The important thing is that the high albedo material has to convert incoming light into a particular wavelength of infrared light that is not absorbed by the atmosphere and so it flies straight out into space. If it’s just white (high albedo) but doesn’t convert light into the right wavelengths of infrared light, then yes, it will warm the surrounding areas because a lot of the light it’s reflecting will get reflected off the atmosphere back down somewhere else.
Wikipedia has a thorough article on it: https://en.wikipedia.org/wiki/Radiative_cooling
Here’s a video by a channel called NighthawkInLight: https://youtu.be/KDRnEm-B3AI?t=78
And here is a 2 part series by TechIngredients: https://www.youtube.com/watch?v=5zW9_ztTiw8 https://www.youtube.com/watch?v=dNs_kNilSjk
Things appear white because they are reflecting a lot of light in the visible wavelengths you can see, to which the atmosphere is unsurprisingly transparent. Things that are black on the other hand absorb the light, heat up and re-emit at their thermal temperature which in the terrestrial range of 0-100 degrees peaks in the far infrared which the atmosphere is not (as) transparent to.
The linked study is talking about a boundary effect between the cooler area of high albedo (because painting things white does reduce the energy absorbed and reflects a good chunk of that back into space) and the warmer area of normal albedo. Its modelling how that change between different temperature areas affects air circulation and cloud cover, not that the reflected light is warming up other areas.
to which the atmosphere is unsurprisingly transparent.
The sky is blue specifically because that’s wrong.
so it’s blue because specifically that wavelength of light is scattered, not the rest of it. it’s not reflection, it’s refraction.
You are within sight of a blue LED. Does that monochromatic blue look like the blue of the sky? No. Because Rayleigh scattering diffuses higher wavelengths more, not exclusively.
Even a deep red sunset scatters enough light to overwhelm the stars.
Cooling paint emits light deep enough in the infrared that this effect becomes negligible. It proportional to frequency, to the fourth power.
The sky is not emitting light, it is refracting light, like a prism. A blue LED is emitting light at different wavelengths than the blue of the sky.
… no shit.
Like a prism, it affects all wavelengths. If it was “specifically that wavelength,” “not the rest of it,” it would be monochromatic. Like an LED. But it’s not. Rayleigh scattering diffuses any near-visible photons, at a rate proportional to their frequency, squared, squared.
That’s why cooling paint works differently than merely reflecting light. Even red light can scatter in the air and warm up the environment. Red scatters less than blue… but infrared scatters less than anything visible.
Alright, I’m trying to say that “mostly transparent” is a fine way to describe it.
I was thinking of lining my roof with tinfoil. Would that be a better option or would that just make it worse?
NighthawkInLight has lots of great stuff, but his subambient temperature paint videos are the best.
Chuckle. Taking bets for what the humans will actually learn from this based on their actions.
😭
