Why is cabin pressurization necessary in aircraft?

Cabin pressurization is essential in aircraft for maintaining an adequate air density that is necessary to sustain life, particularly at high altitudes. As an aircraft ascends, the atmospheric pressure decreases significantly, which can lead to hypoxia, a condition that occurs when the body is deprived of adequate oxygen. At cruising altitudes, the oxygen density in the atmosphere is insufficient for humans to breathe comfortably or effectively without additional supplementation. Pressurizing the cabin allows for an environment where passengers and crew can breathe normally, thereby ensuring safety and comfort throughout the flight.

The other options, while they may have relevance in different contexts, do not directly address the primary need for cabin pressurization. Enhancing fuel efficiency and reducing engine noise pertains more to aircraft design and operation, while temperature comfort is a secondary effect of pressurization but not its fundamental purpose.