--- title: "How do greenhouse gases warm the Earth?" subtitle: "Year 10 Earth and space · Earth's energy balance · Lesson 5" --- # How do greenhouse gases warm the Earth? **Name:** {{field-24}} **Date:** {{field-15}} **Class:** {{field-15}} > **Key question:** The moon is the same distance from the sun as Earth, but its average surface temperature is far below freezing. Earth's thin blanket of gases makes the difference. :::teacher-note **In one sentence:** Students explain how greenhouse gases absorb and re-emit outgoing infrared, distinguish the natural and enhanced greenhouse effect, and locate the mechanism in the energy-balance model (AC9S10U04, node 3, a hinge node). **Students should be able to say:** I can explain that greenhouse gases absorb and re-emit infrared from the surface. I can distinguish the natural and enhanced greenhouse effect. I can explain how more greenhouse gases upset the energy balance and warm the Earth. **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 **How do greenhouse gases warm the Earth?** ☐ They absorb infrared given off by Earth's surface and send some back down, slowing the energy going out ☐ They trap incoming sunlight ☐ They make the sun hotter ☐ They let more sunlight in through a hole in the ozone layer My prediction, and why: {{lines-3}} ::: :::teacher-note **What happens:** They absorb outgoing infrared from the surface and send part of it back down, so energy leaves more slowly. Sunlight passes through them easily. The ozone hole is a different problem. ::: ## Explore Try it on the board in the tutorial. Was your prediction right? What was different? {{lines-2}} ## Explain: natural and enhanced :::keep-together ### Which flow **Greenhouse gases slow which flow of energy?** ☐ Heat from Earth's core ☐ Wind ☐ Infrared going out from Earth to space ☐ Sunlight coming in ::: :::teacher-note **Answer:** Infrared going out from Earth to space ::: :::keep-together ### Natural or enhanced **Natural greenhouse effect or enhanced greenhouse effect?** Groups: Natural, Enhanced - Keeps Earth about 33 °C warmer than it would be with no greenhouse gases: {{field-15}} - Extra CO₂ from burning fossil fuels: {{field-15}} - Water vapour and CO₂ that were in the air before 1800: {{field-15}} - Methane from farming and landfill adding to the air: {{field-15}} ::: :::teacher-note **Answer:** Keeps Earth about 33 °C warmer than it would be with no greenhouse gases → Natural; Extra CO₂ from burning fossil fuels → Enhanced; Water vapour and CO₂ that were in the air before 1800 → Natural; Methane from farming and landfill adding to the air → Enhanced ::: :::keep-together ### Rise and level off **When you raised CO₂, why did the temperature rise and then level off?** ☐ The sun got hotter ☐ CO₂ is hot ☐ The ozone layer got thinner ☐ Less infrared escaped, so energy in exceeded energy out; the warmer surface then gave off more until out equalled in again ::: :::teacher-note **Answer:** Less infrared escaped, so energy in exceeded energy out; the warmer surface then gave off more until out equalled in again ::: :::typical ## Elaborate: the greenhouse gases :::keep-together **Greenhouse gas or not?** Groups: Greenhouse gas, Not a greenhouse gas - Carbon dioxide (CO₂): {{field-15}} - Methane (CH₄): {{field-15}} - Water vapour: {{field-15}} - Nitrous oxide (N₂O): {{field-15}} - Nitrogen (N₂), 78% of the air: {{field-15}} - Oxygen (O₂): {{field-15}} ::: :::teacher-note **Answer:** Carbon dioxide (CO₂) → Greenhouse gas; Methane (CH₄) → Greenhouse gas; Water vapour → Greenhouse gas; Nitrous oxide (N₂O) → Greenhouse gas; Nitrogen (N₂), 78% of the air → Not a greenhouse gas; Oxygen (O₂) → Not a greenhouse gas ::: ::: :::wider ## Elaborate: methane :::keep-together **There is about 200 times less methane than CO₂ in the air, yet it causes about a quarter as much extra warming. Why?** ☐ Kilogram for kilogram, methane absorbs far more infrared than CO₂ (it traps about 80 times as much heat over 20 years) ☐ Methane lasts forever ☐ Methane lets more sunlight in ☐ Methane is hotter ::: :::teacher-note **Answer:** Kilogram for kilogram, methane absorbs far more infrared than CO₂ (it traps about 80 times as much heat over 20 years) ::: ::: ## Evaluate: look back Write one sentence: "At first I thought… Now I think… because…" **Revision summary** - Earth's surface gives off **infrared**. **Greenhouse gases** (water vapour, CO₂, methane, nitrous oxide) absorb some and send part back down: they slow energy **going out**, not sunlight coming in. - **Natural greenhouse effect:** keeps Earth about 15 °C on average instead of about −18 °C. - **Enhanced greenhouse effect:** extra greenhouse gases from human activity reduce the outgoing infrared, so energy in exceeds energy out and Earth **warms** until balance is restored. - It is not the ozone hole. ## Exit ticket :::keep-together **Explain how adding CO₂ warms the Earth.** {{lines-3}} ::: :::teacher-note **Answer:** CO₂ absorbs infrared from the surface and sends some back down, so less energy escapes; energy in exceeds energy out, and Earth warms until it gives off enough to balance again. :::