Answer:
Air Pressure: As the mountain climber climbs a mountain, the atmospheric pressure will decrease as there will be less air above him. This will result in lesser oxygen for the mountain climber to breathe.
When the mountain climber descends back to his camp, the air pressure will start increasing and hence he will also attain more oxygen for breathing.
Temperature: A decrease in air pressure means that the molecules of the air will expand. This will result in decrease in temperature. As the mountain climber will ascent on the mountain, the temperature will decrease.
When the mountain climber will descend back to the the camp, the temperature will start increasing.