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New! Missouri Green Schools Program

Earth Quest: A game of Environmental Literacy

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Environmental Quizzes

K-2 biodiversity quiz

Coloring Sheets

channel catfish coloring sheet

Green Holidays Calendar

Modeling Environmental Problems

A short introduction to Models

A model is a simplified and abstract representation of a real-world object, event, process or phenomenon that can be used to understand cause and effect relationships, to make predictions about results, to generate interesting questions and to intervene to change outcomes.

An effective model makes accurate predictions about a real-world situation using a minimum number of elements and a minimum number of assumptions. The elements that are kept and the assumptions made will be different depending on what question the model is being used to answer.

Kinds of models and examples (these may overlap)

Modeling Environmental Problems

Systems models are very useful for identifying possible cause and effect relationships between human behaviors and environmental harm. Once a systems model can reliably predict the behavior of an environmental problem, it can be used to identify places where technology, education, economic policy or regulations could be used to stop the problem or reduce the harm.

Systems Modeling Basics

Stock stockThe size of the box can indidate the potential size of the stock and the height of the line across the width can indidate how full it is. However, the symbol used can be a circle, square, oval or and image of the actual stock.
Flow arrow the thickness of the arrow indicates the intensity of the flow

Sometimes, the same thing can be a stock or a flow. It depends on whether you are interested in its accumulation in a stock, its transfer between stocks, or both.

Simple System Model

diagram of a simple system model


Influence of one stock on another

Positive: if upstream stock goes UP, then downstream stock goes UP positive influence of an upstream stock  
Negative: if upstream stock goes UP, then downstream stock goes DOWN negative influence  


Relationship of stocks and flows

When stocks are large relative to flows, things can have a long residence time, large changes in flows are buffered and there may be little effect on downstream stocks and flows

stock large relative to flow

When stocks are small relative to flows, things can have a short residence time, even small changes in flows can cause large changes in stocks and large downstream effects

small stock relative to flow


Flow Pattterns

Flow patterns can be combined and modified to build systems models. There is no standard naming system for the kinds of patterns, but the descriptions below can help with understanding the kinds of flows that can be found.


Simple Direct Flow

simple direct flow


Bypass Flow
bypass flow


Branching Flow

branching flow


Confluent Flow

confluent flow


Network Flow

network flow


Feedback Flow or Feedback Loops

feedback flow


Building a Systems Model of an Environmental Problem

  1. PIck an ENVIRONMENTAL problem
    • The problem must involve some harm to living organisms, including people, and/or some harm to a critical ecological or biogeochemical process. Harm includes illness, reproductive failure, death, extinction, or loss of livelihood or home due to resource depletion, contamination or disaster.
    • The problem must be due to or partly due to human behaviors, actions or choices. Problems not caused by humans are major earthquakes, volcanic eruptions, tsunamis, or asteroid strikes. However, the harm these cause can be made worse by human choices, like where to site a nuclear power plant.
  2. RESEARCH the problem. Gather information from reliable sources about the harm, who is affected, how many are affected, and any cause and effect relationships. Look for numbers about the problem. Keep track of where you got each piece of information so you can go back to the source if you need to.
  3. Draw a diagram (first draft) to represent your system model. Put a stock (box) on the right to represent the harm. Then moving to the left put a stock to represent the most likely immediate cause of the problem and connect it to the harm stock with an arrow. Continue adding boxes using the flow pattern that fits what you know about the problem, connecting stocks with arrows as you go along.