how much fuel

Question
My question is... how much additional fuel is required to boil a given amount of water above 10,000 ft. compared to less than 10,000 ft. My son and grandson are planning a Mt.Ranier climb June 11 and I told them they should plan on taking extra fuel for use above 10,000 ft. as it's going to take longer to boil water in those higher altitudes.They understand that,but want to know how much more. Can you enlighten me on this pressing subject? Thank you, m.k.Arrow

Answer
Dear Mr. Arrow, I climbed Mt. Rainier in 1974, and never went back.  This is outside my expertise as a climber, but I have two degress in physical science, so I am fit to take a shot at it.

Water boils at proportionally lower temperatures as a climber gains height---lower atmospheric pressure allow water to vaporize at lower T.

So, it should take less fuel. That being said, it may take a longer cooking time to achieve the same effect, since boiling is at a lower T.

My guess is, bring extra fuel because you need to drink more hot drinks.

Good Luck