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8/30 Feedback Loops

Last updated 7 months ago
11 questions
NEGATIVE FEEDBACK MECHANISMS – push a system back to its original equilibrium position
Example: Imagine you are out walking in the country. As you walk, the sun rises higher in the sky and the air temperature increases. Your body senses that your internal temperature is rising above 37°C and you start to sweat, which reduces your body temperature by evaporating water from your skin, returning your temperature to normal.
POSITIVE FEEDBACK MECHANISM – push a system to a new state of equilibrium
Example: Imagine you are lost on a high snowy mountain. When your body senses that it is cooling below 37°C, various mechanisms such as shivering help to raise your internal temperature again, but if these are insufficient to restore normal body temperature, your metabolic processes start to slow down, as, like most chemical reactions, they happen more slowly at lower temperatures. As a result, you become lethargic and sleepy and move around less and less, allowing your body to cool even further. Unless you are rescued at this point, your body will reach a new equilibrium – you will die of hypothermia.
Both natural and human systems are influenced by feedback mechanisms. Generally, we wish to preserve the environment in its original state, so negative feedback is usually helpful and positive feedback is usually undesirable. However, there are other situations where change is needed and positive feedback is advantageous.
Example: If students enjoy their Environmental Science lessons, they want to learn more, so attend classes regularly and complete assignments. Consequently, they move to a new equilibrium of being better educated about the environment.
There are a number of examples of how both positive and negative feedback mechanisms might operate in the physical environment. No one can be sure which of these effects is likely to be most influential, and consequently,we cannot know whether or not the Earth will manage to regulate its temperature, despite human interference with many natural processes.
Assignment:
1. Label each example as either positive or negative feedback and provide an explanation for your choice.
2. Draw diagrams of one example of positive feedback and one example of negative feedback using the examples given, to show how feedback affects a system. Include arrows to represent the feedback loops.
1

As carbon dioxide levels in the atmosphere rise:
• The temperature of Earth rises --> The rate of photosynthesis in plants increases --> More carbon dioxide is therefore removed from the atmosphere by plants, reducing the greenhouse effect and reducing global temperatures

1

Explaination:

1

As Earth warms:
• Ice cover melts, exposing soil or water --> Albedo decreases --> More energy is absorbed by Earth’s surface --> Global temperature rises --> More ice melts

1

Explaination:

1

As Earth warms, upper layers of permafrost melt, producing waterlogged soil above frozen ground:
• Methane gas is released in an anoxic environment --> Greenhouse effect is enhanced --> Earth warms, melting more permafrost

1

Explaination:

1

As Earth warms, evaporation increases:
• Snowfall at high latitudes increases --> Icecaps enlarge --> More energy is reflected by the increased albedo of ice cover --> Earth cools --> Rates of evaporation fall

1

Explaination:

1

What does albedo have to do with feedback loops?

1

Draw an example of a Positive Feedback loop diagram

1

Draw an example of a Negative Feedback loop diagram