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Weatherwatch: why cooling white roofs cause neighbours to swelter | Climate crisis
(www.theguardian.com)
this post was submitted on 06 Dec 2024
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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.
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.