Positive & Negative Feedback (DP IB Environmental Systems & Societies (ESS)): Revision Note

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