1. Systems and Feedback Loops

2. Questions for Today: What is a system and it’s parts? What are the different types of system response? What is a time delay? What is synergy and how is it harmful and beneficial?

3. Parts of a System A system is a set of components that function and interact in some regular way. Parts of a system –Inputs –Flows or thoroughputs –Outputs Environmental scienctists use computer modeling to analyze systems.

4. Fig. 2-10, p. 44 Heat Energy Inputs ThroughputsOutputs Energy resources Matter resources Information Economy Goods and services Waste and pollution

5. Feedback Loops Systems respond to change through the use of feedback loops Two types of feedback loops: –Positive – process that increases change –Negative - process that decreases change Homeostasis

6. Positive Feedback Loops A feedback loop occurs when an output of matter, energy, or information, is fed back into the system as an input and leads to changes in that system. A positive feedback loops causes a system to change further in the same direction. Examples of Harmful Feedback loops: –Deforestation –Melting of Polar Ice Caps Examples of Beneficial Feedback Loops: –Blood Clotting –Ecological Succession

7. Fig. 2-11, p. 45 Decreasing vegetation......which causes more vegetation to die....leads to erosion and nutrient loss...

8. Negative Feedback Loops Negative, or corrective, feedback loops causes a system to change in the opposite direction from which it is moving. Examples: –Thermostat –Recycling

9. Fig. 2-12, p. 45 House warms Furnace on Temperature reaches desired setting and furnace goes off Temperature drops below desired setting and furnace goes on House cools

10. Time Delays Time Delays are a gap in time between the input of a feedback stimulus and the response to it. The results of deforestation or pollutants usually have a time delay before the system reaches a threshold, or tipping point, where the damage is irreversible.

11. Synergy Synergy is when two or more process interact so that the combined effects are greater than the sum of their separate effects. Harmful Example: –Smoking and Asbestos leading to Lung Cancer –Air Pollutant Cocktails Beneficial Example: –Writing your Congressmen (Cheesy, Huh?)