Feedback Loops

Reinforcing Loops

Reinforcing loops amplify change in one direction, creating virtuous or vicious cycles that accelerate over time. They generate exponential patterns until external constraints eventually limit their growth.

Example: Word-of-Mouth Ticket Sales

When a theater production delights its audience, attendees tell friends who buy tickets and experience the same delight. Each new wave of satisfied customers becomes evangelists, creating a cascade of sales that fills increasingly larger venues.

Time-Series Pattern

The curve exhibits exponential growth—starting with a gentle slope, then accelerating rapidly in an ever-steepening climb as the compounding effect takes hold. The growth rate slows only when approaching market saturation, where it flattens into an S-curve's upper plateau due to limiting constraints.

Balancing Loops

Balancing loops sense deviation from a target and trigger corrective actions that push the system back toward equilibrium. They create stability when functioning properly, but generate oscillations when hampered by delays or constraints.

Example: Thermostat with Clogged Filter

A home heating system with a clogged air filter struggles to distribute warmth efficiently. The thermostat repeatedly triggers the furnace as temperatures fall below target, but the room heats unevenly, creating hot and cold cycles that never quite stabilize.

Time-Series Pattern

The line performs a damped wobble—swinging above and below the target value in decreasing arcs like a pendulum losing energy. Each oscillation becomes gentler than the last until the system finally settles into a steady state, the line straightening into a horizontal path.

Mixed Loops in the Wild

Real systems contain intertwined reinforcing and balancing loops that compete for dominance, creating complex dynamics. The behavior we observe emerges from this competition, often shifting dramatically when one loop overtakes another.

Example: Wetland Nutrient Cycles

A healthy wetland ecosystem maintains water quality through balancing feedback loops. When agricultural runoff introduces excess nutrients, microorganisms and plants increase their consumption rates in response, preventing algal blooms. The system naturally counteracts disruptions to maintain equilibrium until thresholds are exceeded.

Time-Series Pattern

The graph shows nutrient levels rising sharply after runoff events, followed by gradual declines as ecosystem processes absorb the excess. The pattern resembles a sawtooth wave with periodic spikes that return to baseline, demonstrating wetland ecosystem resilience until critical thresholds are exceeded, after which recovery becomes more difficult.

Check Your Understanding

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