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 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 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

Growth limited by resources (food, nutrients) 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 An increase in atmospheric CO2 causes Greenhouse effect An increase in atmospheric CO2 causes a corresponding increase in the greenhouse effect, and thus in Earth’s surface temperature Conversely, a decrease in atmospheric CO2 causes a decrease in the greenhouse effect

Negative Coupling An increase in Earth’s albedo causes a (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

Conditions under which the system will remain indefinitely 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