Environmental Systems, Feedback & Risk · Grade 12 Science
Chapter: Conservation, Systems & Environmental DesignEnvironmental Systems, Feedback & Risk
Learning goals
- I can balance reservoir inputs, outputs, and storage change.
- I can distinguish feedback signs, hazards, exposure, and risk assumptions.
Readings for this unit
Before this unit
Budgets, percentages, ecosystems, and energy/resource decisions.
Use the detailed parent plan: two core 50–60-minute sessions per focused unit, with a third assigned for selected calculation/modeling topics. First study the core explanation and Parts 1–2 with their figures/checks; next study Parts 3–4, the whole-unit application, worked cases, varied practice and exit check. Attempt reasoning before opening guidance. Extend time when actual understanding requires it; investigations and chapter assessments have separate sessions.
Start with something to explain
Why can an average-risk score hide an important tradeoff?
Illustrative evidence case. Rare severe outcomes and frequent modest outcomes can have similar expected loss.
Notice and wonder
Record two observations using the stated quantities or relationships. Keep observations separate from possible causes. Write one question that a new measurement could help answer.
Why can an average-risk score hide an important tradeoff?
Your first model
Separate probability, consequence, exposure, vulnerability and uncertainty.
Build the language from the idea
- reservoir
- A stock of material or energy within a defined system.
- feedback
- An effect that returns to influence its own initiating process.
- exposure
- Contact between a hazard and people or ecosystems.
A systems model specifies reservoirs, flows, and boundaries. For a water budget, storage change=inputs−outputs. If precipitation adds 100 units while runoff and evaporation remove 80, storage rises 20. A missing flow can make a balance look inconsistent even when conservation holds.
A positive feedback amplifies a change; a negative feedback counteracts it. Positive does not mean beneficial and negative does not mean harmful. Ice loss reducing reflectivity can amplify warming; a control that reduces input as storage rises can stabilize a reservoir.
Residence time can be approximated as reservoir amount divided by throughput under a steady-flow model. A 1000unit reservoir with 100 units/year outflow has nominal residence time 10 years. Mixing, changing flows, and multiple pathways can make actual transit times heterogeneous.
Risk combines a hazard with likelihood, exposure, and consequences. An event of low probability can still merit attention when consequences are severe. Expected loss = probability×loss is a useful simplified decision metric, but it does not capture every distributional, ethical, or irreversible consequence.
Engineering choices compare criteria and constraints: treatment effectiveness, energy demand, cost, land, maintenance, and who bears burdens. A weighting table makes priorities explicit but does not turn value choices into physical facts. Test how a conclusion changes with plausible uncertainties or different priorities.
Environmental justice asks how risks and benefits are distributed and whether affected people participate in decisions. A sound proposal identifies stakeholders, documents evidence, and plans monitoring so unintended effects can be discovered and corrected. Uncertainty should guide better measurement and robust choices.
Build your understanding
Use the detailed parent plan: two core 50–60-minute sessions per focused unit, with a third assigned for selected calculation/modeling topics. First study the core explanation and Parts 1–2 with their figures/checks; next study Parts 3–4, the whole-unit application, worked cases, varied practice and exit check. Attempt reasoning before opening guidance. Extend time when actual understanding requires it; investigations and chapter assessments have separate sessions.
Part 1 · Use causal links with a stated boundary
A system is a selected set of interacting components within a boundary. Stocks are accumulated amounts; flows change them per time. A causal link indicates how one variable affects another under stated conditions and need not represent transferred matter. Label link type and units, retain relevant delays and external drivers, and explain why the boundary is appropriate. A diagram’s omission is a modeling choice that can limit predictions.
Read the visual model
Identify the labeled structures and units, then trace the arrows or compare values under the caption’s stated conditions. Separate the displayed evidence from a further inference. Write your reasoning before opening the guidance.
Is an arrow from temperature to respiration necessarily a material flow?
Visual reasoning — after your attempt
No. It can be a causal influence; material and energy accounts need their own quantitative flows.
A systems diagram names variables and directional effects within a selected boundary. A positive link means an increase in one tends to increase the other under the model; it does not mean good. A negative link means an inverse response. Links need mechanisms and conditions rather than correlation alone.
A rainfall-to-runoff link can be positive while a vegetation-to-runoff link depends on soil and event conditions. Define the relationship being modeled.
Pause and explain
What makes a link more than a decorative arrow?
Check your reasoning after answering
A stated mechanism, relevant conditions, and evidence or a testable prediction justify the proposed directional effect.
Part 2 · Distinguish reinforcing loops and balancing loops
A reinforcing loop amplifies an initial change; a balancing loop opposes it. A link sign describes whether increasing one variable increases or decreases the next, holding the relevant context fixed. In this selected ice loop, more warming reduces reflective ice, and more ice reduces warming: two negative links form a reinforcing loop. Delays and additional balancing processes affect the actual response, so the loop alone does not quantify the final outcome.
Read the visual model
Identify the labeled structures and units, then trace the arrows or compare values under the caption’s stated conditions. Separate the displayed evidence from a further inference. Write your reasoning before opening the guidance.
Does one negative link automatically make a whole loop balancing?
Visual reasoning — after your attempt
No. The product of signs around the closed loop determines this classification; delays and other loops still matter.
A reinforcing feedback amplifies an initial change; a balancing feedback opposes it. Time delays, thresholds, and saturation can alter the eventual behavior. Counting signs can help classify a simple loop, but it does not determine its strength or guarantee a particular time trajectory.
A balancing response arriving late can allow overshoot. A reinforcing loop can weaken when a resource limit is reached.
Pause and explain
Does a balancing loop guarantee immediate stability?
Check your reasoning after answering
No. Delays and other interactions can permit oscillation or overshoot; the loop needs a dynamic and quantitative account.
Part 3 · Separate probability, consequence, and exposure
A simple expected loss multiplies event probability by a consequence on a defined comparable scale, summing across mutually specified outcomes. Probability needs an interval and reference class. Exposure concerns who or what is in contact with the hazard; vulnerability affects the damage given that contact. Two options can have similar expected loss but different worst cases, inequality or uncertainty. Explain these dimensions rather than treating one average as the entire decision.
Read the visual model
Identify the labeled structures and units, then trace the arrows or compare values under the caption’s stated conditions. Separate the displayed evidence from a further inference. Write your reasoning before opening the guidance.
Which scenario has larger expected value, and which has the larger single-event consequence?
Visual reasoning — after your attempt
A has expected 10 versus 7.5 for B, and its consequence 100 is also larger; other scenarios could separate those rankings.
A simple expected-impact model multiplies event probability by a specified consequence for compatible units and interval. Equal expected values can conceal very different distributions or effects on people. Hazard, exposure, and vulnerability describe different parts of a risk account.
A rare high-consequence event and a frequent small event can have equal expected loss but different planning implications.
Pause and explain
Why is expected loss not a complete decision rule?
Check your reasoning after answering
It averages outcomes and can conceal extremes, unequal effects, uncertainty, and constraints that require separate consideration.
Part 4 · Test decisions under uncertain scenarios
A scenario range examines outcomes under explicit uncertain assumptions. It is not automatically a statistical confidence interval or a probability distribution. If a decision ranking changes across plausible inputs, identify the threshold and which new evidence would most reduce uncertainty. Some choices can be robust across a range even when the exact probability is unknown. Keep precaution, cost and fairness priorities explicit rather than converting missing information into a claim that risk is zero.
Read the visual model
Identify the labeled structures and units, then trace the arrows or compare values under the caption’s stated conditions. Separate the displayed evidence from a further inference. Write your reasoning before opening the guidance.
What additional evidence would be most useful if only probability drives a ranking reversal?
Visual reasoning — after your attempt
A better justified event-probability estimate for the relevant place, interval and conditions, with its remaining uncertainty.
Compare plausible conditions and sensitivity rather than presenting one uncertain estimate as certainty. Explain what a model omits and what new evidence could change a decision. Precaution, acceptable risk, and distributional priorities are choices informed by science, not outputs of one equation alone.
A flood intervention can reduce one neighborhood’s exposure while shifting water downstream. Expand the boundary to test that possibility.
Pause and explain
What should be checked when an intervention moves a problem?
Check your reasoning after answering
The wider spatial and temporal impacts, affected groups, and resource transfers need examination beyond the initial site boundary.
Apply the whole unit · Compare simplified annual risk scenarios
Illustrative annual event probability 0.10 and conditional impact 100 units. Proposed action reduces probability to 0.04 but raises conditional impact to 150 units. Treat impacts as comparable model units, not actual insurance or financial estimates.
Your task
Calculate expected impacts and percentage change, explain why lower probability alone is insufficient, and identify distribution and uncertainty questions absent from the simple product.
What your response should show
- Define the system, quantities, units, and relevant conditions before selecting a model.
- Show intermediate calculations or a labeled evidence account, including signs or denominators.
- Explain how the supplied evidence supports the conclusion rather than reporting only an answer.
- Identify a meaningful uncertainty, model limit, or measurement needed to test the conclusion.
Response guidance — after your attempt
Baseline expected impact=0.10×100=10 units/year.
Proposed expected impact=0.04×150=6 units/year.
Expected reduction=(10−6)/10=40%; conditional consequence is nevertheless larger.
The proposal improves this expected-value metric but does not guarantee a smaller impact in every realized year. Event probability, conditional consequence, affected groups, extremes, and parameter uncertainty remain important. The product is a supplied planning model, not a validated assessment of a particular location.
Scientific references and source-model foundations
Parent / teacher teaching notes
Ask students to keep probability and consequence as separate quantities. Require an explanation of what the average conceals and one condition that could reverse the comparison. Ask the learner to explain each symbol, axis, unit and arrow before calculating. Calculated examples, supplied illustrative records and actual historical observations are labeled separately. Selected public OpenSciEd middle-school source figures are foundation examples, not complete high-school editions or an endorsement; all advanced explanations are supplied locally.
The key idea
Conservation, feedback, and explicit risk assumptions make environmental decisions traceable.
Worked examples
Example 1
- Δstorage=50−35=15.
- Final=200+15.
Example 2 · Worked application
- The initial change is declining storage.
- The response reduces withdrawals.
- It opposes the original decline, if effective.
Negative does not mean undesirable.
Example 3
- Multiply probability by conditional loss.
- .02×500000.
Example 4 · Find and fix the mistake
- Test the claim against the stated conditions: Negative does not mean undesirable.
- Reinforcing means amplifying a change, which can be helpful or harmful depending on the goal.
Negative does not mean undesirable.
Example 5 · Reason from the visual model
- A simple expected loss multiplies event probability by a consequence on a defined comparable scale, summing across mutually specified outcomes. Probability needs an interval and reference class. Exposure concerns who or what is in contact with the hazard; vulnerability affects the damage given that contact. Two options can have similar expected loss but different worst cases, inequality or uncertainty. Explain these dimensions rather than treating one average as the entire decision.
- A has expected 10 versus 7.5 for B, and its consequence 100 is also larger; other scenarios could separate those rankings.
Illustrative probabilities and comparable consequence units, not a forecast or insurance estimate.
Avoid these mistakes
- Hazard is not identical to risk; exposure and likelihood matter.
Check your understanding
How can a model be improved after an unexpected result?
Discuss the answer
Check boundary and missing flows, measure uncertain parameters, test alternatives, and update predictions and monitoring.
Return to the phenomenon
Return to the initial case. Why can an average-risk score hide an important tradeoff? Revise your drawing or explanation using two named ideas and one stated limitation.
Compare explanations after your attempt
Expected loss is one summary; scenario ranges, distribution and chosen priorities can change the decision.
What should we investigate next?
Which comparison would test a remaining uncertainty? State what you would change, keep comparable and measure.
Investigate, calculate and revise
Keep a first model and an evidence-supported revision. Attempt each task before opening guidance; all required explanations and supplied-data routes are available locally.
Activity 1 · Return to the opening case
Use the opening phenomenon, unit definitions and explained Parts 1–4.
Your task
Return to the initial case. Why can an average-risk score hide an important tradeoff? Revise your drawing or explanation using two named ideas and one stated limitation.
Success criteria
- Use the stated observations and appropriate units.
- Connect a labeled model with the physical/environmental mechanism.
- State assumptions and an evidence limitation.
- Explain a substantive revision or next test.
Hint
Keep object/material identity, material transfer and energy account distinct.
Response guidance — discuss after your attempt
Expected loss is one summary; scenario ranges, distribution and chosen priorities can change the decision.
Activity 2 · Transfer to a changed case
Cover the worked answer and use the explained models, relationships and notebook.
Your task
Event A has probability 0.05 and consequence 200 units; B has probability 0.20 and consequence 40. Find expected losses and explain why the smaller expected value need not settle the choice.
Success criteria
- Use the stated measurements or conditions, with correct units.
- Connect the result to the physical or environmental mechanism or evidence relationship.
- Identify the assumption, model limit or further evidence requested.
Hint
Name known quantities and conditions, show intermediate steps and check conservation.
Response guidance — discuss after your attempt
A=10 units; B=8 units. B has lower expected loss, but worst-case severity, uncertainty, distribution, constraints and priorities still need transparent consideration.
Words to know
- reservoir
- A stock of material or energy within a defined system.
- feedback
- An effect that returns to influence its own initiating process.
- exposure
- Contact between a hazard and people or ecosystems.
In the real world
Use the chapter investigation to connect this unit to measured evidence and a practical decision.
Exit check
How can a model be improved after an unexpected result?
Check your explanation after answering
Check boundary and missing flows, measure uncertain parameters, test alternatives, and update predictions and monitoring.
Explain your reasoning without notes. If a key idea is missing, revisit the lesson and try again.