Once you get above a certain point in the atmosphere, the temperature skyrockets, since there is no atmosphere to absorb/reflect the heat from the sun. However, even if you were to somehow go outside at this elevation in shorts and a tank-top, you wouldn't feel the heat, since at that elevation, the air molecules are so far apart that the speed at which they are moving is cancelled out by the distance apart that they are.
Hope that helped! =)