Final answer:
The wet-bulb temperature can never be higher than the dry-bulb temperature. High humidity can inhibit evaporation, making us feel hotter, but it does not increase the wet-bulb temperature, which is linked to the lowest temperature water can reach through evaporation at a given set of conditions.
Step-by-step explanation:
Under no conditions can the wet-bulb temperature be higher than the dry-bulb temperature. Wet-bulb temperature is a measure of the lowest temperature that can be reached under current ambient conditions by the evaporation of water only.
The wet-bulb temperature is always equal to or lower than the dry-bulb temperature, which is the actual air temperature. When we discuss relative humidity, it’s important to understand that it indicates how much water vapor is in the air compared to the maximum possible amount at a given temperature.
High humidity leads to reduced evaporation rates due to the decreased difference in water vapor pressure between leaf and atmosphere. The expression "it's not the heat, it's the humidity" suggests that high humidity can make us feel hotter because it inhibits the evaporation of sweat from our skin, which is our natural cooling mechanism.
On the other hand, low humidity might lead to discomfort due to excessive drying, but it does not increase the wet-bulb temperature. As the air's ability to hold water vapor increases with temperature, the evaporation becomes more effective in warmer air conditions, further highlighting why the wet-bulb temperature never exceeds the dry-bulb temperature.