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Exploring how solar energy reaches Earth and why different surfaces heat up at different rates.
Why does a dark parking lot feel like a hot oven in the summer, while a swimming pool right next to it stays refreshingly cool, even though they've both been in the sun all day?
Everything that happens on Earth—from wind blowing to plants growing—is powered by the Sun. The Sun sends energy through space in the form of solar radiation. This energy travels as electromagnetic waves. When this radiation reaches our atmosphere, about is reflected back into space, while the rest is absorbed by the air, land, and oceans. To keep our planet at a stable temperature, Earth must maintain an energy balance. This means the amount of energy coming in must roughly equal the amount of energy Earth radiates back out into space. If the balance shifts, the planet warms up or cools down.
Quick Check
What must happen for Earth to maintain a stable temperature?
Answer
The amount of incoming solar radiation must equal the amount of energy radiated back into space (energy balance).
Not all surfaces are created equal when it comes to heat. Have you ever noticed that beach sand gets scorching hot by noon, but the ocean water is still chilly? This is called differential heating. Land surfaces (like rocks and soil) are opaque and solid, meaning heat stays concentrated at the very surface. Land heats up quickly but also loses its heat just as fast once the sun goes down. Water, however, is transparent, allowing sunlight to penetrate deeper. It also moves, mixing the heat. Because of this, water takes much longer to warm up and much longer to cool down. This is why coastal cities often have milder weather than cities deep inland.
Imagine a summer day at the coast: 1. The Sun shines equally on the sand and the ocean. 2. By 2:00 PM, the sand temperature reaches because land heats up fast. 3. The ocean water only reaches because it distributes heat deeper and moves constantly. 4. Result: The air over the sand gets hot and rises, while the cool air over the water moves in to take its place, creating a 'sea breeze'.
Quick Check
Which surface heats up and cools down faster: land or water?
Answer
Land heats up and cools down much faster than water.
Why do people wear white clothes in the summer? It's because of albedo. Albedo is a measure of how much light a surface reflects. It is usually expressed as a decimal between and . A surface with an albedo of is a 'perfect absorber' (all energy is soaked up), while an albedo of is a 'perfect reflector' (all energy bounces off). Light-colored surfaces, like snow and ice, have a high albedo ( to ) and stay cool. Dark-colored surfaces, like forests or asphalt roads, have a low albedo ( to ) and absorb most of the Sun's energy, turning it into heat.
This scenario shows how albedo changes can accelerate climate change: 1. Start: Arctic sea ice has a high albedo (approx. ), reflecting most sunlight. 2. Change: As the planet warms, the white ice melts, revealing the dark ocean underneath. 3. Effect: The dark ocean has a low albedo (approx. ) and absorbs much more heat. 4. Result: The warmer water melts even more ice, creating a cycle that speeds up warming.
If a new parking lot is paved with black asphalt, what happens to its albedo compared to the grassy field that was there before?
Why do inland areas (far from the ocean) usually have much hotter summers and colder winters than coastal areas?
A surface with an albedo of 0.9 reflects 90% of the solar radiation that hits it.
Review Tomorrow
In 24 hours, try to explain to a friend why wearing a black t-shirt makes you feel hotter than wearing a white one using the word 'albedo'.
Practice Activity
Go outside and touch three different surfaces (e.g., grass, concrete, a dark car). Rank them from hottest to coolest and try to guess which has the lowest albedo.