These late August days in Minnesota bring back poignant memories of the treasured time after the dog days of summer with the start of school looming. The cool breezes of late summer provided welcome relief for the sleepless nights spent sweltering on the top level of my bunk on the second floor of our two-story house in our un-air-conditioned bedroom.
Now comes the bad news from the National Oceanic and Atmospheric Administration (NOAA) that the average overnight temperature in the USA this July was the hottest on record.* But the good news is that the great majority of households nowadays (as of 2020) feature A/C. For the cool stats, see this 8/15/22 post by the Energy Institute on How Many U.S. Households Don’t Have Air Conditioning.
I never paid much attention to heat and humidity until my undergraduate studies in chemical engineering at the University of Minnesota. Then I came to appreciate the impact of ambient conditions. Our lab instructor taught us how to measure moisture in the air via a sling psychrometer such as the one demonstrated very delightfully “down under” here. The resulting reading is called the wet bulb temperature.
If you must venture out into the mid-day sun, be careful not to go beyond what your body can balance for the heat. As reported here on July 6, researchers at Penn State University (PSU) discovered that “heat + humidity gets dangerous faster than many people realize.” Their findings came from experiments on 25 young adults who each swallowed a small telemetry pill, which monitored their core temperature. Previous studies** suggested that most people can tolerate a wet-bulb temperature of up to 95 degrees F. But the new data from PSU lowers this limit to 88 degrees.
“When the body overheats, the heart has to work harder to pump blood flow to the skin to dissipate the heat, and when you’re also sweating, that decreases body fluids. In the direst case, prolonged exposure can result in heat stroke, a life-threatening problem that requires immediate and rapid cooling and medical treatment.”
– W. Larry Kenney, Professor of Physiology, Kinesiology and Human Performance, Penn State, and his PSU H.E.A.T Project team
The tolerance to heat and humidity is certainly even less for people over 65, who, according to the PSU researchers comprise 80-90 percent of heat-wave casualties. They will now shift their experimental focus to this older generation.
Be careful out there!
* “The U.S. in July set a new record for overnight warmth”, The Associated Press, August 13, 2022.
** Sherwood & Huber, “An adaptability limit to climate change due to heat stress”, Proceedings of the National Academy of Sciences (PNAS), 5/3/10, 107 (21) 9552-9555.