The earth is indeed maintained at a higher temperature than it would otherwise be, all due to the atmosphere. So how does the atmosphere do that? Answer: It has very little to do with CO2, and little (but more) to do with water vapour. During daylight hours, the sun warms the earth. 99.9% (not just 99.0%) of the atmosphere is nearly completely transparent to incoming radiation, but the earth's surfaces absorb a lot of that energy and some parts of it more so than others. This explains why black pavement is so much hotter during hot summer days than is the lighter colored sidewalk right beside the pavement. It is also why we feel cooler in the shade when the temperature of the atmosphere is the same in or out of the shade. Why? Because the vast portion of the atmosphere can't absorb incoming radiation from the sun, but human beings can.
