Dangerous Combination of High Heat-Humidity Emerging and Progressing Faster: Report

Human body has evolved to gain a tremendous capacity of adjusting its temperature. The naked skin and the sweat glands constitute a sophisticated cooling system in itself. The sophisticated thermoregulatory system has enabled us to roam over all the continents and adapt accordingly. Nevertheless, this fashionable system of ourselves also has a limit.

The global temperature is continuously on rise, that too, due to anthropogenic activities. The combination of heat and humidity potentially bears bad news for usand has been studied for decades now, especially in military, athletic and occupational contexts. Its impact can be avoided through behavioral adaptations and also through acclimation, but upto a limit. Beyond this limit, the survivability will be at stake even in the most ideal conditions that represent perfect health, total inactivity, full shade and unlimited drinking water. This much is known based on the previous studies, as a representational one can be the study in PNAS. 

The reason for the existence of the threshold of the tolerability of heat-humidity combination is the way the body controls its heat. The internal temperature of the human body lies in the range of 36.8 plus and minus 0.5 degree Celsius. When the skin temperature is around 35 degree Celsius, then the internal heat can be shed out due the gradient in temperature. But when the air temperature rises beyond this limit, the cooling of the body requires the mechanism of latent cooling, which can be done through the sweats. Then, what happens if the air temperature combined with the humidity goes beyond a threshold? 

Here comes the concept of wet bulb temperature (TW) of the human body. The wet bulb temperature for the human body has a threshold of 35 degree Celsius. The simple meaning of this threshold is that the human body would fail to cool itself when the air temperature goes beyond 46 degree Celsius with a humidity level of 50%. This could be a fatal condition as well. Studies have already shown that severe mortality and morbidity occurs at a much lower TW. For example, the heat waves in 2003 in Europe and in 2010 in Russia, had the TW value of 28 degree Celsius. Also, in some studies the estimated time of crossing the TW limit of 35 degree Celsius appears to be emerging several decades from now. 

But, a recent study published in Science Advances says that these projections might be wrong. According to it, such conditions have already emerged in several parts of the globe.  Incidences of extreme heat and humidity, unprecedented, have occurred in parts of Asia, Africa, Australia, South America, North America, and US Gulf Coast regions, according to the study. The researchers spotted more than dozens of recent brief outbreaks of such events. But they lasted only for a few hours; however, worryingly, the frequency and intensity are increasing. 

Cloin Raymond, the lead author of the study was quoted to have said, “Previous studies projected that this would happen several decades from now, but this shows it's happening right now. The times these events last will increase, and the areas they affect will grow in direct correlation with global warming.”

The team conducting the study analyzed data from weather stations in the time period of 1979-2017. Their analysis showed that the extreme heat-humidity conditions have doubled over the period. It said, “Repeated incidents appeared in much of India, Bangladesh and Pakistan; north-western Australia; and along the coasts of the Red Sea and Mexico's Gulf of California. The highest, potentially fatal, readings, were spotted 14 times in the cities of Dhahran/Damman, Saudi Arabia; Doha, Qatar; and Ras Al Khaimah, United Arab Emirates, which have combined populations of over 3 million. Parts of southeast Asia, southern China, subtropical Africa and the Caribbean were also hit.”

The implications of the findings are indeed worrisome. The climate catastrophe, majorly in the form of global warming, is haunting humanity for quite some time. But, at the same time, climate change deniers including Donald Trump, Jair Bolsonaro have continued to undermine action to prevent it. We have already witnessed how the Amazon forests burnt and so did the forests in Australia. One major reason ascertainable is the human-made climate change and global warming. What we need to ponder is how fast we are pushing ourselves towards the threshold of human tolerability.