1. Feedback Some examples to help understanding
David Redfern
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2. Introduction
This presentation supports the Geographical Ideas column explaining Feedback in Geography Review Vol. 30, No. 3. It provides some additional examples of feedback mechanisms in the geographical world to help you understand this key concept.
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3. Positive or negative feedback?
Positive and negative feedback either enhance or counter changes that occur within a system. ● Positive feedback enhances or amplifies change, moving a system away from its equilibrium state and making it more unstable. It creates a ‘snowball effect’. ● Negative feedback is an opposing force. It counters any change, lessening it and holding the system in a more stable equilibrium.
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4. The population, resources and pollution model
A number of feedback mechanisms can be seen in the population, resources and pollution (PRP) model, shown here.
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5. The population, resources and pollution model
The PRP model on the previous slide shows the ecological relationships that exist between population growth, human demand for and use of resources, and the environmental consequences of that demand/use. Positive feedback on the PRP model is shown by resource acquisition enhancing human survival and promoting population growth. For example, consider agriculture and population together. One drives the other with increasing intensity, so they can be viewed as being in a positive feedback spiral. Population growth has led to an increase in agricultural yields and production through technology, which in turn means that more population can be supported and so population growth continues. Here positive feedback can be said to produce ‘good’ outcomes.
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6. The population, resources and pollution model
However, positive feedback mechanisms may cause serious problems for people, such as the devastating cycles of depletion and environmental destruction. Eventually, in agricultural production, despite technological advances, soils are depleted, the carbon cycle is disrupted and yields diminish leading to instability in the natural landscape. Another problem is the use of fossil fuel energy, which has increased our capacity to produce and distribute food but is creating a rise in global temperature because of greenhouse gas emissions. The resulting shift in rainfall and drought patterns may devastate crop production in many areas. In both of these cases, positive feedback results in ‘bad’ outcomes.
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7. The population, resources and pollution model
Negative feedback loops also exist in the PRP model. Extreme resource use and pollution are of great concern. For example, continued soil erosion from overgrazing, over-cultivation or pollution of land and water courses could lead to a decline in food production that could have devastating effects on human population. This is already seen in parts of sub-Saharan Africa. Negative feedback from increased resource depletion could mean that people may have to expect a levelling out, or a decline, in their standard of living as fewer resources are available to them. Negative feedback could mean that there are insufficient resources for people and death rates will overtake birth rates, causing a population decline back to a stable of equilibrium.
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8. Carrying capacity
The negative feedback in the PRP model can be linked to the concept of carrying capacity, which is the maximum population size an area can sustain.
If the population of an area increases, the environmental damage created may cause a loss of food supply thereby reducing the population size.
If the population of an area decreases, the environmental benefits created may cause an increase in food supply thereby encouraging population growth.
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9. A coastal environment
This diagram shows negative feedback in a coastal scenario.
Consider a beach in a state of equilibrium when a storm removes material from it.
Negative feedback processes operate to restore the beach to its former state.
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10. Water and carbon cycles
Begin at ‘Start’ – how many positive feedbacks can you see?
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11. Water and carbon cycles
Three positive feedback loops are shown in the diagram on the previous slide.
The increased emissions of carbon dioxide warm the atmosphere:
the increased temperature results in higher evaporation rates from the warmer oceans and a wetter atmosphere, which leads to a positive feedback situation of further warming.
warmer oceans hold less carbon dioxide than colder waters, and hence more carbon dioxide is released, adding more greenhouses gases to the atmosphere
the increased temperature warms the tundra, which releases more carbon dioxide and methane (both greenhouse gases) which creates a further warming atmosphere.
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12. This resource is part of Geography Review, a magazine written for A-level students by subject experts. To subscribe to the full magazine go to:  
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