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Index)
An object can warm through the absorption of electromagnetic radiation (EMR). However, an object passively warmed can't warm the object providing the warmth. Were this to be so energy could be multiplied for no extra input merely by having objects mutually radiate EMR. But there is no such temperature multiplication because the amount mutually exchanged cancels. It does not add as is required by greenhouse theory.
The reason that an object can be heated by EMR on earth by the sun is because the sun is warmer than the earth. The idea of the greenhouse effect is that the cooler, upper layers of air are able to warm a warmer ground by backradiation. But this can not happen.
Greenhouse theory would even require that the backradiation from the earth to the sun warms the sun by a small (if practically imperceptible) amount. This is impossible too because a cooler object can not warm a warmer one unless work is done. But greenhouse gas, not having an energy source, can not provide this work nor can the earth provide work to the sun.