Yes, clouds.

With a clear sky, you're radiating (based on your own temperature) out to the blackness of space, which is radiating back at 4 Kelvin. Which is to say, it's contributing basically nothing. You're just giving up heat to the cosmos.

With a cloudy sky, you're radiating (based on your own temperature) out to the bottoms of the clouds, which are reflecting your radiation back to someone else on the ground, and their own heat is reflecting back to you. And such. The cloud looks white in the daytime because it's very reflective, so it acts like a mylar blanket to hold the heat in.

Physics is strange:

> At night, when cloud coverage increases, downwelling infrared radiation also increases. So, clouds act like space heaters, emitting energy towards the ground. Blankets only limit the transfer of heat energy away from your skin(convection).

Huh, that's very interesting and non-intuitive for a non-physicists like me. Thanks for the explanation!

This is what the greenhouse effect is, literally. At "thermal IR" wavelengths the sky is a blanket. Cloudy sky is even more of a blanket.

I live near a grape growing are, and they have wind turbines to blow air on cool nights slightly above freezing because the radiation from the ground to to sky can be enough to frost-damage their crops.

So they turn them on the blow the stagnant warmer ambient air around and mitigate that.

I was told that light reflects heat, and heats more quickly, but also radiates badly (cools more slowly).

This is why heatsinks are often painted black.

It is also the reason for all the strange white/black colors on rockets.

> heats more quickly

Errata: “heats less quickly”.