A humid heatwave is expected to affect much of North America in the coming days and our bodies aren’t well designed to deal with it.
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There’s a reason why a 90F day in New York can feel more exhausting than a 100F day in Arizona. It’s not just the number on the thermometer, it’s the amount of moisture in the air.
As Europe continues to feel the brunt of it’s record-breaking heatwave which caused dozens of deaths, North America is bracing itself for a “heat dome” which will bring not only searing ambient temperatures, but humidity levels making the heat unbearable.
Weather forecasts increasingly provide “feels like” temperatures rather than just air temperatures. This is because humidity completely changes the way in which the human body not only perceives, but deals with heat.
Even during exercise or on a very hot day, humans are remarkably good at regulating body temperature at around 98.6F (37°C) by sweating. Sweat itself does not cool the body down, but the process of it evaporating off of the skin and turning into water vapour essentially transports heat away from the body and into the air.
When the air is dry, sweat evaporates quickly and even on very hot days, most people can produce enough sweat to keep their body temperature regulated. In really humid temperatures, the air becomes saturated with water vapour meaning sweat does not evaporate as efficiently, leaving humans in hot, humid environments dripping with sweat as the body struggles to get rid of excess heat.
The consequences are unpleasant, but can also turn dangerous very quickly as body temperature rises. The body attempts to cool by redirecting blood towards the skin and increasing heart rate, placing more strain on the heart. Dehydration can happen quickly as sweating continues in vain. If the body’s temperature keeps on rising, heat exhaustion or heat stroke can develop, the latter being a life-threatening emergency if not quickly addressed.
As fans gather to watch the World Cup across North America, places like Toronto, where Portugal and Ronaldo will be playing on Thursday 2nd July will be facing humid temperatures exceeding 100F. (Photo by Molly Darlington/Getty Images)
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Heat stroke is the most severe form of heat-related illness and is a medical emergency. It occurs when the body’s natural cooling system becomes overwhelmed and can no longer regulate its internal temperature. The CDC says warning signs of heat stroke include confusion, slurred speech, loss of consciousness, seizures, a very high body temperature, and skin that is either hot and dry or heavily sweating.
Without rapid treatment, heat stroke can cause permanent damage to the brain, heart, kidneys and other organs, and may be fatal. Anyone showing these symptoms should be moved to a cool place immediately while emergency medical services are called, as prompt cooling can be lifesaving.