Earth is in energy balance when the energy it absorbs from the sun equals the energy it gives off to space as infrared. Energy moves between the spheres by radiation, conduction and convection, and the oceans store heat. Upset the balance and Earth warms or cools until it is restored.
In about an hour, the sun pours as much energy onto Earth as humanity uses in a year. Yet, year to year, Earth's average temperature barely changes. Where does it all go?
Sunlight comes in and some is absorbed. This lesson: where that energy goes.
Engage: Commit to a prediction before you test anything. A wrong guess is fine: it shows you what to look for.
Explore: Try it on the board and compare what happens with your prediction.
Explain: Use the particle model to explain what you saw.
Elaborate: Use the same idea in a new context.
Evaluate: Look back at your first ideas and what changed.
WidthMore contexts, same idea.
Make your prediction first. Help opens once you've locked it in.
EngageCommit to a prediction before you test anything. A wrong guess is fine: it shows you what to look for.
Engage: why doesn't Earth keep heating up?
ExploreTry it on the board and compare what happens with your prediction.
Explore: upset the balance
Move the Sunlight or Reflected slider. Then press Run 10 years or Run 50 years and watch the temperature, energy in and energy out.
Try it yourselfYour edits are saved in this browser.
Change the sunlight or the reflection, then run the years until Earth is in balance again.
Use the board. This ticks when you get there.
ExplainUse the particle model to explain what you saw.
Explain: energy in, energy out
In your book: draw a simple energy-flow diagram (sun, atmosphere, surface, ocean, space) with arrows for energy in and out.
Match each energy flow to how it moves.
Sunlight reaching the surface
Infrared leaving Earth for space
Warm air rising from hot ground
Heat passing from warm ground into the air touching it
ElaborateUse the same idea in a new context.
Elaborate: the ocean as a store
Elaborate WiderUse the same idea in a new context.
Elaborate: moving heat around
EvaluateLook back at your first ideas and what changed.
Evaluate: look back
Write one sentence: "At first I thought… Now I think… because…"
Revision summary
Energy balance: energy absorbed from the sun = energy given off to space as infrared, over time. Then temperature is steady.
Upset it (more in or less out) and Earth warms or cools until out = in again.
Energy moves between the spheres by radiation, conduction and convection; the oceans store heat and carry it around the world.
For teachers
Students explain energy balance as incoming absorbed solar energy equalling outgoing infrared over time, describe energy flows between the spheres, and identify the ocean as a heat store (AC9S10U04, node 2, a hinge node). About 22 minutes.
I can explain how a temperature change restores the balance.
I can describe energy flows between spheres and the ocean's role as a store.
Before class
A concept tutorial for introducing or revising the idea. Set the width with ?width=minimum, typical (default) or wider.
The hinge is balance as a dynamic equality (big flows in and out), which the greenhouse lesson then disturbs.
Board notes: a one-layer energy-balance model. Average sunlight 340 W/m², 30% reflected; the surface gives off infrared (σT⁴); the air absorbs part of it and sends half back down. The starting temperature is the model's balance (about 15 °C). A change in sunlight or reflection creates an imbalance; the temperature then moves over a few decades (the model's heat store stands for the upper ocean) until out equals in. Real feedbacks (water vapour, ice, clouds) are left out.
Running the lesson
Engage: count how many chose 'the energy is destroyed'.
Explore: ask what happened to 'energy out' as the temperature rose.
Explain: the 'why did it stop rising' question is the checkpoint.
The hard part (on purpose)
Seeing a steady temperature as energy in equal to energy out, not no energy moving. When a student says nothing moves at balance, ask what the in and out numbers are.
When students get stuck
A student thinks balance means no energy is moving. Ask: What are the in and out numbers? Fix: About 240 W/m² each way: big flows, equal.
Stretch and support
Stretch: If sunlight rose 1%, roughly how much would the model's temperature change? Try it.
Support: Give the diagram with arrows to label: in, reflected, absorbed, infrared out.
Where it leads
Next: the greenhouse effect (node 3). Later: human activity and the energy imbalance (nodes 4 to 6).
What each step is for
Engage: why doesn't Earth keep heating up?: Students who see Earth only receiving energy can't explain a steady temperature; the board shows equal outgoing infrared.
Explore: upset the balance: Changing the energy in and watching the temperature move until out equals in again makes balance a process, not a fixed state.
Explain: energy in, energy out: Defining balance, and locating the flows between the spheres, is the model the greenhouse effect will change.
Elaborate: the ocean as a store: The ocean's heat capacity explains why climate responds slowly.
Elaborate: moving heat around: Ocean currents redistribute heat, explaining regional climates within the global balance.
Now you can
Explain what energy balance means.
Explain how a temperature change restores the balance.
Describe energy flows between spheres and the ocean's role as a store.