Sunday night science question

As many of you know, I roast my own coffee beans in a small roaster. We recently moved from southern California to Utah, going from about sea level in elevation to 6,000 feet.

In Utah the beans roast much faster than at sea level. This is with same beans, weight of beans, roasting time, and roaster.

So, why do they roast faster?

(My father-in-law knew, but then, he’s an engineer)