It is my understanding that the reason it gets colder the higher up you go in the troposphere is because you are further from the main source of warmth - the surface level. Many people think that the reason why it is cold is due to the pressure difference but I think this explains more why warm air from the surface cannot distribute it's warmth higher up - because as the pressure drops the temperature drops. Notice that the pressure has to drop for the temperature to change (temp drops because the air parcel loses energy expanding). If the pressure of gas stayed the same, then the temperature would not depend on it's absoute pressure but instead on the amount of energy it gains and loses due to various processes. In fact the adiabatic lapse rate which exlains the loss of energy as a parcel of air moves up tells us that the parcel is often even colder than the surrounding air. Similarly, air descending rapidly down a mountain often gains so much energy that it's temperature can be way higher than the air temperature at the bottom of the mountain was (e.g. Fohn winds). Does anybody disagree with this? Is my understanding lacking something?