Positive & Negative Feedback
- Most systems involve feedback loops
- These feedback mechanisms are what cause systems to react in response to disturbances
- Feedback loops allow systems to self-regulate
Changes to the processes in a system (disturbances) lead to changes in the system's outputs, which in turn affect the inputs
- There are two types of feedback loops:
- Negative feedback
- Positive feedback
Negative Feedback
- Negative feedback is any mechanism in a system that counteracts a change away from the equilibrium
- Negative feedback loops occur when the output of a process within a system inhibits or reverses that same process, in a way that brings the system back towards the average state
- In this way, negative feedback is stabilising - it counteracts deviation from the equilibrium
- Negative feedback loops stabilise systems
Examples of negative feedback include predator-prey relationships and parts of the hydrological cycle
Positive Feedback
- Positive feedback is any mechanism in a system that leads to additional and increased change away from the equilibrium
- Positive feedback loops occur when the output of a process within a system feeds back into the system, in a way that moves the system increasingly away from the average state
- In this way, positive feedback is destabilising - it amplifies deviation from the equilibrium and drives systems towards a tipping point where the state of the system suddenly shifts to a new equilibrium
- Positive feedback loops destabilise systems
Examples of positive feedback include melting of the ice caps and thawing of permafrost
