A heatwave-related post from 2023 has not aged well. Since 2023, each summer has had heatwaves of increasing intensity, duration and temperature. Despite what the MET office says, citizen weather stations have been recording wet-bulb temperatures (WBT) in Britain on days which are hot and overcast. This is deceptive because the heat during a wet-bulb event feels relatively harmless, but sweat can't evaporate because the atmosphere is saturated. This means the body can't cool purely through sweating. Exertion under these conditions can be lethal. The UK MOD has a mandatory policy for acclimatisation and exercise activity during wet-bulb event periods in the UK. They even stipulate the type of thermometer to measure the WBT, which has a built-in WBT Calculator so the measurer is not relying on tables. This was introduced following the deaths of soldiers on the Brecon Beacons during SAS selection in 2013. The post-mortem coupled with the "unusual" environmental conditions found that the men died from heat exhaustion.Moving underground, if the biosphere can survive, it might be an option.
I was actually camping during last August's 35°C days, and it was better to rest during the day, do stuff like move camp, etc. at night.
I grew up in the Middle East. Where deserts are sub zero at night and 40° in the day with next to zero humidity at 40° even the wildlife stays in the shade or underground. The problem we have in the UK is the addition of humidity this is where the wet bulb calculator is so important. 40°C with 50% relative humidity which was what occurred in Central England gave a wet-bulb output of 30.89°C. Wet-bulb temperatures above 30 °C (86 °F) pose potential fatal danger to humans outside. It's also very uncomfortable. In these conditions, you should avoid direct sunlight and drink lots of water.
The question is whether 50° is survivable without further emissions.
Why you need to worry about the ‘wet-bulb temperature’
Scientists think we need to pay attention to a measure of heat and humidity – and it’s edging closer to the limits of human survivabilitywww.theguardian.com
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A new study into human survivability: "A wet-bulb temperature of 35°C has been theorised to be the limit to human adaptability to extreme heat, a growing concern in the face of continued and predicted accelerated climate change. Although this theorised threshold is based on physiological principles, it has not been tested using empirical data. This study examined the critical wet-bulb temperature (Twb, crit) at which heat stress becomes uncompensable in young, healthy adults performing tasks at modest metabolic rates mimicking basic activities of daily life. Across six experimentally determined environmental limits, no subject’s Twb, crit reached the 35°C limit, and all means were significantly lower than the theoretical 35°C threshold." https://pmc.ncbi.nlm.nih.gov/articles/PMC8799385/
Most opinions I have come across among survivalists were surprised when informed that 35°C was theoretical and was not based on empirical data. "
The current 35 degrees Celsius wet-bulb temperature limit recommended for human survival is conservative as it doesn’t take into consideration individual variables or how humans live and work in the heat, according to new research led by the University of Sydney and Arizona State University.
The modelling study, published in Nature Communications, proposes a new human-centred physiological approach for assessing survivability and liveability in the heat.
The wet-bulb temperature limit for human survival indicates the maximum combinations of temperature and humidity that humans can tolerate without suffering inevitable heat stroke over a fixed duration of exposure.
“The idea is that you could survive for up to six hours at that level of heat exposure,” said first author Associate Professor Jennifer Vanos in the School of Sustainability at Arizona State University.
“That number really oversimplifies what happens physiologically in the body when your body is exposed to that temperature, and it doesn’t account for other important variables like age or other vulnerability factors.”
Associate Professor Vanos said the commonly used wet-bulb temperature for human survivability assumes the person is indoors or shaded, unclothed, completely sedentary, fully heat acclimatised and of an average size.
However, these assumptions do not align, in most cases, with how people navigate the summer months.
“One of the key takeaways here is that heat affects each person differently depending on individual factors. We know that some people are much more vulnerable than others, even in the same environmental conditions, simply due to their age, co-morbidities like heart disease or even their medications,” said Professor Jay.
“A key focus of the work we are doing here at the University of Sydney is on better understanding these differences from a physiological perspective, and giving people the tools and knowledge they need to make safe choices during extreme weather events.”
I am sure there are all sorts of people here who have survived far worse extremes or who will cite the now-banned Sauna Championships, or who grew up somewhere near the equator, etc. But they are not outdoor workers or currently living in the Global South, diabetics, or on antipsychotic medication, elderly, babies, pregnant or currently homeless.
From a Survivalism /Bushcraft perspective, a post about heatwaves that does not age well on a forum about outdoor skills it suggests a problem of understanding the issue. There are multiple new posts about anecdotal evidence for heatwave survival on here, but nothing I have seen cites real evidence-based information. Here is the link to the MODs policy on "Management of health and safety in defence - chapter 41: heat illness prevention" https://www.gov.uk/government/publications/management-of-health-and-safety-in-defence-arrangements-jsp-375-volume-1-chapter-41
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