1.2C Positive feedback loops Notes

1. A positive feedback loop occurs when a disturbance amplifies itself, pushing a system further away from equilibrium rather than restoring balance.
2. This can cause rapid and sometimes irreversible changes in natural and human systems.

How Positive Feedback Loops Work

1. Positive feedback amplifies initial disturbances rather than counteracting them.
2. The system experiences self-reinforcing cycles, where outputs act to strengthen the original process.
3. Over time, these loops destabilize the system and may lead to a new equilibrium or even system collapse.
4. Unlike negative feedback, which stabilizes a system, positive feedback accelerates change in either direction (increase or decrease).

Key Characteristics

1. Destabilizing: drives systems away from equilibrium.
2. Amplifying: increases deviation from the initial state.
3. Nonlinear: changes accelerate over time rather than occur proportionally.
4. Common in human and natural systems such as climate processes, population dynamics, and resource depletion.

Melting Ice-Albedo Feedback (Climate System)

Process

1. Global temperatures rise due to greenhouse gas emissions.
2. Ice caps and glaciers melt, reducing surface reflectivity (albedo).
3. Less sunlight is reflected, and more solar radiation is absorbed by darker ocean or land surfaces.
4. Temperatures rise further, accelerating more ice melt.

Result

1. A self-reinforcing cycle of warming and melting that destabilizes the climate system.
2. Leads to positive feedback between energy absorption and temperature increase.

Long-Term Implication

1. The system moves away from its original equilibrium toward a new, warmer climate regime.
2. Melting Arctic sea ice contributes to sea-level rise, ocean circulation changes, and increased climate extremes.

Population Growth and Decline

Population Growth Feedback

1. As population increases, reproductive potential (number of breeding individuals) also increases.
2. This leads to more births, further increasing population size.
3. The larger the population, the faster it grows — an exponential growth loop.

Population Decline Feedback

1. As population decreases, fewer individuals are available to reproduce.
2. The reduced reproductive potential leads to further decline.
3. Eventually, this can push a species toward extinction, especially if genetic diversity drops below sustainable levels.

Permafrost Thaw and Methane Release

Process

1. Rising temperatures melt Arctic permafrost.
2. Melting releases methane (CH₄), a potent greenhouse gas.
3. Methane enhances the greenhouse effect, trapping more heat.
4. Warmer temperatures melt more permafrost, releasing more methane.

Outcome

1. This forms a runaway climate feedback loop, intensifying global warming.
2. The loop accelerates once initiated and is difficult to reverse.

Tipping Points and Regime Shifts

1. A tipping point occurs when a small change in one component of a system triggers a large-scale transformation, shifting the system into a new equilibrium or stable state.
2. These regime shifts can be difficult to reverse, leading to long-term consequences.

How Positive Feedback Loops Cause Tipping Points

1. Positive feedback loops amplify changes in a system, pushing it further away from equilibrium.
2. When these reinforcing cycles continue unchecked, they can drive the system past a critical threshold, leading to a tipping point, a sudden, often irreversible shift to a new stable state.

Steps in the Process

1. Small Change Occurs → A disturbance starts affecting the system.
2. Positive Feedback Reinforces Change → The initial disturbance triggers a chain reaction that accelerates itself.
3. Threshold is Crossed (Tipping Point) → The system can no longer return to its previous equilibrium.
4. New Equilibrium is Reached → The system settles into a new state, which may be less stable or less desirable.

Systems Near Tipping Points

1. Amazon rainforest: reduced rainfall and deforestation → decreased transpiration → more drying → potential shift to savanna ecosystem.
2. Coral reefs: slight increase in ocean temperature → bleaching → loss of symbiotic algae → more heat absorption → death of coral → new algal-dominated state.
3. Thermohaline circulation: freshwater influx from ice melt → reduced ocean salinity → disruption of deep-water formation → altered global climate patterns.