Thermodynamics is a series of physical laws...and the second one states that neither heat nor energy EVER move spontaneously from cool to warm.
That's right thermodynamics is a series of laws. Yes, neither heat nor thermal energy can move spontaneously from cool to warm objects.
Neither heat, nor any sort of energy...the second law is universal...it applies to all sorts of energy whether it be stored potential energy created by holding a rock up above the ground or IR radiation emitted from a CO2 molecule...
poor SSDD has some serious misconceptions about physics. basic laws are fundamental but they are still only single factors that need to be taken in combination with all the factors involved.
The Sun is a huge source of highly ordered energy that does work on Earth systems. Our atmosphere is only present because of stored solar energy that is constantly being refreshed to replace energy lost to space.
The radiation produced by the atmosphere (some of which returns to the surface) comes directly and indirectly from the Sun. It is not just an object at a defined temperature. Likewise the surface is also producing radiation from energy received directly and indirectly provided by the Sun.
Both the surface and the atmosphere produce radiation according to their temperature and emissivity. All the time, in all directions. If the surface is warmer than the atmosphere then heat (net energy) moves towards the air. If the atmosphere is warmer than the surface then heat moves towards the surface, but the radiation is always there. No exceptions, no throttling down, no restricted directions.
There is nothing special about the temperature of any object or environment. Sometimes they are a heat source, sometimes they absorb heat. But they always radiate according to their temperature and emissivity. Heat moves to the cooler object whether the differential is 50C-40C, or 20C-10C.
The part that seems to confuse most people is when the radiation from each object is considered individually. An object at 16C radiates about 400W, 15C at 395W, 17C at 405W. The 16C object would be losing 5W to the 15W object, gaining 5W from the 17C object. As long as any of the objects remain at their original temperature their radiation output remains the same.
I do not necessarily agree with Trenberth's numbers but it is illustrative. The Sun adds ~160W to the surface directly
(and an unknown amount of energy has already been stored in the atmosphere). But the surface radiates at ~ 400W. The deficit must be made up from somewhere. It comes from radiation returning from the atmosphere. Trenberth says that ~60W is radiated away, ~100W is carried upwards by the water cycle, which balances out the ~160W received from the Sun. We can argue the numbers endlessly but the general explanation is correct. The surface cannot fully shed energy by radiation because the temperature differential between the surface and atmosphere is much smaller than surface directly to space. The atmosphere is warm because it absorbs a considerable fraction of the surface radiation (indirect sunlight energy).