Energy Flows and Feedbacks – Quick Notes

System Dynamics

Studying systems helps scientists understand how matter and energy flow in the environment and how organisms relate to their surroundings.
Focus: system dynamics and changes across space and over time; track energy and matter flows.
Earth as a system: open for energy, essentially closed for matter due to gravity; energy enters as solar radiation and leaves as heat/reflectance, while most matter exchanges are internal or negligible at the planetary boundary.
\text{Earth: open for energy, closed for matter}.

Open system: exchanges of matter or energy across system boundaries occur.
Closed system: matter and energy exchanges do not occur across boundaries.
Most natural systems are open; some cave systems are nearly closed.
Mono Lake serves as a practical example: inputs (water, salts) and outputs (evaporation, biological removals) determine its dynamics; without outflow of water, salts accumulate.

Inputs: additions to a system (e.g., water, salts, energy).
Outputs: losses from a system (e.g., evaporation, sediment export).
Systems analysis: a method to determine inputs, outputs, and changes under different conditions.
Example (Mono Lake): quantify inputs (water, salts) and outputs (evaporation, brine shrimp removal by birds).
In some systems, some components (like salts in Mono Lake) may accumulate if there is no corresponding outflow.

Steady state: inputs equal outputs, so the system does not change over time.
Important for environmental science: helps assess whether resources or pollutants are increasing, decreasing, or stable.
Method: measure matter/energy within the system; if direct measurement isn’t possible, estimate storage and infer inputs/outputs.
Diagram example: a leaky bucket with equal inflow and outflow (
Input = Output
) implies no net change.
Real-world note: many natural systems (e.g., atmospheric water vapor balance, ocean-atmosphere water balance) have been in steady state, but changes (e.g., melting ice) can disrupt steady state.
Partial steady state: one part of a system can be steady while another part is not (e.g., Mono Lake was in steady state for water but not for salt before the LA Aqueduct).
Feedbacks help restore or disrupt steady state when inputs/outputs change.

Feedback: a process where changes feed back to alter the rate of that process.
Negative feedback loop: resists change; helps return to original state or reduce the rate of change.
Positive feedback loop: amplifies change; can push the system away from its starting point.
Common types:
- Negative example (Mono Lake): as water level drops, surface area shrinks, evaporation decreases, and the water volume tends to recover toward the previous level.
- Positive example (population growth): more births lead to more individuals capable of reproducing, accelerating population growth.
Note: 'positive' and 'negative' do not imply good/bad; they describe whether the feedback amplifies or dampens changes.
Climate context: feedbacks influence temperature regulation; negative feedbacks can damp warming, while positive feedbacks can amplify it.
Cloud feedbacks:
- Low-altitude clouds reflect sunlight, reducing warming (negative feedback).
- High-altitude clouds trap heat, increasing warming (positive feedback).
Health of environmental systems depends on proper functioning of feedbacks; breakdown of negative feedback can drive systems away from steady state.

Geographic variation: different conditions (temperature, precipitation, soil) create different communities across landscapes.
Example: Texas vegetation niches
- Sycamore trees in water-rich river valleys; pine trees on cold, dry mountain slopes.
Monitoring spatial differences helps predict responses to environmental changes (e.g., river drying affecting tree survival).

Earth's climate has undergone dramatic changes historically (e.g., Sahara’s transition from wetter to desert).
Small changes (orbital variations, climate cycles) can drive large ecosystem shifts over long timescales.
Ice ages, continental seas, and ancient fauna illustrate how natural systems respond via migrations, extinctions, and evolution.
Human activities have accelerated the pace and intensity of environmental changes, affecting system dynamics, feedbacks, and steady-state conditions.

Open vs closed systems; energy vs matter exchange.
Inputs, outputs, and systems analysis.
Steady state: inputs = outputs; changes indicate shifts in the system.
Feedbacks: negative (stabilizing) vs positive (amplifying).
Climate relevance: feedbacks influence temperature regulation and climate trajectories.
Variation across space and time drives differing ecosystem responses.
Historical context helps anticipate human-caused changes and their potential system-wide effects.