The Effects of Rising Temperature on Humidity

If you've experienced 90-degree scorchers both in Miami and Albuquerque, you already have some sense of the relationship between temperature and humidity. In fact, what you've experienced is the apparent relationship of the two factors, that is, the way you seem to experience a different temperature according to the humidity. In addition to this perceived relationship, there is the direct effect of temperature on "relative humidity," a separate value related to something called "dew point."

Apparent Change

• Temperature does not directly affect humidity. However, if temperatures rise extremely in a humid place, the air will seem to become even hotter compared with the same temperature reading in a drier environment.

  This perceived difference occurs because of the human body's cooling mechanism. When the ambient temperature increases past a certain point, the body secretes water in the form of perspiration. Sweating helps cool the body only if the water can evaporate; it's the process of evaporation that cools us off. If the ambient air is too saturated with humidity, the sweat doesn't evaporate and we experience seemingly greater heat.

  This phenomenon led to the creation of the "heat index," a measurement based on an algorithm that models humans' apparent sensation of heat based on temperature and humidity.

Relative Humidity

• While rising temperatures do not directly affect humidity, they can affect the relative humidity. Regular humidity simply refers to the amount of water vapor in the air. Relative humidity takes into account the amount of water vapor that can potentially be held in the air before it becomes saturated and forms dew.

  The relative humidity is the ratio of the amount of water vapor in the air compared with the maximum amount of moisture it can hold without producing dew. Therefore, if absolute humidity remains constant and the temperature rises, relative humidity will decrease.

Dew Point

• Increasing temperatures also influence the dew point. Dew point refers to the temperature at which the moisture will turn from vapor to liquid. The maximum potential amount of humidity varies according to air temperature, as evidenced by changing relative humidity. Cooler air holds less moisture than warmer air. This is why dew forms during the night; as the air temperature drops, the air's capacity to hold moisture decreases. While the absolute humidity remains the same, the air becomes less capable of containing the water vapor. Therefore, the relative humidity increases steadily until it reaches the dew point and dew forms.

  If it's incredibly hot and there is only 50 percent humidity, it may still seem extremely stuffy; this is because the hot air can hold a lot of moisture and the dew point is extremely high. Air at a lower temperature would have less capacity to hold humidity and would reach its dew point more easily.