--- marp: true theme: default html: true --- # Where does the sunlight go? Year 10 Earth and space · Earth's energy balance --- ## Today **We are learning to** 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. - 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. --- ## Why it matters > 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. --- 💬 Discussion ## Engage: predict **Sunlight reaches the Earth. What happens to it?** - Some is reflected straight back to space and the rest is absorbed: how much depends on the surface - All of it warms the Earth - It is stored in the sun's rays - It all bounces off --- ✍️ Activity ## Explore it {{embed: https://studio.learningwaypoints.com/tutorials/_playground-board/index.html?id=deck%2Fscience%2Fearth-10%2Fsunlight%2Fstep-2&code=widget%3A+climate%0Amode%3A+albedo%0A&fresh=1}} [Open this step in the tutorial](https://studio.learningwaypoints.com/tutorials/science/earth-10/sunlight/?full=step-2#step-2) --- ✅ Check ## What happened? * Some is reflected and the rest is absorbed. On average Earth reflects about 30%, mostly from clouds, ice and bright surfaces. Dark surfaces like oceans absorb most of what hits them. --- ✅ Check ## Reflect or absorb **Reflects most sunlight, or absorbs most?** Groups: Reflects most · Absorbs most Fresh snow · Open ocean · Sea ice · Dark forest · Thick white cloud * Answer: Fresh snow → Reflects most; Open ocean → Absorbs most; Sea ice → Reflects most; Dark forest → Absorbs most; Thick white cloud → Reflects most --- ✅ Check ## Melting ice **Arctic sea ice melts and is replaced by open ocean. What happens to the energy absorbed there?** - It stays the same - It decreases - It increases, which warms the area and melts more ice - The ocean reflects more * Answer: It increases, which warms the area and melts more ice --- ✅ Check ## Light or dark **Why does fresh snow reflect most of the sunlight that hits it, while the open ocean absorbs most?** - Water is wet, so it soaks up the light - Snow is cold, so it can't take in any energy - Light-coloured surfaces reflect most of the light that hits them; dark surfaces absorb most of it and warm up - The ocean gets more sunlight, so it absorbs more * Answer: Light-coloured surfaces reflect most of the light that hits them; dark surfaces absorb most of it and warm up --- ✅ Check ## Elaborate: the angle of the sun **The same sunlight hits the equator nearly straight on, but the poles at a low angle. Why do the poles get less energy per square metre?** - There is no sunlight at the poles - The poles are farther from the sun - The same beam is spread over a bigger area, and more is reflected at low angles - The sun is dimmer there * Answer: The same beam is spread over a bigger area, and more is reflected at low angles --- ✅ Check ## Elaborate: land use **A city replaces grassland with dark roads and roofs. What happens to the local energy budget?** - Less is absorbed - The city reflects more - No change - More sunlight is absorbed, so the city warms: an urban heat island * Answer: More sunlight is absorbed, so the city warms: an urban heat island --- ## 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. --- ✅ Check ## Exit ticket **Why does replacing sea ice with open ocean warm the area?** * Ice reflects most sunlight (about 80%); dark ocean absorbs most (reflects about 6%), so more energy is absorbed.