---
title: "What keeps Earth's temperature steady?"
subtitle: "Year 10 Earth and space · Earth's energy balance · Lesson 4"
---

# What keeps Earth's temperature steady?

**Name:** {{field-24}} **Date:** {{field-15}} **Class:** {{field-15}}

> **Key question:** 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?


:::teacher-note

**In one sentence:** 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).

**Students should be able to say:** I can explain what energy balance means. 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.

**Width:** the unmarked parts are the floor every student does (Engage, Explore, Explain, Evaluate). Typical and Wider sections add contexts, not difficulty. Students work in the online tutorial alongside this sheet.

:::


## Engage


:::keep-together

**Earth absorbs sunlight all the time. Why doesn't it keep getting hotter and hotter?**

☐ The energy is destroyed

☐ The sun switches off at night everywhere

☐ It does keep getting hotter, by the same amount each year

☐ It gives off just as much energy to space, as infrared

My prediction, and why:

{{lines-3}}

:::


:::teacher-note

**What happens:** It gives off energy to space as infrared radiation. When the energy out equals the energy in, the temperature stays steady: energy balance.

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## Explore

Try it on the board in the tutorial. Was your prediction right? What was different?

{{lines-2}}

## Explain: energy in, energy out


:::keep-together

### Balance

**What does energy balance mean?**

☐ Energy absorbed from the sun equals energy given off to space, over time

☐ No energy is moving

☐ Earth stores all the energy it receives

☐ The sun and Earth are the same temperature

:::


:::teacher-note

**Answer:** Energy absorbed from the sun equals energy given off to space, over time

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:::keep-together

### Restored

**After you increased the sunlight, why did the temperature stop rising?**

☐ The sunlight ran out

☐ The ocean got full

☐ A warmer surface gives off more infrared, until energy out matched energy in again

☐ The warmer Earth reflected more of the sunlight

:::


:::teacher-note

**Answer:** A warmer surface gives off more infrared, until energy out matched energy in again

:::


:::keep-together

### How energy moves

**Match each energy flow to how it moves.**

A. Radiation (infrared)

B. Radiation (visible light)

C. Convection

D. Conduction

{{columns 60% 40%}}

{{rows 1}}

| Part | Letter |
|---|---|
| `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` | |

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:::teacher-note

**Answer:** Sunlight reaching the surface → B. Radiation (visible light); Infrared leaving Earth for space → A. Radiation (infrared); Warm air rising from hot ground → C. Convection; Heat passing from warm ground into the air touching it → D. Conduction

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:::typical

## Elaborate: the ocean as a store


:::keep-together

**Why does Earth take decades, not days, to reach a new balance after a change?**

☐ Infrared is slow

☐ Sunlight takes years to arrive

☐ Nothing changes for 50 years

☐ The oceans can store a huge amount of heat, so they warm slowly

:::


:::teacher-note

**Answer:** The oceans can store a huge amount of heat, so they warm slowly

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:::


:::wider

## Elaborate: moving heat around


:::keep-together

**Western Europe is much milder than parts of Canada at the same latitude. What helps explain it?**

☐ Europe has more greenhouse gases

☐ Europe is closer to the sun

☐ Canada has no sunlight in winter

☐ Warm ocean currents carry heat from the tropics across the Atlantic

:::


:::teacher-note

**Answer:** Warm ocean currents carry heat from the tropics across the Atlantic

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:::


## 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.

## Exit ticket

:::keep-together

**What is energy balance, and what happens if more energy comes in than goes out?**

{{lines-3}}

:::


:::teacher-note

**Answer:** Energy in equals energy out over time. If more comes in, Earth warms until it gives off enough extra infrared to balance again.

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