Researchers at an environmental nonprofit say that the number of days with dangerously humid heat is increasing – particularly in the Midwest and South – and that’s affecting people’s health.
Analysis from scientists at the group Climate Central shows the number of days with heat index values above 90 degrees is increasing in parts of the country, making the air wetter and hotter.
“We know that humid heat is increasing with climate change, because as the temperature gets hotter, it also makes the atmosphere's capacity to hold moisture increase,” said Kaitlyn Trudeau, an applied climate scientist with the group. “So you can think of it like a sponge that soaks up water, but as air gets hotter, it's just basically a bigger sponge.”
Climate Central released a tool in May that shows daily data on where humid heat is increasing around the world.
The trend is most pronounced in the Midwest and southern United States. Amarillo, Texas has 22 more extreme humid days per year compared with 1979, while Tulsa and St. Louis have around five more per year.
The heat index takes humidity into account along with the air temperature. Measures that include humidity, wind and other factors are a better estimate of how dangerous hot weather can be, said John Pike, a meteorologist with the National Weather Service in Norman, Oklahoma.
Sweating is the body’s main defense against overheating, he said. If a person can’t sweat to stay cool, their body temperature rises, which can cause issues with the kidneys, liver and other organs.
When you sweat, that produces what's called evaporative cooling,” Pike said. “If the humidity gets too high, then you won't get that evaporative cooling.”
The weather agency issues heat advisories and warnings when the heat index rises, in the hopes people will take more precautions and be on the lookout for signs of heat stroke.
“It's just really to let people know, just keep an eye on how long you're outside,” Pike explained. “It's also very important to check on the elderly especially if they don't have air conditioning or something in their house.”
Agricultural workers are 'on the front lines'
High humid heat days are especially dangerous for outdoor laborers such as farmworkers.
“Heat is one of those really, really deadly risk factors for farmworkers, and one of the reasons that farmworkers experience such high rates of illness, injury, and death on the job,” said United Farm Workers Vice President Elizabeth Strater.
Unlike other outdoor laborers who may be paid by the hour, farmworkers are usually paid by how much they harvest, she said.
“These workers have ... a financial incentive to push their body beyond what it's able to endure, and they do that out of economic desperation, because farmworkers are also some of the poorest workers in the country,” Strater said. “Farmworkers are really affected, and very much on the front lines.”
Hydration alone isn’t enough to combat heat illness in humid conditions, she added. Workers need to get out of the heat to lower their internal body temperature.
Humid heat also affects how clearly people can think, Strater said, and that can lead to more accidents on the job.
UFW has pushed for stronger worker protections, including paid breaks and adequate shade, to be written into federal law.
Protection against heat “isn’t rocket science,” Strater said. “We know what it takes to keep workers alive in high heat: They need shade, they need paid rest breaks… they need training and information, not only as to what the danger signs are, but what their rights are. And they still do have a right to refuse unsafe work."
The dangers of humid heat show that focusing on high temperatures alone isn’t enough, said Trudeau, the scientist with Climate Central.
“It’s this hidden danger that you can't really tell just from a thermometer,” she said.
This story was produced in partnership with Harvest Public Media, a collaboration of public media newsrooms in the Midwest and Great Plains. It reports on food systems, agriculture and rural issues.
