Last updated September 21, 2017

Increased Humidity and Heat Stress

Exposure to extreme heat is already a significant public health problem and the primary cause of weather-related mortality in the US. As temperatures continue to increase due to climate change, heat stress is expected to worsen.

The atmosphere can also hold more water, reducing our bodies’ ability to cool off and increasing our risk of heat-related illness. The Heat Index, also known as the "real feel" temperature, is a measure of how hot it really feels when relative humidity is factored in with the actual air temperature.

US trends

Increasing humidity is contributing to higher nighttime temperatures in the US.[1]


Global trends

The fingerprint of climate change has been found in the increase of wet bulb temperature since 1973, driving heat stress globally.[2]

The northern hemisphere has had increasingly warmer and more humid summers, and the global area covered by extreme water vapor is increasing significantly.[3]