After getting into the estimation of calories burned while hiking, someone brought up the fact that I didn't consider the altitude. Well I looked up a review research article and wrote up and interpreted what it said.
Basically they found that cold temperatures were the cause for increased basal metabolic rate at altitude, not hypoxia (although needs many more studies). They also stated that actual work performed at altitude (like hiking / climbing) does not itself need more calories than at sea level. However, the increased intensity due to lower O2 pressure -> burning more glycogen -> eat more carbs.
This was just one review article. Anyone got some other sources?