops, stocks, flows, etcÄ Build qualitative, causal models (eg system dynamics models)Ä Focus on holistic understanding (what-if questions), rather than quantifying
behaviour
4
2
University of Toronto Department of Computer Science
© 2018 Steve Easterbrook. This presentation is available free for non-commercial use with attribution under a creative commons license. 5
Behaviour of Complex Systems
Simple rulesMany relationships
Large numbersof interactions
Self-organizingbehaviour
ComplexNon-linearSystems
Feedback Loops
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University of Toronto Department of Computer Science
© 2018 Steve Easterbrook. This presentation is available free for non-commercial use with attribution under a creative commons license. 6
Feedback Loops
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© 2018 Steve Easterbrook. This presentation is available free for non-commercial use with attribution under a creative commons license.
Systems Activity:
Living Loops
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University of Toronto Department of Computer Science
© 2018 Steve Easterbrook. This presentation is available free for non-commercial use with attribution under a creative commons license. 8
Some Alternative Notations
BR
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University of Toronto Department of Computer Science
© 2018 Steve Easterbrook. This presentation is available free for non-commercial use with attribution under a creative commons license. 9
Example Stock’n’Flow Diagrams
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University of Toronto Department of Computer Science
© 2018 Steve Easterbrook. This presentation is available free for non-commercial use with attribution under a creative commons license. 10
Balancing Feedback Loops
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University of Toronto Department of Computer Science
© 2018 Steve Easterbrook. This presentation is available free for non-commercial use with attribution under a creative commons license. 11
Reinforcing Loops
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University of Toronto Department of Computer Science
© 2018 Steve Easterbrook. This presentation is available free for non-commercial use with attribution under a creative commons license. 12
House Thermostat
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University of Toronto Department of Computer Science
© 2018 Steve Easterbrook. This presentation is available free for non-commercial use with attribution under a creative commons license. 13
But the room doesn’t stay warm!
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University of Toronto Department of Computer Science
© 2018 Steve Easterbrook. This presentation is available free for non-commercial use with attribution under a creative commons license. 14
Multi-loop systems
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University of Toronto Department of Computer Science
© 2018 Steve Easterbrook. This presentation is available free for non-commercial use with attribution under a creative commons license. 15
Rational markets?
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University of Toronto Department of Computer Science
© 2018 Steve Easterbrook. This presentation is available free for non-commercial use with attribution under a creative commons license. 16
Substitutability
+
+
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© 2018 Steve Easterbrook. This presentation is available free for non-commercial use with attribution under a creative commons license.
Systems Activity:
Postcard Stories
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University of Toronto Department of Computer Science
© 2018 Steve Easterbrook. This presentation is available free for non-commercial use with attribution under a creative commons license. 18
Types of System➜ Natural Systems
Ä E.g. ecosystems, weather, water cycle, the human body, bee colony,…
Ä Usually treated as hard systems
➜ Abstract SystemsÄ E.g. set of mathematical equations,
computer programs,…Ä Interesting property: system and its
description are the same thing
➜ Symbol SystemsÄ E.g. languages, sets of icons, street signs,…Ä Soft because meanings change
➜ Designed SystemsÄ E.g. cars, planes, buildings, freeways,
telephones, the internet,…
➜ Human Activity SystemsÄ E.g. families, businesses, organizations,
markets, clubs, …Ä E.g. any designed system when we also
include its context of useØ Same for abstract and symbol systems!
➜ Information SystemsÄ Special case of designed systems
Ø Part of the design includes the representation of the current state of some human activity system
Ä E.g. MIS, banking systems, databases, …
➜ Control systemsÄ Special case of designed systems
Ø Designed to control some other system (usually another designed system)
Ä E.g. thermostats, autopilots, …
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© 2018 Steve Easterbrook. This presentation is available free for non-commercial use with attribution under a creative commons license.
Case Study:
The Climate as aSystem
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University of Toronto Department of Computer Science
© 2018 Steve Easterbrook. This presentation is available free for non-commercial use with attribution under a creative commons license. 21
Incoming shortwave
energyfrom the sun
Infra-redis radiated
in all directions
some sunlightIs reflected
Atmosphere(not to scale!)
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6
University of Toronto Department of Computer Science
© 2018 Steve Easterbrook. This presentation is available free for non-commercial use with attribution under a creative commons license. 22
Surface temperature of planet Earth(heat energy)
Heat from the sun
Infrared lost to space
B
Greenhouse Gases in the Atmosphere
Burning fossil fuels
Carbon capture
B
Reserves of fossil fuels
Carbon Sinks(forests,
oceans, soils)
Top-level stock and flow model
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University of Toronto Department of Computer Science
© 2018 Steve Easterbrook. This presentation is available free for non-commercial use with attribution under a creative commons license. 23
Surface temperature of planet Earth(heat energy)
Heat from the sun
Infrared lost to space
B
Greenhouse Gases in the Atmosphere
Burning fossil fuels
Carbon capture
B
Reserves of fossil fuels
Carbon Sinks(forests,
oceans, soils)
Places to intervene
3) Solar radiation management (giant space mirrors? Dust in stratosphere?) 2) Carbon Dioxide Removal
(re-forestation, biochar)
1) Transition to renewable fuels
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