Question: how does the sun make earth hot?

Ciarán O'Brien answered on 14 Nov 2014:

The sun is a giant ball of hydrogen gas that generates heat by nuclear fusion, much like the hydrogen bomb America rather callously dropped on Nagasaki back in World War 2. It generates absolutely amazing amounts of heat this way, and emits it all as electromagnetic radiation (the scientific way of saying light, but mostly at wavelengths we can’t see without special equipment) and solar wind, huge streams of charged, high energy particles that whizz off from the sun much like the steam from boiling water, they just have too much energy to stay part of the thing they came from.

The sun radiates all this radiation and charged particles in every direction, and we’re a relatively small rock 150,000,000 Km away, so the tiniest, tiniest fraction of all that energy makes it to earth. Even so, that tiny tiny fraction of the sun’s energy is still enough to warm up the whole planet.

Some of the radiation makes it through to the ground, and that warms the ground up (and that’s why when the sun pops out from behind a cloud you can feel the heat of it on your skin). Most of the radiation and particle stream get absorbed by the planet’s atmosphere though, and absorbing all this heats up the air to between -50 to maybe 60 degrees Celsius depending on what part of the world you’re in and whether your side of the planet is facing the sun or not.

If the atmosphere wasn’t there, all this heat would bleed back out into space at night time and the dark side of the planet would quickly plunge into really cold temperatures, like maybe 200 degrees below freezing! But the atmosphere acts as a blanket and traps a lot of the heat, so while it’s colder at night (mostly because the radiation that gets to the ground isn’t around to make you feel warm), the blanket of air around the planet makes sure it doesn’t get TOO cold.

(On the other hand, if the atmosphere wasn’t there during the day, ALL the radiation would hit the planet’s surface and probably burn us all alive and boil the oceans away! Nature can be weird like that)

With all the extra carbon dioxide humans have been putting into the atmosphere, the air has been trapping a lot more heat from the sun than it used to, and this has been making the weather misbehave (the air has more heat energy, which makes it move about a lot more) and could make it very difficult to live on the planet in time.