IB Environmental systems and societies 1.2B Negative Feedback Loops Notes

Negative Feedback: How Systems Hold Themselves Steady

1. Feedback is any process in which the output of a system loops back to influence its own operation.
2. Negative feedback loops counteract change, keeping a system near stability and equilibrium.
3. They underpin homeostasis in living systems and equilibrium in ecological and planetary systems, preventing extreme swings that could threaten survival.

How Negative Feedback Works

1. A system starts in equilibrium, with inputs and outputs balanced.
2. A disturbance upsets the balance, for example a change in temperature, population size, or resource availability.
3. The system responds in a way that reduces or reverses the initial change, restoring stability.
4. As a result the system fluctuates around an average condition rather than drifting steadily away from it.

Predator-Prey Cycles: Feedback in Populations

Climate and Body Temperature: Feedback That Cools

Cloud Feedback in the Hydrological Cycle

1. Higher temperatures increase evaporation, which drives more cloud formation.
2. Clouds reflect incoming solar radiation because of their high albedo, which reduces heating.
3. As the planet cools, evaporation and cloud formation fall again, so the feedback holds temperature within narrow limits.

Temperature Regulation in the Human Body

1. Human homeostasis is a clear biological analogy for environmental feedback.
2. When body temperature rises, sweating and vasodilation cool the body.
3. When temperature drops, shivering and vasoconstriction raise heat production and retention.
4. These opposing responses hold body temperature near 37 degrees Celsius, a biological steady-state equilibrium.

Daisyworld: Life Regulating Planetary Temperature

1. Daisyworld was developed by James Lovelock and Andrew Watson as part of the Gaia hypothesis, which proposes that life helps regulate environmental conditions.
2. It is a computer simulation of a hypothetical planet orbiting a star whose luminosity slowly increases.
3. The model shows how life can stabilise planetary temperature through negative feedback.

How the Daisies Regulate Temperature

1. The planet is inhabited only by black daisies and white daisies.
   1. Black daisies have low albedo, absorb sunlight, and warm the planet.
   2. White daisies have high albedo, reflect sunlight, and cool the planet.
   3. Bare ground has an intermediate albedo.
2. The planet's temperature depends on the balance between absorbed sunlight and heat radiated to space.

Answering a Daisyworld Question

Equilibrium: The Balance Feedback Maintains

Why Equilibrium Matters

1. Equilibrium is crucial in ecosystems because it gives stability, resilience, and sustainability in the face of natural and human-induced change.
2. It lets systems keep working and maintain life-supporting conditions.

Steady-State Equilibrium

1. This is common in open natural systems such as ecosystems.
2. Inputs equal outputs over time, but small fluctuations occur around an average condition.
3. It is maintained by negative feedback loops that keep variables such as temperature, population, and nutrients within stable limits.

Stable Equilibrium

1. A system in stable equilibrium returns to its original state after a disturbance.
2. Small-scale disturbances, such as the death of a tree or a flood, trigger recovery mechanisms that restore balance.

Developing (Dynamic) Equilibrium

1. Some ecosystems pass through stages, forming temporary equilibriums during ecological succession.
2. As conditions change, the ecosystem shifts from one equilibrium state to the next until it reaches the climax community.

When Negative Feedback Breaks Down

1. Negative feedback keeps open systems from moving permanently away from equilibrium.
2. Fluctuations are normal and necessary, letting systems respond to change while avoiding collapse.
3. Systems that can no longer self-regulate, often under heavy human pressure, may lose equilibrium and shift to a new equilibrium.