“Wet-Bulb Temperature” – The Limits of Human Endurance and Chaos Ahead

Posted on | October 27, 2015 | 3 Comments

Springfield Republican, Sept. 23, 1988

Mike Magee

On September 23, 1988, I had my first experience with the pressures of a full blown press conference. I was the chief administrative physician at Baystate Medical Center in Springfield, Massachusetts. Our governor, Michael Dukakis, was running for President of the United States, at the same time (as it turns out) that his State Police Academy was running wild.

The cause for the press conference that Friday afternoon was a deadly combination of heat, overexercise, and physical abuse sanctioned and orchestrated by those in charge of the Massachusetts State Police Academy in Agawam, MA, on September 17, 1988. Our assessment a week later of the 51 victims, one of whom would eventually die of massive liver and kidney failure, was that this was the result of a lethal combination of heat, overexercise and dehydration. My public report on camera that afternoon was met with a stern reproach by leaders of our Health System, some politicians, and members of the Dukakis administration. A cover-up by the State Police, who originally suggested the possibility of contaminated water as the cause, was soon revealed. A month later, a full recounting in People magazine confirmed our initial diagnosis, and added as well documentation of extreme physical and verbal abuse that day.

In any case, from that day forward, I’ve been especially conscious of the danger of heat to humans. And so, yesterday, I read with interest on Discovery.com the dramatic headline, “Burning Hell Coming For Mideast Deserts”. The article, based on a recent report in the journal, Nature Climate Change, first exposed me to the term, “wet bulb temperature”. And then today, the New York Times followed up with an article focused on the term called “The Deadly Combination of Heat and Humidity”.

As it turns out, the proper term is “wet-bulb globe temperature” and it was first used in the 1950’s by the U.S. military. The Army and the Marines were attempting to limit the degree of trainee casualty due to heat stress. They had noted that heat measures alone were not an adequate predictor of problems. They sought a measure that would consider humidity as well. So they wrapped a thermometer in a wet cloth, and then took a measure. They then conducted epidemiologic studies and pegged the critical point where injuries began to appear. But, for some reason, wet-bulb temperature measurements and findings never quite made it onto our athletic fields or public health departments.

According to one emergency physician at George Washington Univesity School of Medicine, beyond a certain point, “your body doesn’t cool anymore” (from sweating). So what is that point? Well that depends on what you’re doing. If you are exercising, your body loses the ability to cool itself through sweat evaporation at a wet-bulb temperature of 80. That same person sitting quitely in the shade will first experience problems at a wet-bulb temperature of 92, and if he sadly falls asleep there, under the tree,  at a wet-bulb temperature of 95, he’ll die in six hours. In the Nature Climate Change study, the authors demonstrated that the recent 1.5 degrees of global warming had already resulted in a quadrupling of the likelihood of experiencing exposure to deadly wet-bulb temperatures.

The number of days in danger per year has been averaging four, but if current global warming treads persist, we will experience on average 10 such days per year by 2030. That will seem mild compared to the 17 days in 2050, and even more so compared to the 35 days in 2090. To put some human terms to all this, consider the death rates with heat spells in our recent history: July, 1995 (Chicago) – 700 deaths; August, 2003 (Europe) – 45,000; July, 2010 (Russia) – 54,000. Not small numbers.

India hit a regular temperative of 118 degrees last week with 2500 casualties, which likely triggered the “Burning Hell Coming for Mideast Deserts” article. As one of the Nature Climate Change authors said, “People who have resources will live indoors.” Of course, generating the electricity for air conditioning carries with it a carbon footprint which could make global warming worse. And if you’re poor, you’re out of luck, and on the move to anyplace that’s cooler. Speaking of migration, cultural and historical events like the annual outdoor Muslim pilgrimage to Mecca, Saudi Arabia, could become untenable. The same may be true of oil exploration as equipment breaks down and mechanics can’t function in the extreme heat. If you believe the Middle East is unstable now, don’t expect relief any time soon.

The wet-bulb temperature sets the limits of human tolerance. And clearly human behavior is magnifying our population risks. If we begin to act rationally and adopt policies that lower carbon emissions, we will create for ourselves a range of options and greater freedom. If we persist as we have, expect change similar to what the Massachusetts police cadets experienced in 1988. And as a doctor with first hand exposure to that event, let me tell you, it was not a pretty picture.

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