Balance a four-reservoir carbon model

How does a new transfer change carbon stored in each Earth system?

Submit: An evidence record, explanation and revision.

Related lesson: Climate and Earth Systems

This is a teacher-led extension beyond the short lesson. The task supplies a performance opportunity; completion alone does not certify mastery, full NGSS coverage or state alignment.

Build the idea

A quantitative reservoir model uses stocks and flows with compatible units. Carbon leaving one reservoir enters another unless a transfer across the whole model boundary is explicitly included. Reservoirs can gain or lose carbon even while the total remains constant. Real global fluxes vary; this exercise uses deliberately simplified values.

Evidence and model inputs

Invented annual model, stocks in carbon units: atmosphere 100, biosphere 200, hydrosphere 500, geosphere 1,000. Flows per year: atmosphere→biosphere 20; biosphere→atmosphere 18; atmosphere→hydrosphere 12; hydrosphere→atmosphere 10; biosphere→geosphere 2; geosphere→atmosphere 4. All listed flows occur during the year, with no others. Units are not actual gigatonnes.

Keep actual observations, published findings and invented model cases labeled separately. If a source or required equipment is unavailable, pause that part with a teacher; do not invent results.

Materials and preparation

Paper, graph paper or spreadsheet, and the linked readings.

Grade-level scope

Quantitative model required; clearly distinguish invented carbon units from measured global stocks.

Do the work

1. Draw the four reservoirs and all six directed flows with units.
2. Compute each net change and end-year stock.
3. Check the initial and final total and diagnose any imbalance.
4. Repeat after the geosphere-to-atmosphere flow rises from 4 to 8, keeping other flows fixed for this single-year comparison.
5. Explain why fixed fluxes are a limited assumption over many years and identify feedbacks a more realistic model would need.

Learner worksheet

Write on paper or type here and print. Entries stay in this page’s memory and are lost when you leave or reload; they are not saved or submitted.

Check your reasoning

1. What are baseline net changes A/B/H/G?
2. What is the total before and after?
3. What changes with geological release of 8?
4. Does more atmospheric carbon mean new carbon was created?

Teacher review guide

Review the actual deliverable and discuss the reasoning. For each criterion, use 0 when evidence is absent or fundamentally incorrect, 1 when partly supported with a material error or omission, and 2 when accurate, supported and complete for the stated task. Maximum 8 points is a task score, not a proficiency certification. Give feedback and allow revision.

1. Builds a complete directed stock-flow model.
2. Computes reservoir balances with consistent units.
3. Checks whole-system conservation.
4. Uses a changed flow to explain redistribution and model limits.

Sources and standard reference

• Official NGSS HS-ESS2-6 performance expectation — inspect the practice, core idea, crosscutting concept and assessment boundary.

Instructional text and hypothetical cases are original. Linked source readings supply published evidence where specified. Teachers should judge fit with their course and state requirements.