Wet bulb: It's the heat and the humidity

The most important temperature you’ve never heard of [Quartz](%2F%2Fqz.com/1/01000189ffe3fd98-99dc3212-b369-4058-8b84-c50062dcff77-000000/pQZn3GnuGxzlHZnREMGOfe44JvL7CKc1pX5eXERSBDo=314) [A woman with brown skin and short black hair holds a pink umbrella to shade from the sun, while standing in a Roman square in front of a yellow building. ](%2F%2Fqz.com%2Femails%2Fquartz-obsession%2F1850742732%2Fwet-bulb-its-the-heat-and-the-humidity%2F/1/01000189ffe3fd98-99dc3212-b369-4058-8b84-c50062dcff77-000000/VdIyMmYgSW5M2-C4o2d1md0tZtHKx6KjnWyFZe6Dpmc=314) Photo: Reuters (Remo Casilli) It is the humidity Next time you find yourself in a conversation about extreme heat, try inserting the following line to mix things up: “Yeah, but have you heard about the wet bulb?” The wet bulb temperature is the measure a thermometer registers when a wet cloth at ambient air temperature is put over the bulb end of the thermometer. This [essentially mimics the way the human body cools itself](%2F%2Fwww.weather.gov%2Fnews%2F211009-WBGT/1/01000189ffe3fd98-99dc3212-b369-4058-8b84-c50062dcff77-000000/eMyM2LOhrHJf7XdI4mEmrw052z1lTQMdHsPKqDTRn5M=314) in humid conditions. Wet bulb will always be lower than the dry bulb temperature [unless there is 100% humidity](%2F%2Fwww.weather.gov%2Fsource%2Fzhu%2FZHU_Training_Page%2Fdefinitions%2Fdry_wet_bulb_definition%2Fdry_wet_bulb.html/1/01000189ffe3fd98-99dc3212-b369-4058-8b84-c50062dcff77-000000/NogE6ZgliJWymC1f34S1LR8JkTa06ZGB73DWyrMrUDo=314). Then dry bulb and wet bulb temperatures will be the same. This tells us how hot and humid the air is. If the air is saturated with moisture, there will be less evaporation and thus a higher wet bulb temperature. If it’s more arid, there will be more evaporation and a lower wet bulb temperature. Wet bulb, more than anything, is about survivability. It’s not just about what it feels like outside. It’s what the human body can bear. If the wet bulb temperature is too high, the human body can’t properly regulate itself by sweating, and can experience heat stroke and death. Even young, healthy individuals can meet this fate under the right, and increasingly more common, conditions. This isn’t a future human problem—it’s happening now. On July 16, 2023 an [extremely dangerous wet bulb temperature](%2F%2Fearthsky.org%2Fearth%2Fwet-bulb-temperature-explained-dangers%2F/1/01000189ffe3fd98-99dc3212-b369-4058-8b84-c50062dcff77-000000/KeCWX3gSmP-cgmv28lZmh-aURfJvx8foHKvKmaq3LLo=314) of 33.7°C (92.7°F) was recorded in Asaluyeh, Iran. So why aren’t we using this metric to inform our daily lives? Wipe your brow, take a sip of water, and get ready for some heat. By the digits [35°C (95°F):](%2F%2Fwww.ncbi.nlm.nih.gov%2Fpmc%2Farticles%2FPMC2906879%2F/1/01000189ffe3fd98-99dc3212-b369-4058-8b84-c50062dcff77-000000/FzTNDpuCIwD05rencuavlkQkrsKfD8KB0h1ZHrnnRYU=314) Wet bulb temperature that would be fatal to humans and animals, though studies are finding that may actually be lower (more on that below) [36.3°C (97.3°F):](%2F%2Fen.wikipedia.org%2Fwiki%2FWet-bulb_temperature/1/01000189ffe3fd98-99dc3212-b369-4058-8b84-c50062dcff77-000000/4aV_3MX6qhoVbOgWuWkw4UnccYMnom14tRodXSrZCfM=314)The highest-ever recorded wet bulb temperature on Earth, registered in Ras Al Khaimah City, UAE [70,000:](%2F%2Fpubmed.ncbi.nlm.nih.gov%2F18241810%2F/1/01000189ffe3fd98-99dc3212-b369-4058-8b84-c50062dcff77-000000/at5D4Wg9SohEe6IILEYdRYFk6nuMqm8OVSBWokTrrLc=314) People who died during Europe’s 2003 heatwave, when the wet bulb temperature [was no higher than 28°C (82.4°F)](%2F%2Fwww.washingtonpost.com%2Fbusiness%2Fenergy%2F2023%2F07%2F04%2Fexplainer-how-extreme-heat-and-high-wet-bulb-temperatures-kill-people%2F83bca63e-1ada-11ee-be41-a036f4b098ec_story.html/1/01000189ffe3fd98-99dc3212-b369-4058-8b84-c50062dcff77-000000/GFVaIUdnR_RYejm-UqB_zxd71E-BdgYmoHei31VoC7Y=314) [20 million:](%2F%2Fthespinoff.co.nz%2Fbooks%2F01-11-2020%2Fyou-do-not-want-to-know-what-wet-bulb-means/1/01000189ffe3fd98-99dc3212-b369-4058-8b84-c50062dcff77-000000/E64kC8Q3u3st4xwPb8rKe7BPOkyCO2dPDqqeYCg4p-0=314) Fictional deaths in Lucknow, India in a high-humidity heatwave in the opening of Kim Stanley Robinson’s 2021 novel The Ministry for the Future [40:](%2F%2Fclimate.nasa.gov%2Fexplore%2Fask-nasa-climate%2F3151%2Ftoo-hot-to-handle-how-climate-change-may-make-some-places-too-hot-to-live%2F/1/01000189ffe3fd98-99dc3212-b369-4058-8b84-c50062dcff77-000000/SLz1bwTYod1UcRefUL-dnwq2O1JQ5Ey_ZPxD_CsXPH4=314) Years it has taken for extreme levels of heat stress to double in the US Origin story Basic wet bulb training Back in the 1940s, US soldiers in basic training were getting seriously ill, and between 1942 and 1944, [198 even died](%2F%2Fwww.forbes.com%2Fsites%2Fmarshallshepherd%2F2019%2F08%2F14%2Fwet-bulb-globe-temperature-is-great-for-heat-warningswhy-dont-we-use-it%2F/1/01000189ffe3fd98-99dc3212-b369-4058-8b84-c50062dcff77-000000/ZicZk-A3Q3DJSiDvgSr8sNUD7d3itomDhhWlMTU3oDg=314). The culprit? Heat-related illnesses. To combat this, the wet bulb temperature metric was developed in the 1950s. Understanding when the combined air temperature and humidity was too dangerous for the human body drastically reduced instances of heat-related illness among soldiers during drills. A coinciding flag system (green is low, red is high) is still used today—take a look at [what the wet bulb temperature is like](%2F%2Feconet.climate.ncsu.edu%2Fwbgt%2F/1/01000189ffe3fd98-99dc3212-b369-4058-8b84-c50062dcff77-000000/LzA8W1DBGFcz_GlIDmkiOKitBGisHgYb3iTlaeKqMDk=314) in North Carolina, home to several military bases. Both dry and wet heat can be [dangerous for the body](%2F%2Fwww.wsj.com%2Farticles%2Fhigh-temperatures-affect-human-body-11658262757/1/01000189ffe3fd98-99dc3212-b369-4058-8b84-c50062dcff77-000000/mZUpAQimF8fB6ZACMNbLn7OOyiVj57kWdHazjgBIHds=314), which is constantly trying to stay at a temperature between 97°F (36.1°C) and around 99°F (37.2°C). In dry heat—think the desert or a non-steamy sauna—the body cools itself when sweat evaporates off the skin. Dehydration can be a danger with dry heat, but in many cases that can be managed by drinking water. Wet heat—think steam room—short-circuits the body’s cooling mechanism by making it much harder for sweat to evaporate and lower body temperature, since there’s so much moisture in the air. If the US military has been using wet bulb temperatures for decades to decide whether or not it’s safe to work outside, why hasn’t the system reached everyday use? One reason could be that wet bulb temperatures [are generally lower than](%2F%2Fwww.forbes.com%2Fsites%2Fmarshallshepherd%2F2019%2F08%2F14%2Fwet-bulb-globe-temperature-is-great-for-heat-warningswhy-dont-we-use-it%2F/2/01000189ffe3fd98-99dc3212-b369-4058-8b84-c50062dcff77-000000/c56K9v_Tj0VGZzidP2eYycLiMDKq3HzhQ3DidvTQHkg=314) the air temperature and heat index—they may not sound as bad as what the high temperature is or what the heat index is, giving a perception that things aren’t quite as dire as they are. That and, well, it’s a trickier concept to master than simple temperature, or heat index, which is already lodged in our brains. Quotable “Ordinary town in Uttar Pradesh, 6 AM. He looked at his phone: 38 degrees. In Fahrenheit that was—he tapped—103 degrees. Humidity about 35 percent. The combination was the thing. A few years ago it would have been among the hottest wet-bulb temperatures ever recorded. Now just a Wednesday morning.” —Excerpt from Kim Stanley Robinson’s [The Ministry for the Future](%2F%2Fwww.orbitbooks.net%2Forbit-excerpts%2Fthe-ministry-for-the-future%2F/1/01000189ffe3fd98-99dc3212-b369-4058-8b84-c50062dcff77-000000/_hLRJwz9wKiWbvPpnr6s5L7Bf5m92TfTca1AeKOdTaU=314) Pop quiz [A gold retriever mops its brow with a handkerchief while panting](%2F%2Fqz.com%2Femails%2Fquartz-obsession%2F1850742732%2Fwet-bulb-its-the-heat-and-the-humidity%2F/2/01000189ffe3fd98-99dc3212-b369-4058-8b84-c50062dcff77-000000/q0RYVQCPuSv96fYHxtWhAp7g3aQF_6LGQd2WBFx4loY=314) Gif: (Giphy) Which weather variable isn’t included in a wet bulb temperature calculation? A. Cloud cover B. Wind speed C. Sun angle D. Particle pollution You’ll find the answer to the quiz at the bottom of this email, where it’s always sweater weather. Department of jargon 📈 Air temperature: The degree of hotness or coldness of the air as measured by a scale, such as a Fahrenheit or Celsius thermometer. 😓 Heat index: A measure of what it really feels like outside to the human body, when considering air temperature and humidity in the shade. 🥵 Wet bulb temperature: A measure that also combines humidity and air temperature, but in the sun. To take it, a thermometer is wrapped in a wet towel. Evaporation will lower the temperature, and the point at which the temperature stops dropping is the wet bulb temp. Brief history [1612:](%2F%2Fwww.brannan.co.uk%2Fwho-invented-the-thermometer%2F/1/01000189ffe3fd98-99dc3212-b369-4058-8b84-c50062dcff77-000000/5BAL64P-P4ZsGhFOlGi__jTEyYZJUi1vtXlliCoXiDk=314) Italian physiologist Santorio Santorio invents the first air thermometer to measure temperature. [1880:](%2F%2Fearthobservatory.nasa.gov%2Fworld-of-change%2Fglobal-temperatures/1/01000189ffe3fd98-99dc3212-b369-4058-8b84-c50062dcff77-000000/gadRT-VJVRSnPY1AvofgJr4a9Z-kBqC_x2QK8NuMZR0=314) Global temperature recordkeeping begins. [1950s:](%2F%2Fwww.jsams.org%2Farticle%2FS1440-2440(07)00147-8%2Ffulltext/1/01000189ffe3fd98-99dc3212-b369-4058-8b84-c50062dcff77-000000/2CV9rm2t4Oz4z_8LK3wenfwUvQK3NTxboQ8FJmfYDOg=314) The wet bulb measure is first used to help control heat illness at training camps for the US Army and Marines. [1970s:](%2F%2Fwww.forbes.com%2Fsites%2Fmarshallshepherd%2F2019%2F08%2F14%2Fwet-bulb-globe-temperature-is-great-for-heat-warningswhy-dont-we-use-it%2F%3Fsh=5c843a40df25/1/01000189ffe3fd98-99dc3212-b369-4058-8b84-c50062dcff77-000000/9j5nXQdVvEMGRg6WISl88FS-ziZ0pzVKUbY1xGkY8C0=314) The National Oceanic and Atmospheric Administration develops the heat index. [2003:](%2F%2Farchive.ph%2F20160426151143%2Fhttps:%2F%2Fwww.washingtonpost.com%2Fnews%2Fcapital-weather-gang%2Fwp%2F2015%2F07%2F30%2Firan-city-hits-suffocating-heat-index-of-154-degrees-near-world-record%2F/1/01000189ffe3fd98-99dc3212-b369-4058-8b84-c50062dcff77-000000/pp12PLvidQkENW8yG7jzv-YZleTrNO7eMuawmEMg5cs=314) The highest heat index in the world is registered in Dhahran, Saudi Arabia, at 178°F (81°C)—and the wet bulb [reaches 35°C](%2F%2Fwww.wunderground.com%2Fcat6%2Fheat-and-humidity-near-the-survivability-threshold-its-already-happening%3Fcm_ven=hp-slot-2/1/01000189ffe3fd98-99dc3212-b369-4058-8b84-c50062dcff77-000000/16pfIXgAMFiT1xwz6_vZRmlHhym399u1kZFKcB1XNsw=314). [2016:](%2F%2Fwww.bloomberg.com%2Fnews%2Farticles%2F2023-07-17%2F2023-is-already-on-track-to-be-the-hottest-year-ever-recorded/1/01000189ffe3fd98-99dc3212-b369-4058-8b84-c50062dcff77-000000/IzcyEQU0n3a-_iXRgiH4wgsUnJhMrW2gh8e-Ax2q2Gc=314) The warmest year on record is recorded (although it holds a close tie with 2020). [2023:](%2F%2Fwww.bloomberg.com%2Fnews%2Farticles%2F2023-07-17%2F2023-is-already-on-track-to-be-the-hottest-year-ever-recorded/2/01000189ffe3fd98-99dc3212-b369-4058-8b84-c50062dcff77-000000/3VSAonME-SU3kBqexRgTaQF4Rt7V8_sV1qG2YNyyO-c=314) The new warmest year is on its way to the record books. Fun fact! Galileo Galilei was the first person to invent a device that gauged heat in the early 16th century. But his thermoscope, as it’s called, was missing [a crucial piece](%2F%2Ftime.com%2F6053214%2Fthermometer-history%2F/1/01000189ffe3fd98-99dc3212-b369-4058-8b84-c50062dcff77-000000/BEr82i9wXw7DD98PmUwloqJgJKyiZdqc7TdLKfMnSSk=314) that differentiated it from the thermometer: a scale. It could show that temperature had changed, but not by how much. Take me down this 🥵 hole! The PSU H.E.A.T. Project As the global climate continues to warm because of human-induced climate change, the question of “how hot is too hot?” is one that scientists are spending more time studying. In 2021, researchers with the Noll Laboratory at Pennsylvania State University brought in young, healthy adults (thank you for your service) and put their bodies under heat stress in a controlled environment. Each swallowed a telemetry pill, [a tiny device](%2F%2Fwww.nasa.gov%2Ftopics%2Fnasalife%2Fthermometer_pill.html/1/01000189ffe3fd98-99dc3212-b369-4058-8b84-c50062dcff77-000000/iJf_Jd9qK3LIs-es58QtHyAK3EKZDJfjbnyUmpDTh0A=314) that can monitor core temperatures within the body. [What they found was stark](%2F%2Fjournals.physiology.org%2Fdoi%2Ffull%2F10.1152%2Fjapplphysiol.00738.2021/1/01000189ffe3fd98-99dc3212-b369-4058-8b84-c50062dcff77-000000/9a9qqmxWC233y-Yh0O7Z-Qz8LuZNNB-M1DqEOB123Tc=314). In both dry and humid climates, the deadly wet bulb threshold is likely significantly lower than 35°C. It’s closer to 31°C (87°F) when relative humidity is above 50%. (It’s not just humans—extreme wet bulb temperatures [can be deadly to animals](%2F%2Fthebulletin.org%2F2022%2F07%2Fextreme-heat-animals-livestock-wildlife%2F/1/01000189ffe3fd98-99dc3212-b369-4058-8b84-c50062dcff77-000000/NpySx2tcdFF6nsy2S_Miu_OjcMEB5wcUEDLU-ElKDfg=314), too). “The theoretical 35°C wet-bulb temperature threshold does not hold up under experimental testing,” the authors concluded, and “there is likely not one critical threshold that can be set, especially so in lower-humidity environments.” Poll [Meryl Streep stands in an office wearing a red blazer. ](%2F%2Fqz.com%2Femails%2Fquartz-obsession%2F1850742732%2Fwet-bulb-its-the-heat-and-the-humidity%2F/3/01000189ffe3fd98-99dc3212-b369-4058-8b84-c50062dcff77-000000/bmSfGP8_-AtEfTyfZNQSdGyUtV4jkrNgU2eN8l29ObM=314) Gif: (Giphy) How do you plan to ride out the climate crisis? - I can’t - Nobody can - In an underground bunker [Tell us your response](%2F%2Fwww.surveymonkey.com%2Fr%2FL3SCNGG/1/01000189ffe3fd98-99dc3212-b369-4058-8b84-c50062dcff77-000000/o7dwwjpEYR3GaWlwCKbWYRKliGaVGxUpDdItxT93gkQ=314), and we will find some way to incorporate a wet cloth into our analysis of the results. 💬Let’s talk! In our last poll about [market makers](%2F%2Fqz.com%2Femails%2Fquartz-obsession%2F1850729564%2Fmarket-makers-nudging-the-invisible-hand/1/01000189ffe3fd98-99dc3212-b369-4058-8b84-c50062dcff77-000000/LadkrI7pQXVlF0UlI6YekeRGdYm2aMxGfkhbFhkGxX4=314), we asked if you ever wondered if it’s become too easy to trade financial assets. 57% of you said yes, 38% of you said yes (but only for other people), and the rest of you said no, you own a Bloomberg Terminal. Which, wow! Also, we’ve corrected [the web version of that email](%2F%2Fqz.com%2Femails%2Fquartz-obsession%2F1850729564%2Fmarket-makers-nudging-the-invisible-hand/2/01000189ffe3fd98-99dc3212-b369-4058-8b84-c50062dcff77-000000/jvpCni7yvHttgFuGkZMjEddo00fmZOKeE9XZjoS0xQQ=314) to report accurate revenue data from Citadel during 2022; the original piece used data from the first half of 2023. The piece has also been updated to reflect the latest assessment of Citadel’s share of US equity market trading. 🐤 [Tweet (or X?) this!](%2F%2Ftwitter.com%2Fintent%2Ftweet%3Furl=https%253A%252F%252Fqz.com%252F1850742732%26via=qz%2520obsession%26text=Wet%2520bulb%253A%2520It%2527s%2520the%2520heat%2520and%2520the%2520humidity/1/01000189ffe3fd98-99dc3212-b369-4058-8b84-c50062dcff77-000000/rRRqRVhJIiCfGqu2psvDxX9GjdOLL0-10WxALIoLS5Q=314) 🤔 [What did you think of today’s email?](mailto:talk@qz.com?cc=&subject=Thoughts%20about%20wet%20bulb%20&body=) 💡 [What should we obsess over next?](mailto:talk@qz.com?cc=&subject=Obsess%20over%20this%20next.&body=) Today’s email was written by [Morgan Haefner](%2F%2Ftwitter.com%2Fmorgan_haefner%3Flang=en/1/01000189ffe3fd98-99dc3212-b369-4058-8b84-c50062dcff77-000000/wwCxLcLyGSOV53YDsoS7N-yl-3XssmC-RPaK4sP3m6k=314) (is now in the market for a portable wet bulb thermometer) and edited and produced by [Annaliese Griffin](%2F%2Fauthory.com%2FAnnalieseGriffin/1/01000189ffe3fd98-99dc3212-b369-4058-8b84-c50062dcff77-000000/Mu9aetjA3ihQcLuwLgUeVtaCZ4zdMNWH1gRR5DOZPuk=314) (wonders if emigration to Shetland is possible). The correct answer to the pop quiz is D., Particle pollution. Wet bulb temperatures [take into account](%2F%2Fwww.weather.gov%2Fict%2Fwbgt/1/01000189ffe3fd98-99dc3212-b369-4058-8b84-c50062dcff77-000000/LXnMGme2xBEjKA41LaZ3k3PtAQBAe_FeKuBnzvpBSfc=314) the temperature, humidity, wind speed, sun angle, cloud cover, and physical activity. [🌐 View or share this email online.](%2F%2Fqz.com%2Femails%2Fquartz-obsession%2F1850742732%2Fwet-bulb-its-the-heat-and-the-humidity%2F/4/01000189ffe3fd98-99dc3212-b369-4058-8b84-c50062dcff77-000000/-6CM3CYGdalUFhl1L3SLYvCmy8vhGj-4iXD4jtB0dpg=314) 1290 Avenue of the Americas, New York, NY 10104 © 2023 G/O Media Inc. [Unsubscribe](%2F%2Fqz.com%2Fnewsletter%2Funsubscribe%3FsubscriptionToken=4da3ee5afa774c51f11017f8d0e31196da52e648-115151%26utm_source=quartz_newsletter%26utm_medium=email%26utm_campaign=2023-08-16/1/01000189ffe3fd98-99dc3212-b369-4058-8b84-c50062dcff77-000000/Nds4wI1DPZco-0I7oA9riAgwAzobFmqvZgB9hyVCWyM=314)