The sun is Earth's main energy source. Some sunlight is reflected straight back to space and the rest is absorbed and warms the planet. How much is reflected (the albedo) depends on the surface: ice reflects most, oceans and forests absorb most.
Fresh snow reflects about 80% of the sunlight that hits it. The open ocean reflects about 6%. When sea ice melts, that difference matters for the whole planet.
To understand climate, start with the energy coming in.
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: does all sunlight warm the Earth?
ExploreTry it on the board and compare what happens with your prediction.
Explore: change the surfaces
Click a surface to change it, or use the buttons. Watch the white reflected arrows and the absorbed energy.
Try it yourselfYour edits are saved in this browser.
Change the surfaces until you have seen the percentage reflected change by at least 30 points.
Use the board. This ticks when you get there.
ExplainUse the particle model to explain what you saw.
Explain: absorbed and reflected
In your book: draw sunlight hitting ice and ocean side by side, with reflected and absorbed arrows of the right sizes.
Reflects most sunlight, or absorbs most?
Fresh snow
Open ocean
Sea ice
Dark forest
Thick white cloud
Elaborate TypicalUse the same idea in a new context.
Elaborate: the angle of the sun
Elaborate WiderUse the same idea in a new context.
Elaborate: land use
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
The sun is Earth's main energy source: about 340 W/m² on average at the top of the atmosphere.
Some sunlight is reflected (about 30% on average: the albedo); the rest is absorbed and warms Earth.
Bright surfaces (ice, snow, cloud) reflect most; dark ones (ocean, forest) absorb most. Melting ice means more absorbed.
For teachers
Students identify the sun as Earth's energy source and explain why different surfaces absorb or reflect different proportions of sunlight (albedo) (AC9S10U04, node 1, a hinge node). About 18 minutes.
I can identify the sun as Earth's main energy source.
I can distinguish absorbed from reflected sunlight with examples.
I can explain why melting ice increases the energy absorbed.
Before class
A concept tutorial for introducing or revising the idea. Set the width with ?width=minimum, typical (default) or wider.
The hinge is the absorbed–reflected split: without it students can't explain why surface changes alter the energy balance (node 2), or why the greenhouse effect is about outgoing, not incoming, energy (node 3).
Board notes: surface albedos are typical values (ocean 6%, forest 15%, city 12%, grassland 25%, desert 35%, ice and snow 80%). The absorbed figure uses Earth's average incoming sunlight (340 W/m²) for the surfaces shown; the whole planet's 30% includes clouds, which the row doesn't.
Running the lesson
Engage: count how many chose 'all of it warms the Earth'.
Explore: ask which button changed the reflected percentage most.
Explain: the melting ice question is the checkpoint.
The hard part (on purpose)
Linking a surface's albedo to how much energy it absorbs. When a student guesses from shininess, ask what percentage the board gives for that surface.
When students get stuck
A student says the ocean reflects a lot because it's shiny. Ask: What percentage does the board give? Fix: About 6% on average: water reflects only at low sun angles.
Stretch and support
Stretch: Melting ice absorbs more, which warms, which melts more ice. What kind of feedback is that?
Support: Give a table of surfaces to rank by percentage reflected.
Where it leads
Next: energy balance between the spheres (node 2), then the greenhouse effect (node 3).
What each step is for
Engage: does all sunlight warm the Earth?: Students who treat sunlight as uniformly heating Earth miss reflection; the board splits incoming light into reflected and absorbed for each surface.
Explore: change the surfaces: Changing surfaces and watching the reflected and absorbed amounts shift makes albedo a measurable property.
Explain: absorbed and reflected: Ranking surfaces and predicting the effect of change is the base the energy balance builds on.
Elaborate: the angle of the sun: Angle of incidence explains why the poles get less energy, linking to Year 7 seasons.
Elaborate: land use: Predicting the local energy effect of land-use change applies albedo to human decisions.
Now you can
Identify the sun as Earth's main energy source.
Distinguish absorbed from reflected sunlight with examples.
Explain why melting ice increases the energy absorbed.