Our sun gives us energy. What happens to that energy after we’re done using it? Does it stay here on earth? If it does, won’t it accumulate over time and harm our planet?



Our sun gives us energy. What happens to that energy after we’re done using it? Does it stay here on earth? If it does, won’t it accumulate over time and harm our planet?

In: Earth Science

Earth is warm, which means it emits energy. That energy is mostly in the form of infrared light, which is radiated away into space during the night. At a fundamental level, it’s cold at night because the cold of space works its way down to the Earth when the sun isn’t there to keep it warm. To put it in very ELI5 terms: if your eyes saw different colors, the Earth would glow with its warmth in the same way that a hot piece of metal glows in the colors your eyes can see, and this glow carries away energy.

(Actually, the Earth emits more energy than it gets from the sun – about three parts in ten thousand of this energy come from the Earth’s internal heat, as it continues to cool down from its formation billions of years ago + release energy from all the radioactive materials beneath the surface. This flow was larger in the past, and was once just under 1% of the Earth’s surface energy budget. But the energy from the sun is and always has been the dominant factor.)

Much of it hits our planet and is reflected back off our atmosphere, some is trapped in the atmosphere & becomes heat. Some heats things on earth, like a hot sidewalk in summer. Luckily, earth’s spinning allows much of those things time to cool at night so it’s not a problem. We’re not too close where the heat is too much for things to live & not too far away where the sun doesn’t heat the planet enough. It won’t harm the planet but can harm the things on it. Severe sun damage and sunburn is one of those effects.

It is converted to other kinds of energy.

Plants use it and chemicals to create a kind of energy they can store in the form of sugars and starches.

That energy is later used to do cellular work like build new cells.

Those cells are later eaten by us/animals and used to make their own cells.

The energy never disapears, it just is used for fifferent things. It changes.

The sun warms the earth, the earth radiates heat back out into space. The rate at which those processes happen controls the ambient temperature on earth, which luckily is supportive of life.

Think of it like a pan on the stove. There’s heat energy going in, but it also is losing energy. Depending on how high you turn up your stove those two will balance and it will reach a steady temperature. Like the stove with the pan the sun constantly pumps heat into the planet to stop it cooling down which is a good thing.

Having said that, if you put a lid on the pan it won’t lose as much heat and so the contents will get hotter. This is like what is happening with global warming. Gases that stop the planet giving off as much heat into space are building up and so the planet is warming up.

A large chunk of it just bounces back into space. The earth isn’t black.

Of what is absorbed, the vast majority directly heats the ground, heats the oceans, and heats the atmosphere. This raises the temperature of the earth, and thankfully so or we’d freeze to death.

Now, the sun gives us sunlight because it’s hot (about 5400°C to be specific). The earth is also hot, about say 15°C. Doesn’t seem that hot to us, but it is still 288°C hotter than absolute zero. This means the earth (and everything on it) also glows, just like the sun. We just can’t see it, but a thermal camera can. Tskes about 525°C before we can start to see it as a giant red glow. A light bulb noticably glows at 2400°C. This earth infrared glow all gets sent off into space. It happens day and night, but at night the effect is really noticable without the sunlight heating. Meaning, at night it gets colder, because heat is thrown off into space without any incoming heat.

The warmer the earth gets, the more heat it sends off to space as it glows. 15°C, the current average temperature of the earth, is just the balance. The earth absords sunlight and heats up until it starts to throw off as much heat as it is taking on from the sun. And hotter and the earth would throw more off into space and cool. Any colder and the earth would absorb more from the sun and heat up. It would reach ~15°C eventually.

Now enter global warming. The sun sends us mostly visible light. CO2, methane, and water vapour are transparent to visible light, goes right through. The earth sends off infrared to space. CO2, methane, and water vapour are not transparent to all infrared, the atmosphere isn’t clear to some infrared. This means heat the earth tries to send back out might be blocked by greenhouse gases. This heat the greenhouses gases up, and then they go and emit their own infrared light. But half of that goes into space, the other half goes back down to earth. Greenhouse gases are a one way blanket for the earth. Visible light heat from the sun can come in easily, infrared heat can’t leave as easily. So the earth warms the more CO2 or methane we out in the atmosphere.

A tiny fraction of the heat from the sun does something before becoming general heat that raises the temperature of the earth. Some of the heat drives large scale atmospheric movement, aka wind, due to the temperature imbalances it causes. Same for ocean currents. This motion, wind or currents, eventually just becomes heat though through friction. Plants make sugar with some of the light, and it’s stored as the chemical energy in sugar. As soon as the sugar is burnt, it’s heat. And by brunt I mean a plants own metabolism, the metabolism of an animal (like us) that ate the plant, the plant rots and the bacteria and fungi metabolisms’ use it, or its literally burnt like in a forest fire. As for us, solar panels push some electrons first, before whatever device uses the electricity turns it all into heat. Computer, light bulb, motor, these all eventually make heat.

So it all ends up heat. Unless the chemical energy (sugar) gets buried before it can be burnt. That’s how we have oil, coal, and natural gas. The energy was trapped as chemical energy underground, never burnt. Well, until we dug it up and burnt it. Fossil fuels are using solar light energy from millions of years ago. This would be a miniscule faction of the sunlight coming in though.