Is not the 2nd Law of Thermodynamics always circumvented on Earth? We absorb more energy in the form of light from the sun than we emit.
Also to a very good approximation, we emit what we absorb. When averaged over a long period, that approximation gets better. (It has been somewhat worse over the last century though.)
The atmosphere is a heat reservoir, but just like a water reservoir behind a dam, that doesn't mean it's ever-rising. Energy flows in one side and out the other, but between the two there is room for life.