There are several places in the story where one could place the climax. Once he crashes in the wilderness, it is a slow build up as he learns from various incidents how he is going to survive. He learns and learns and gets to the point where he sees the wolves and feels that he has truly changed. He is not afraid the way he used to be, he feels on par with the wolves in a way.
But then, when he has captured another bird, the moose attacks and he is hurt badly during the "madness" of the attack. Once he crawls back to the cave, he hears a strange sound in the wind that eventually becomes a violent storm and a tornado that sweeps through the camp. Once he survives this storm, the tail of the plane is visible, he is able to get into it, get the survival gear and quickly a rescuer appears.
So that storm is certainly worthy of the climax. After learning so much and feeling so confident, it is one last obstacle that could have killed him. But from there is only a short falling action and then the resolution.