How hot is too hot for the human body?

For one Learn Published in the journal Nature Climate Change in 2017, Mora and his team analyzed hundreds of extreme high temperature events around the world to determine which combinations of high temperature and humidity are most likely to be fatal, and these conditions may occur in the future The place.

They found that although about 30% of the world’s population is exposed to deadly heat and humidity for at least 20 days a year, by 2100, even if greenhouse gas emissions are significantly reduced, this proportion will increase to nearly half . emission.

Other researchers have found that climate change is creating hundreds of extreme heat waves More likely And lead to More than one-third The number of deaths related to high temperature. We are changing our planet-what is the limit we can endure?

cool down

As warm-blooded mammals, humans have a constant body temperature of around 98 °F (37 °C). Our body is designed to work at that temperature, so there is a constant balance between heat loss and heat gain.

The problem begins when our body cannot dissipate heat fast enough (or dissipate heat too fast in the cold, but let us focus on the heat for now). When your core temperature becomes too hot, everything from organs to enzymes shuts down.Extreme heat can cause serious kidney and heart problems, and even brain damage, says Liz Hannah, A former public health researcher at Australian National University, researching extremely hot.

In a hot environment, your body uses a powerful tool to maintain its core temperature: sweat. The sweat you produce will evaporate into the air, absorbing heat from your skin and cooling you down.

Humidity will weaken this cooling method-if the air already contains a lot of water vapor, then the sweat will not evaporate so fast, and sweating will not cool you down.

Researchers like Mora and his team often use indicators such as heat index or wet bulb temperature to consider how overheating and humidity interact. In this way, they can focus on a single number to identify uninhabitable conditions.

The heat index is an estimate you might see in a weather report; it takes into account heat and humidity to represent the feeling of the weather. The wet bulb temperature is actually the temperature measured by a thermometer wrapped in a damp cloth. (Technically, the temperature in the forecast is the dry bulb temperature because it is measured with a dry thermometer.) The wet bulb temperature can estimate what your skin temperature will be if you sweat a lot, so it is usually used to approximate How would people fare under extreme heat.

The wet bulb temperature around 35 °C or 95 °F is almost the absolute limit of human tolerance, said Zach Schrader, A physiologist at Indiana University Bloomington. In addition, your body will not be able to effectively dissipate heat to the environment to maintain its core temperature. This does not mean that the high temperature will kill you immediately, but if you cannot cool down quickly, your brain and organs will begin to damage.

This Adapt This can cause a large change in the wet bulb temperature of 95°F. In the absence of wind and sunny days, the wet bulb temperature in an area with a humidity of 50% will reach around 109 °F, which is not suitable for living. In most dry air, the temperature must be as high as 130 °F to reach this limit.