How hot is too hot for the human body?

For a study published in Nature Climate Change in 2017, Mora and her team analyzed hundreds of extreme heat events around the world to determine which combinations of heat and humidity were most likely to be fatal, and where those conditions were likely to happen in the future.

They found that if today about 30% of the world’s population is exposed to a deadly combination of heat and humidity for at least 20 days each year, that percentage will drop to almost half by 2100, even with the most drastic reductions in greenhouse gas emissions. emissions.

Other researchers have found that climate change causes extreme heat waves up to hundreds of times more likely and causing more than a third heat-related deaths. We are changing our planet, what are the limits of what we can endure?


As warm-blooded mammals, humans have a constant body temperature, around 98 ° F (37 ° C). And our bodies are designed to function pretty well at this temperature, so there is a constant balance between heat loss and heat gain.

The problems start when our body can’t lose heat fast enough (or loses it too quickly in cold weather, but let’s focus on heat for now). When your core temperature gets too high, everything from organs to enzymes can shut down. The extreme heat can lead to major kidney and heart problems, and even brain damage, says Liz hanna, a former public health researcher at Australian National University who studies extreme heat.

Your body works to maintain its core temperature in hot environments primarily by using a powerful tool: sweat. The sweat you produce evaporates into the air, sucking heat from your skin and cooling you.

Moisture paralyzes this method of cooling – if it is so humid that there is already a lot of water vapor in the air, then the sweat cannot evaporate as quickly, and the sweat will not cool you down. not that much.

The extreme heat can lead to serious kidney and heart problems, and even brain damage.

Researchers like Mora and his team often use measurements such as heat index or wet bulb temperature to examine how excess heat and humidity interact. This way, they can focus on a single number to identify unlivable conditions.

The heat index is an estimate that you have probably seen in weather reports; it takes both heat and humidity into account to represent the weather. The temperature of the wet thermometer is literally what a thermometer measures if a damp cloth is wrapped around it. (The temperature in the forecast is technically a dry bulb temperature, as it is measured with a dry thermometer.) The wet bulb temperature can estimate what your skin temperature would be if you were sweating constantly, so it is often used for get closer to the way people would. fare in extreme heat.

A wet bulb temperature of 35 ° C, or around 95 ° F, is roughly the absolute limit of human tolerance, says Zach schlader, physiologist at Indiana University at Bloomington. Beyond that, your body will not be able to lose enough heat from the environment to maintain its core temperature. This doesn’t mean the heat will kill you right away, but if you can’t cool yourself down quickly, brain and organ damage will start.

the conditions which can lead to a wet bulb temperature of 95 ° F vary widely. In the absence of wind and sunny skies, an area with 50% humidity will reach an unliveable wet bulb temperature of around 109 ° F, while in predominantly dry air temperatures would have to exceed 130 ° F to reach this limit.

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