What is the atmosphere like in most caves?

Unlike the surface environment that is very changeable, cave environments are constant. It is a world of total darkness, constant temperature and high humidity. The animals that live in caves must not only adapt to these conditions, they must live in an environment where there is very little to eat.

The quality of cave air is usually good. The air’s often cool temperature gives it a fresh feeling many people enjoy. Doctors in several countries recommend Speleotherapy for several ailments, occasionally prescribing sitting in a cave to breathe the air.

Karst caves formed in carbonate rocks (limestone, dolomite, and marble) occasionally have slightly elevated levels of carbon dioxide in the air. As water and air move down through fractures in the rock into a cave, they carry carbon dioxide generated in the soil and released by plants through their roots. The typical levels of carbon dioxide are low and not noticed by visitors.

On occasion and usually in certain geologic areas, the levels of carbon dioxide are high enough to cause discomfort. In rare circumstances, carbon dioxide can reach dangerous concentrations. Because air with high concentrations of carbon dioxide is heavier than normal air, it concentrates in deeper sections of caves, and the presence of higher than normal carbon dioxide is usually noticed readily in shallower areas.

The significant presence of other gases in caves is uncommon to rare. Examples include methane from the decomposition of large volumes of organic material which washed into a cave, ammonia from large deposits of bat guano, and a variety of possible gases associated with geothermal areas.

The temperature in caves tends to stay the same year-round, because they’re underground and not affected by surface weather patterns.

The temperature of a cave is usually close to the average annual temperature for the region where it’s located. For example, caves in Texas can be as warm as 70º F. Caves in Missouri might be between 55º F and 60º F. Caves in Wisconsin might be a chilly 50º F.

In the summer, there is almost no airflow. In the winter, cold air penetrates along the entrance shaft and must exit to the surface.

Air pressure inside a cave always tries to equalize with the outside air pressure. If air pressure outside the cave is greater, air moves into the cave and vice versa. Also, winter air is colder and thus denser than cave air, moving down cave floors and pushing warmer air out of a cave along with the ceiling.

References

The Biology of Caves

Cave Climates 

How cool are caves?

How do caves breathe?