As temperatures rise to new highs, not just in the Pacific Northwest but worldwide, you may hear the term “wet bulb globe temperature” used more frequently.
This somewhat ridiculous-sounding idea differs from phrases like perceived temperature, humidity index, and dew point in that it’s a little more sophisticated and more significant.
WBGT stands for wet-bulb globe temperature and is a more refined form of the heat index. It considers the temperature and humidity, wind speed, sun angle, and solar radiation levels (the heat index considers temperature and humidity and assumes you’ll be in the shade). The goal is to give people a better sense of how hot the weather feels rather than how hot the air is, and because it is more accurate to human perception than the heat index, more meteorologists have begun to use it.
Working in the sun for more than 30-45 minutes while the temperature is between 80 and 88 degrees Fahrenheit WBGT puts your body under a lot of stress. When the WBGT rises above 88, you can only work or exercise outside for 20 minutes without jeopardizing your health. You can’t stay active in the heat for more than 15 minutes if the temperature is over 90 degrees. When the temperature rises into the nineties, you should avoid going outside at all.
However, to truly comprehend WBGT, you must first understand the measurement’s primary component: wet-bulb temperature.
Wet-bulb temperature defines as the lowest temperature that a surface can attain in a specific spot through evaporative cooling (i.e., a wetted surface can reach with air passing over it).
That may sound a little esoteric but stick with us. The temperature of a wet-bulb is significant since it refers to how humans cannot keep themselves cool. Though they’re comparable, the heat index and apparent temperature aren’t the same. By adding information about the humidity and the observed air temperature, all of these measures aim to approximate how hot it feels outside. Because humans (and many other animals) cool themselves by allowing water to evaporate off of them, the more humid the air feels hotter. This occurrence is known as “sweat.”
Perspiration may be unpleasant, but it is a very efficient cooling system since water takes a long time to heat up. Your skin produces water, and as the droplets evaporate, they take some of your body heat with them. That is why “dry heat” is preferable to humid heat: dry air can absorb a lot of moisture, allowing sweat to evaporate more quickly. Perspiration allows your body to maintain 98.6 degrees Fahrenheit even when the temperature outside is much over 100 degrees Fahrenheit.
However, once the temperature of the wet-bulb reaches 95 degrees Fahrenheit, sweat stops operating. That’s because your skin has to be at or below 95 degrees to maintain a proper internal temperature. Wet-bulb temperatures beyond 95 degrees are particularly harmful since sweating is your skin’s mechanism for releasing heat. Wet-bulb temperature is the lowest temperature that a wet surface can reach through evaporation (read: sweaty skin can get). Skin temperatures that remain above 98 degrees for an extended period are deemed deadly.
For comparison, wet-bulb temperatures in Russia in 2010 and Europe in 2003 were below 83 degrees Fahrenheit. Approximately 55,000 and 35,000 individuals perished as a result of the heat waves.
That isn’t a case of merely refusing to exercise or work outside. If people do not have access to air conditioning or water, high wet-bulb temperatures can kill people who are simply sitting around doing nothing. Your body generates heat when it is at rest, and it requires a mechanism to get rid of it. If you don’t, the cellular systems that keep you alive stop operating. Your body is unable to cool itself when the temperature of the wet-bulb is too high.
Previously, it assumed that wet bulb temperatures on Earth rarely topped 91 degrees Fahrenheit. Still, a study published in the journal Science in 2020 discovered that this threshold had crossed numerous times. Multiple wet bulb temperatures above 95 have recorded already at two of the locations analyzed. According to the study, South Asia, the coastal Middle East, and coastal southern North America are among the locations that have already experienced high heat since they combine the humidity found near bodies of water with intense continental heat.
The National Weather Service publishes the wet bulb temperature for every place in the United States, so you may use this tool to find out what the current weather conditions are in your area. Extreme heatwaves, such as those that result in mass casualties, will only grow more regular. At moist bulb temperatures in the mid-80s and above, even healthy young people can die from heatstroke. Keep an eye on the forecast and make sure you’re aware of any warning indications.
Sara Chodosh is the author.