Stunning Wet Bulb Temperature Update

The Danger Zone is Far Lower Than We Thought

I searched high and low for a current picture of the killer heat in India. Other than expensive Getty Images, there was nothing. This photo dates back at least six years. It’s almost as if someone doesn’t want us to see the truth.

I published Wet Bulb Temperature Explained just days ago. Since then, I have found new and disturbing information that demands attention. Everyone needs to be aware.

The wet bulb temperature (WBT) of 35° C (95° F) theorized to be the limit to human adaptability to extreme heat in 2009 by Steven Sherwood and Mathew Huber has been proven inaccurate in the first empirical study of human subjects by Pennsylvania State University. The WBT survivability threshold is far lower than assumed from Sherwood and Huber’s work fourteen years ago.

In the study and resulting paper titled, Evaluating the 35° C Wet-Bulb Temperature Adaptability Threshold for Young, Healthy Subjects, eleven males and thirteen females, ages 18-34 were tested for WBT limits in carefully controlled conditions. Daily living activity was simulated by pedaling a cycle ergometer at a low intensity in a range of six carefully controlled temperature and humidity conditions. Skin sensors were placed at the chest, upper arm, inner thigh and calf, and core temperature was measured with gastrointestinal temperature telemetry capsules.

The tests were designed to simulate high humidity and low temperatures conditions, compared to high heat and low humidity conditions.

This study, the first to use direct, scientific physiological observations in examining 35° C (95° F) wet bulb temperature theory as the limit for people in extreme environments, yielded disturbing results. It found that intolerable heat stress in humid environments occurs in young, healthy adults at wet bulb temperatures significantly lower than 35° C, as low as a shocking 25° C (77° F) in hot, dry conditions. In cooler, more humid conditions, that number increased to about 31° C (87.8° F), still four degrees less than the previously assumed 35° C.

This graphic demonstrates the test results. Vapor water pressure (humidity) is measured in mmHg (millimeters of mercury). Three warm, humid environments 36° C (96.8° F) to 40° C (104° F) yielded a WBT of 31° C (87.8° F). Hotter dryer environments 44° C (111.2° F) to 50.6° C (123.8° F) yielded worse results, with WBT ranging from 25° C to 28° C (77° F to 82.4° F). These were young, healthy adults. Our adaptation limits are far below 35° C in all scenarios.

The ramifications of these findings can’t be underestimated. With this four degree swing, people living in the hottest climates such as India, Pakistan, South America, Africa and the Middle East are in far more immediate life and death danger than previously thought. This interactive WBT map demonstrates the point. Roll over the red dots. You will see the newly defined WBT point is already exceeded or at threshold for millions of people from Mexico to northern Australia.

The danger goes well beyond the obvious physical suffering for every person who goes through the agony of dying from their core temperature heating to 104° when organs begin to fail. Lost productivity from every worker who has to toil in the sun affects the world economy, particularly agriculture, where yields are falling precipitously from heat damage and drought as I write. There is less to harvest, and the workers doing this essential labor cannot physically endure these growing, severe conditions. This has obvious consequences for everyone.

The Penn State study doesn’t address other obvious issues (that wasn’t its mandate), such as the impact on natural ecosystems and limits other species have to enduring WBT. I can’t guess about all species, but certainly most mammals have closely aligned thresholds. Here’s what cattle look like when they get too hot.

Kansas 2022, thousands of cattle dead from an historic heatwave. This is what WBT looks like if you can’t escape the conditions.

At 104° F our bodies become hyperthermic. We are in danger of heat stroke and heart failure, among other ugly possibilities. If we reach this state, we will die in six hours or less. Here are some cooling techniques for hyperthermia. Knowing them could save a life. Watch for symptoms such as a rapid pulse, a change in mood or rationality, a lack of sweating, faintness and coma, as identified by the National Institutes of Health.

Also remember, your age and physical condition are determining factors. Your WBT is likely significantly lower if you're older, overweight, or on antipsychotic medication. Children are far more vulnerable, too. Babies don’t sweat, their heads become hot.

In addition to the WBT interactive map, I would like to share this tool with you. It’s a WBT calculator. Remember, WBT is no longer 35° C, it’s 31° C and that only applies to younger, fit people. Your tolerance unless you're in this group is likely far more limited. People die of less heat exposure all the time.

Here is another tool that will help you see what the temperature is projected to be in 2050 if you live in America. You may wish to consider the results in your future plans if you live in already hot conditions. Remember, power grid failure becomes a real possibility with rising temperatures. That air-conditioning, we take for granted, could become widely problematic.

Thank you for reading. Be well.