What happens to temperature as height above the surface of the earth increases?
Temperature decreases with height.
As one moves higher in the atmosphere the temperature drops adiabatically (without addition or removal of heat). This is a bit of a confusing concept, but I will do my best to explain.
The weight of the atmosphere above a particular point is the air pressure or atmospheric pressure. As one moves higher up the amount of atmosphere above to put weight on that point decreases and therefore the pressure is less.
Now, pressure and temperature are directly proportional, that is why a pressure cooker works the way it does. Therefore, as pressure drops the temperature drops, but what is all this "adiabatically" nonsense?
In order to understand why this is an adiabatic process we need to look down to the molecules. Heat is really just the kinetic energy of the molecules of a substance. As the pressure decreases on an air parcel the molecules move further apart. Therefore, even though each molecule may have exactly the same amount of energy that it did before, because they are spaced further apart they interact less often with each other, or with a thermometer if you had one there.
I hope I made that clear. If you need more explanation please do not hesitate to ask.