What traps heat on the planet?
First, there's water. one calorie per degree per gram.
Second, there's the earth crust itself. Just 0.2 calories per degree per gram, but still nothing to sneeze at, and it's heavier than water.
Third, there's the air itself. That's why the ambient temperature at the surface doesn't go near absolute zero at night, but stays only a little lower than daytime temperatures.
Fourth, there's humidity. That's why in tropic regions, the temperature is only a few degrees lower at night than in daytime, while in a desert the temperature can go down by 20 or 30 degrees centigrade.
Fifth? Well, I guess the other greenhouse gasses like carbon dioxide and methane also have some effect. Not nearly as much as the sun and the previous four.