Systems Theory Pedro Ribeiro de Andrade Gilberto Camara
Systems Theory Pedro Ribeiro de Andrade Gilberto Camara
How to model Natural-Society systems? Connect expertise from different fields Make the different conceptions explicit If (. . . ? ) then. . . Desforestation?
![“A hypothesis or theory [model] is clear, decisive, and positive, but it is believed](http://slidetodoc.com/presentation_image_h2/9042da06c7e87370bd024b514b5300c6/image-3.jpg "“A hypothesis or theory [model] is clear, decisive, and positive, but it is believed")
“A hypothesis or theory [model] is clear, decisive, and positive, but it is believed by no one but the man who created it. Experimental findings [observations], on the other hand, are messy, inexact things, which are believed by everyone except the man who did that work” Harlow Shapley (1885 -1972), American astronomer
![Models “[The] advantage of a mathematical statement is that it is so definite that](http://slidetodoc.com/presentation_image_h2/9042da06c7e87370bd024b514b5300c6/image-4.jpg "Models “[The] advantage of a mathematical statement is that it is so definite that")
Models “[The] advantage of a mathematical statement is that it is so definite that it might be definitely wrong…. . Some verbal statements have not this merit; they are so vague that they could hardly be wrong, and are correspondingly useless. ” Lewis Fry Richardson (1881 -1953) – first to apply mathematical methods to numerical weather prediction
What is a System? § Definition: A system is a group of different components that interact with each other § Example: The climate system includes the atmosphere, oceans, polar caps, clouds, vegetation…and lots of other things
How do we study systems? • Identify the components • Determine the nature of the interactions between components
Earth as a system
Growth and decay source: Ford, 1999
Growth and decay source: Ford, 1999
Limited growth Growth limited by resources (food, nutrients) source: Ford, 1999
Limited growth source: Ford, 1999
Systems Theory source: Meadows, 2008
Systems Theory: stocks and flows Stocks: measurable elements Flows: changes in stocks over time source: Meadows, 2008
Systems Theory: stocks and flows Multiple inflows and outflows source: Meadows, 2008
Systems Theory: stocks and flows Stock of trees and stock of lumber source: Meadows, 2008
Systems Theory: feedbacks Room temperature controlled by feedbacks from furnace and outside air source: Meadows, 2008
Shrimp farming
Simple model for shrimp farm
Results? Figure 7
Positive Coupling Atmospheric CO 2 Greenhouse effect • An increase in atmospheric CO 2 causes a corresponding increase in the greenhouse effect, and thus in Earth’s surface temperature • Conversely, a decrease in atmospheric CO 2 causes a decrease in the greenhouse effect
Negative Coupling Earth’s albedo (reflectivity) Earth’s surface temperature • An increase in Earth’s albedo causes a corresponding decrease in the Earth’s surface temperature by reflecting more sunlight back to space • Or, a decrease in albedo causes an increase in surface temperature
Equilibrium State: Conditions under which the system will remain indefinitely --If left unperturbed
An Unstable Equilibrium State
An Unstable Equilibrium State Perturbation
When pushed by a perturbation, an unstable equilibrium state shifts to a new, stable state.
A Stable Equilibrium State
A Stable Equilibrium State Perturbation
A Stable Equilibrium State Perturbation
Conclusions § Two ways to increase stocks § Stocks act as delays or buffers § Stocks allow inflows and outflows to be decoupled
- Slides: 31
