Earth and Environmental Science · 35 minutes
Suggested grades 9–12 · Unit 2: Carbon and Resource Decisions · Lesson 1 of 2
Keep Stocks Separate From Carbon Flows
Account for annual carbon transfers across interacting reservoirs.
Mr. S Teaches · Original starter lesson · HS-EARTH-03 · Grade range is planning guidance.Watch, notice, discuss
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The Hydrologic and Carbon Cycles: Always Recycle! - Crash Course Ecology #8
By CrashCourse
Identify reservoirs and transfers, then separate an amount stored from a transfer per unit time.
Open on YouTube: The Hydrologic and Carbon Cycles: Always Recycle! - Crash Course Ecology #8 (opens a new tab) ↗Climate change: Earth's giant game of Tetris - Joss Fong
By TED-Ed
Compare the accumulation analogy with the lesson’s stock-flow arithmetic; the animation is background, not a numerical projection.
Open on YouTube: Climate change: Earth's giant game of Tetris - Joss Fong (opens a new tab) ↗What idea from the video helps you calculate net reservoir changes and explain how a transfer can conserve carbon while increasing atmospheric stock? Identify one useful example and one limit of the video's model or explanation.
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Learning objective
Calculate net reservoir changes and explain how a transfer can conserve carbon while increasing atmospheric stock.
Before you begin
- Distinguish a total amount from an amount per year.
Gather your materials
- Paper or notebook
- Pencil; calculator optional for numerical work; all task data supplied below
Language to know
- reservoir
- A place where a substance is stored in the model.
- flux
- An amount transferred per unit time.
- stock
- The amount present at a stated time.
Understand the concept
Fictional annual carbon model: Atmosphere stock begins at 1,000 units. Atmosphere→land transfer is 20 units/year; land→atmosphere 18; atmosphere→ocean 12; ocean→atmosphere 10. An additional 8 units/year moves from a fossil reservoir to atmosphere. These are classroom values, not current Earth measurements. Stocks and fluxes have different units. Carbon entering one included reservoir leaves another; atmosphere can gain carbon even when total modeled carbon is conserved.
Teach it step by step
- Translate the text into reservoir boxes with stock labels and annual flux arrows.
- Calculate atmosphere’s total inflow and total outflow separately.
- Determine its end-of-year stock under the constant-flow assumption.
- Trace the opposite changes in land, ocean and fossil reservoirs to check the total carbon account.
Make the thinking visible
Worked example or model response
Atmospheric inflow is 18+10+8=36; outflow is 20+12=32, so it gains 4 and ends at 1,004. Land gains 2, ocean gains 2 and the fossil reservoir loses 8. The combined change is 4+2+2−8=0.
Guided practice
Together calculate the atmospheric change if the fossil transfer were 3 instead of 8, with all other modeled flows unchanged.
Independent practice
Draw the complete model and calculate end-of-year atmospheric stock in both cases. Explain why assuming the same flows for fifty years would be a strong additional assumption, not a result established by one year.
Quick assessment
Can you add a stock of 1,000 units directly to a flux of 20 units/year without specifying a time interval?
Answer key & assessment criteria
Answers and teaching guidance
- Guided: Inflow becomes 31 and outflow remains 32; atmosphere loses 1 unit and ends at 999.
- Independent: Stocks are 1,004 and 999. All reservoir changes must balance, and long extrapolation assumes unchanged flows despite possible feedbacks.
- Quick check: No. The quantities have different dimensions; a flow must be converted to an amount over a stated interval by multiplication when the flow is constant.
Look for: Assess the stated objective using the concrete criteria and explanations in the answer key. Invite an alternative supported solution; distinguish a model’s prediction from an established observation.
Make it work for your learner
More support
Use separate stock and annual-flow colors and a completed inflow/outflow organizer.
Extension challenge
Introduce a rule that one flux changes with stock and perform two annual arithmetic updates to show how a fixed-flow extrapolation can fail.
Verified references · Selected contributions
Standards connections
Selected NGSS high school-band contribution; full performance requires additional evidence and instruction.
Subject-content standards
These records identify the part of a subject standard practiced here. Course placement is instructional guidance; the source’s category or band remains authoritative.
Contributes to NGSS performance expectation
HS-ESS2-6
NGSS · High school band
Model carbon exchanges among Earth systems quantitatively.
Read the official performance expectation ↗This selected four-reservoir quantitative model omits many carbon pathways and real-world feedbacks. It uses invented values and does not represent a validated Earth-system simulation.
Verified 2026-11-04. Selected contribution, not full attainment.
Supporting literacy connections
These records apply to the specified reading, writing or communication task. They do not establish subject-content alignment.
Supporting Common Core literacy connection
RST.9-10.7
Common Core · Grades 9–10
Translate technical prose into visuals and explain mathematical or visual information.
Read the official standard ↗The activity explicitly analyzes the provided technical text, table or model. It contributes selected literacy practice rather than complete grade-band reading coverage or independent subject-content alignment.
Verified 2026-11-04. Selected contribution, not full attainment.