Ah sorry, after making controversial statements I had so many comments I ended up getting them mixed up in my head.

Radiant sky cooling is some cool shit, it almost seems like magic. But first I'll be clear that I don't think of this as an alternative to the real solution to climate change, i.e. stop using fossil fuels. I'm not proposing we cover the Earth with it or use in attempts to manage global temperature. While it does have tiny global effects, like a normal solar panel, I'm speaking of their local use, where it can save lives and make the climate change we've already caused tolerable to those who use it.

So, you may have heard in recent years about super black paints or super white paints? I'm I'm sure you're aware of the "heat island effect" and how black roads get very hot vs the white sidewalk.

So those color based effects caused by absorbing/reflecting more or less visible light. Now, no matter how white the paint is, even 100% reflectivity, at best it could absorb less heat. If you measure it it's going to be the temperature of the environment.

Now you are likely also aware that everything, you, your shoes, a rock, a book, everything emits infrared energy, and we can see this with an infrared camera, I'm sure you've seen images on tv or whatever. Now, if everything is emitting energy, why doesn't everything get cold? Well because everything in the environment is radiating energy back at everything else causing equilibrium.

So here's the super cool part...

There's a small window in the electromagnetic spectrum within the infrared range that is able to pass through the Earth's atmosphere without being absorbed. This happens all the time, it's why clear nights are colder, because the Earth is able to more effectively radiate energy out into space.

Well certain materials emit most of their infrared energy within this spectrum. First we found some barium based compounds but they were hard to produce and are not really for sale yet.

But calcium carbonate -- chalk -- also works, almost as good. Using chalk (and you can make it into paint but it has to be done in special way to control particle size to prevent light from passing through and heating up the surface) you can radiate more infrared into space than is absorbed by the environment, cooling the surface to well below ambient temperatures. If you paint the roof of a house with this stuff (and testing and math has been worked out by scientists here) it can have an effect on the level of runnning an air conditioner! Using 0 energy and some chalk! And it works at night even better because it doesn't work by reflecting sunlight, it's radiating infrared directly into space, losing energy to space and cooling down.

Ancient peoples were able to actually make ice using this technology.

https://www.youtube.com/watch?v=KDRnEm-B3AI