Surviving the Swelter: How Dangerous ‘Wet-Bulb’ Temperatures are Impacting the Eastern U.S.

This week, a severe heat wave is sweeping across the eastern U.S., affecting almost 170 million people. The National Weather Service (NWS) has issued heat warnings, while high humidity levels make it feel even hotter outside.

Heat and humidity together can be dangerous. Our bodies cool down by sweating, but when it’s humid, sweat doesn’t evaporate efficiently. This makes it tougher for our bodies to regulate temperature, increasing the risk of heat-related illnesses. Meteorologists often use the wet-bulb temperature to measure this heat stress. It’s a key factor in understanding how people may cope with rising temperatures due to climate change.

David Romps, a professor at UC Berkeley, explains the concept of wet-bulb temperature. It’s measured by using a wet sock on the end of a thermometer. This method helps gauge the cooling effect of evaporation. However, humans generate body heat, so we might feel warmer than the wet-bulb thermometer indicates. When wet-bulb temperatures rise near our body temperature of about 98.6°F (37°C), it’s hard for our bodies to cool off, which can lead to serious health risks.

Experts previously thought that a wet-bulb temperature of 95°F (35°C) marked the limit for human survival. But recent research challenges this. Kat Fisher, a Penn State PhD student, states that even a wet-bulb temperature of 87°F (30.6°C) at full humidity can be critical. If exposed for a long time, it may prevent our bodies from maintaining a stable core temperature.

To get a clear picture of heat stress, meteorologists use the wet-bulb globe temperature (WBGT), which considers air temperature, wind, cloud cover, and sunlight angle. Recently, WBGT values in the eastern U.S. hovered in the high 80s to low 90s Fahrenheit. Such extreme levels can cause heat stress in just 15 minutes for anyone working or exercising outside.

Climate change is making these dangerous heat conditions more common. Romps notes that human-induced warming is pushing wet-bulb temperatures higher, which can impact even healthy individuals. Research shows that areas like the Midwest may face critical wet-bulb temperatures regularly in the next few decades. NASA predicts that by 50 years from now, parts of Arkansas, Missouri, and Iowa could hit these dangerous levels.

Historically, our species has never encountered such extreme conditions. In fact, the U.S. is already facing significant heat-related deaths—around 2,000 annually, according to the CDC. Some experts believe that these numbers are likely underreported. As temperatures continue to rise, adapting our infrastructure and health systems becomes essential.

Understanding the limits of human endurance in extreme heat may be a matter of life or death. Addressing this issue urgently is crucial to safeguard public health in a warming world.

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Climate change,extreme heat,heat-related illness