Iowa faces increased soil erosion, more extreme rain events as humidity becomes a bigger factor in climate change

Climate change was a common topic during Sen. Joni Ernst’s town hall at Coe College. Friday, March 17, 2017. — photo by Zak Neumann.

The old complaint, “it’s not the heat, it’s the humidity,” may soon take on a new ominous meaning, according to the 2017 Iowa Climate Statement. “[T]he rise in ‘absolute humidity’ (moisture in the air) is likely to become the most pervasive factor in climate change across the state,” according to the 190 scientists, researchers and educators from 39 of the state’s colleges and universities who signed the statement.

The statement, which was published on Wednesday, is the seventh annual climate assessment by the state’s leading scientists, but the first to focus on humidity.

“The impact of humidity is often neglected in discussions of climate change,” said Jerry Schnoor, co-director of the University of Iowa Center for Global and Regional Environmental Research. “With climate change, people think of temperature right away, and around here, flooding. But they don’t really think about humidity.”

The statement explains why people should think about it.

For Iowa agriculture, increased warm‐season humidity leads to increased rainfall, extreme rain events, water‐logged soils during planting season, soil erosion and runoff of chemicals to waterways. Rising humidity also leads to longer dew periods and higher moisture conditions that elevate costs of drying grain and increase populations of many pests and pathogens harmful to both growing plants and stored grain. Increased nighttime temperatures coupled with humidity causes stress to crops, livestock and pets and, in extreme cases, heat stress can cause loss of life.

Beyond having an impact on agriculture, “increased moisture in the air accelerates metal corrosion, rot and warping of wood and peeling of paint.” There’s also the personal discomfort humidity causes, as the heat index — what the combination of atmospheric heating and humidity makes feels like to people — increases. More seriously, there are health issues such as asthma and other respiratory problems, that are aggravated by higher humidity.

“I was really surprised and impressed how much absolute humidity has gone up in the state in less 50 years,” Schnoor said.

The statement cites the example of Dubuque, where absolute humidity during springtime increased 23 percent between 1970 and 2017. “Increases in humidity have been measured across the Midwest and in Iowa across all seasons and at all long‐term monitoring stations,” according to the statement.

“The dew points just continue to climb [higher dew points means more moisture in the air], and our temperatures go along with that,” Schnoor said. “Especially our nighttime temperatures. We can’t cool off at night, because there’s so much moisture in the air.”

Unlike previous Iowa Climate Statements, this year’s statement doesn’t include recommendations for specific actions to counter the problem.

“It was a deliberate decision to emphasize awareness of the impacts of humidity, because we thought it was lacking, but also because it’s hard to point to individual actions that can help decrease humidity,” Schnoor explained.

“We need to decrease emissions to address climate change in the longer term. But as humidity continues to increase, we’re going to need to adapt our infrastructure to its impacts.”