When we think of climate change, we think of weather events like heat waves, droughts, extreme weather, and rising sea levels. But another important and more insidious impact of climate change is higher humidity levels, especially for the Midwest. Humidity is how much water vapor is in the air. High humidity results in more extreme rain events, mold, mosquitoes, water-logged spring soils, and, of course, uncomfortable summer days.

As temperature levels increase due to global warming, the air can hold more water vapor (4% more for each one-degree increase) leading to the potential for higher humidity levels.

You may have heard the expression: “It’s not the heat, it’s the humidity.” Actually, it’s both. Humidity coupled with temperature to create the “heat index” that is a measure of how hot it feels. For example, a temperature of 92 degrees and dew point of 77 degrees combines to feel like 106 degrees.

The damaging effects of increased humidity rival those of higher temperatures and heavy precipitation and can create unique needs for adapting our infrastructure. Higher humidity accelerates metal corrosion, rot and warping of wood, and peeling of paint. Costs of air conditioning to improve human comfort levels likewise increase with rising humidity.

High humidity can create health concerns. In hot and humid conditions, the efficiency of our bodies to cool by evaporating sweat from our skin slows, making it difficult to maintain a stable core body temperature leading to heat stress and heatstroke.

In addition, the warming of the planet is causing nights to warm faster than days. We can tolerate high temperatures during the day if our bodies can cool during the night. However, higher nighttime temperatures, along with high humidity levels, may not provide the cooling opportunity our bodies need.

High levels of humidity create hazardous conditions for workers and sensitive populations through the danger of heat exhaustion and heatstroke. Allergic rhinitis and asthma are worsened by heightened exposures to mold and dust mite allergens in humid environments. There is also evidence for increased aggression and societal violence associated with hot, humid weather.

This article is part of a series focused on the causes and consequences of a warming planet. See the Ag Decision Maker website (https://www.extension.iastate.edu/agdm/energy.html#climate) for more from this series.