Wet-Bulb Temperature

This is the key part:<p>&gt; A sustained wet-bulb temperature exceeding 35 °C (95 °F) is likely to be fatal even to fit and healthy people, unclothed in the shade next to a fan; at this temperature human bodies switch from shedding heat to the environment, to gaining heat from it.<p>The important thing is that passive&#x2F;evaporative cooling simply stops working. In fact, sitting in front of a fan would actually speed up your death. You&#x27;ll also die shockingly quickly (20 or so minutes, even for healthy, fit adults).<p>The only thing that can save you is:<p>- air conditioning<p>- getting in a cold tub<p>- going somewhere cooler (obviously) like a basement or parking structure<p>There are two thing that make this frightening:<p>1. We have already, for the first time in history, started seeing spikes of wet-bulb temperatures that exceed these values. Fortunately so far they have been in uninhabited areas.<p>2. If we ever see these temperatures in a city, odds are that the electrical grid would fail on account of the strain by A&#x2F;C units.<p>So picture this: a heat wave of this magnitude hits a large city. Bangkok, Phoenix, Melbourne. It lasts for 48+ hours. The grid fails on account of the strain. We&#x27;re looking at a mass casualty event with millions of dead in a matter of hours&#x2F;days.

For a harrowing depiction of what sustained wet-bulb temperatures could look like, check out the opening of Kim Stanley Robinson’s <i>Ministry for the Future.</i>

This doesn&#x27;t seem to be mentioned in the article, but an important related concept is delta-t, which is the dry-bulb temperature minus the wet-bulb temperature. It varies roughly inversely with relative humidity.<p>It&#x27;s a particularly important metric for farmers&#x2F;growers who use pesticide spray, as it influences the way the spray behaves when released from the applicator.<p>If the delta-t is too high, the spray droplets will evaporate too fast, before they land on the plant. Whereas if it&#x27;s too low, it can remain in droplet form for too long, which can reduce plant uptake, and in combination with other factors (particularly thermal inversions and wind) can lead to spray drift onto other crops, which can be hugely damaging.<p><a href="https:&#x2F;&#x2F;www.cropsmart.com.au&#x2F;using-delta-t-for-assessing-spray-conditions&#x2F;" rel="nofollow">https:&#x2F;&#x2F;www.cropsmart.com.au&#x2F;using-delta-t-for-assessing-spr...</a>

Dew point is another measure I like. I find the commonly reported form of humidity (relative humidity) to be the least useful.<p>Growing up, when the dew point hit 70, I knew it was going to be a miserable day, even if the relative humidity wasn&#x27;t as high as other days (where the relative humidity was quite high because of a storm moving through)

I think the claim &quot;Even heat-adapted people cannot carry out normal outdoor activities past a wet-bulb temperature of 32 °C (90 °F)&quot; is dubious.<p>When I lived in Taipei, it would common to have 100F @ 100% RH in July&#x2F;August and life&#x2F;activity didn&#x27;t suddenly stop because of it including people working outdoors. Now they may have modulated or changed how they worked outdoors but it&#x27;s not absolutely so dire as this line claims. The reality of seeing that is self-evident proof is wrong. I&#x27;m wondering where this actually cites from...

Obligatory psychrometric chart: [0]. I find it easier to understand how it&#x27;s all interrelated using a chart.<p>[0]: <a href="https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Psychrometrics#Psychrometric_charts" rel="nofollow">https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Psychrometrics#Psychrometric_c...</a>

This reminds me of swamp cooling. When I describe swamp cooling (evaporative cooling) to somebody who didn&#x27;t grow up with it, it blows their mind.

I&#x27;m not sure of that.<p>If you wet your body (or clothes) and sit in front if a fan (or in the wind of there is some) you will cool down.<p>Why? The fastest molecules tend to jump out of the surface of the liquid water. The wind push them away. So the wind removes the hottest molecules. That&#x27;s why you are cooler when it&#x27;s windy.<p>This mechanism works at any temperature.<p>Am I wrong?

Reminds me of my Army days using the Wet Bulb device to obtain the &quot;Flag&quot; status.<p>Used a dry bulb, wet bulb, and a black bulb fed into a slide rule calculator to determine the heat index and thus working conditions.<p><a href="http:&#x2F;&#x2F;www.wetglobe.com&#x2F;" rel="nofollow">http:&#x2F;&#x2F;www.wetglobe.com&#x2F;</a>

Hi Everyone,<p>I am a researcher that studies the interface between human heat stress and climate change. I list some news articles I was involved in and some peer reviewed manuscripts I coauthored below.<p>Tw at ~35°C (95°F), what does this mean? Putting it terms that may be more relatable, like the NWS Heat Index: whether at low or high relative humidity, a 95°F Tw is ~160°F Heat Index. A Finnish sauna (dry) temperature is ~160-190°F. However, a steam sauna is usually between 90-120°F, aka Tw of 90-120°F. Generally, you do not want to be in a steam sauna for more than 20 minutes, because it will very likely kill you. But, you do sweat a lot, and that can be quite relaxing, for short periods of time.<p>Tw 35°C is extremely rare in the outdoor environment. Persian Gulf&#x2F;Pakistan area, if they occur (the veracity of those measurements are difficult to confirm). What happens more often (although, still quite rare) is Tw of 32°C (89.6°F). Heat waves, such as the Chicago 1995 (&gt;700 dead) or the Indian-Paksitan Heatwave of 2015 (&gt;2500 dead) peaked at those temperatures. Humans cease being able to function&#x2F;perform labor at 32°C (89.6°F) Tw, regardless of the air temperature or humidity. And this is the real concern we have a climate scientists. Wet bulb temperatures peaking for extended periods of time (&gt;6 hours) rarely exceed 28°C (82.4°F) today.<p>But, the major work that’s come out recently (some of it mine, but is also verified by independent statisticians), is that global maximum Tw is tied to global mean surface temperatures, and scales readily with global mean changes. In the tropics, this change is reliably projected to be ~0.9°C (1.6°F) Tw per 1°C (1.8°F) of global warming.<p>So, you can do thought experiments. At what point of global warming will there be sustained (&gt;6 hours) of Tw at 32°C (89.6°F)?<p>Current max Tw at &gt;6 hours is 28°C in the tropics: Y = m<i>x +b b = 28°C (today) Y = 32°C (future) m = 0.9°CTw &#x2F; 1°C global T change x = (Y - b) &#x2F; m X = ~4.4°C global T change.<p>32°C (future) = (0.9°CTw &#x2F; 1°C global T change) </i> 4.4°C global T change + 28°C (today)<p>4.4°C change in global temperature is equivalent to ~8°F of global change.<p>This is a <i>lot</i> of global warming. But, not unlikely, given our current trajectories. Our estimate of global change by 2100 is about +4°C (7.2°F).<p>Cheers, -Jonathan R. Buzan PhD Climate and Environmental Physics and Oeschger Centre for Climate Change Research University of Bern, Switzerland<p>Some News Articles: <a href="https:&#x2F;&#x2F;www.bbc.com&#x2F;sport&#x2F;olympics&#x2F;57904094" rel="nofollow">https:&#x2F;&#x2F;www.bbc.com&#x2F;sport&#x2F;olympics&#x2F;57904094</a><p><a href="https:&#x2F;&#x2F;www.theverge.com&#x2F;2017&#x2F;9&#x2F;14&#x2F;16290934&#x2F;india-air-conditioner-cooler-design-climate-change-cept-symphony" rel="nofollow">https:&#x2F;&#x2F;www.theverge.com&#x2F;2017&#x2F;9&#x2F;14&#x2F;16290934&#x2F;india-air-condit...</a><p><a href="https:&#x2F;&#x2F;www.nytimes.com&#x2F;2015&#x2F;06&#x2F;07&#x2F;opinion&#x2F;sunday&#x2F;the-deadly-combination-of-heat-and-humidity.html" rel="nofollow">https:&#x2F;&#x2F;www.nytimes.com&#x2F;2015&#x2F;06&#x2F;07&#x2F;opinion&#x2F;sunday&#x2F;the-deadly...</a><p>Some Peer review manuscripts: <a href="https:&#x2F;&#x2F;iopscience.iop.org&#x2F;article&#x2F;10.1088&#x2F;1748-9326&#x2F;abeb9f" rel="nofollow">https:&#x2F;&#x2F;iopscience.iop.org&#x2F;article&#x2F;10.1088&#x2F;1748-9326&#x2F;abeb9f</a><p><a href="https:&#x2F;&#x2F;www.annualreviews.org&#x2F;doi&#x2F;abs&#x2F;10.1146&#x2F;annurev-earth-053018-060100" rel="nofollow">https:&#x2F;&#x2F;www.annualreviews.org&#x2F;doi&#x2F;abs&#x2F;10.1146&#x2F;annurev-earth-...</a><p><a href="https:&#x2F;&#x2F;gmd.copernicus.org&#x2F;articles&#x2F;8&#x2F;151&#x2F;2015&#x2F;" rel="nofollow">https:&#x2F;&#x2F;gmd.copernicus.org&#x2F;articles&#x2F;8&#x2F;151&#x2F;2015&#x2F;</a>