Skyhigh

Skyhigh (minor) by Stone Gargoyle

As humans ascend higher into the atmosphere, air density declines. While air composition remains similar, the drop in air pressure, and in return, air volume, effectively makes the respiratory system work much harder in order to supply the same levels of oxygen to the blood stream. In cases where it is impossible to provide similar levels of oxygen to the body, a host of health complications arise, which can potentially result in death. The effective safe limit for breathable air is at 26,000 feet.
To compensate for this, the character can breathe normally at altitudes where the normal limit for breathable air is exceeded by extending the breathable altitude for himself by 1000 feet per level of experience. Her can extend this effect to one other person who is within 100 feet of himself at level one, plus an additional person at levels 4, 8 and 12.