Syllabus Edition

First teaching 2015

Last exams 2025

|

Positive & Negative Feedback

Alistair Marjot

Written by: Alistair Marjot

Reviewed by: Bridgette Barrett

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

8J408LfN_1-3-3-feedback-loop

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

1-3-3-negative-feedback-a
1-3-3-negative-feedback-b

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

1-3-3-positive-feedback-a
1-3-3-positive-feedback-b

Examples of positive feedback include melting of the ice caps and thawing of permafrost

Last updated:

Did this page help you?