How long can humans survive in a climate of deadly heatwaves?
Some places on earth have already reached the limits of human tolerance for short periods of time. Scientists say it will get worse.
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In 2017, a team of climate scientists at the Lamont-Doherty Earth Observatory at Columbia University in New York published a study that contained these prescient words:
In the coming decades heat stress may prove to be one of the most widely experienced and directly dangerous aspects of climate change, posing a severe threat to human health, energy infrastructure, and outdoor activities ranging from agricultural production to military training.
In the wake of the extreme temperatures that scorched the Pacific Northwest in late June and led to several hundred “excess” deaths in Oregon, Washington State and Canada, as well as the increasing frequency and magnitude of extreme weather events globally, it may be time to ask a rude question: Is the planet becoming uninhabitable for humans?
On that scary question, the colleagues published a new, even more alarming study in 2020 called “The emergence of heat and humidity too severe for human tolerance” (links to both studies below) that found that combinations of heat and humidity exceeding the limits of human endurance would begin popping up in various regions in this decade. (This has already happened for brief periods in areas of Pakistan and Dubai.) The report addresses the question of survivability:
While some heat-humidity impacts can be avoided through acclimation and behavioral adaptation, there exists an upper limit for survivability under sustained exposure, even with idealized conditions of perfect health, total inactivity, full shade, absence of clothing, and unlimited drinking water. A normal internal human body temperature of 36.8° ± 0.5°C requires skin temperatures of around 35°C to maintain a gradient directing heat outward from the core. Once the air (dry-bulb) temperature rises above this threshold, metabolic heat can only be shed via sweat-based latent cooling, and at TW (wet bulb) exceeding about 35°C, this cooling mechanism loses its effectiveness altogether.
A key variable in surviving extremely high heat is the amount of humidity in the air. Humidity reduces the evaporation of sweat, the body’s natural way to shed heat, which is why TW (wet bulb) measurements are vital. Dry heat is less deadly (although it can still kill and sicken) than humid heat. The National Oceanic and Atmospheric Administration (NOAA) on Friday confirmed that last month was the hottest June ever recorded in 127 years of tracking temperatures in the U.S.
There are some glimmers of hope from a 2021 study by Princeton researchers Yi Zhang, along with two other Princeton researchers, Isaac Held and Stephan Fueglistaler which found TW is controlled by established atmospheric dynamics and thus can be “robustly” projected on regional scales. If the wet-bulb temperature in the tropics can consistently increase by only 1 degree Celsius with every degree of mean warming (compared to the past 40 years), it’s likely that heat and humidity in a large portion of the tropics will stay within habitable levels. The study is clear that a lot more research needs to be done on health impacts.
The Columbia and Princeton researchers are not the only scientists sounding the alarm. According to a 4,000-page Intergovernmental Panel on Climate Change (IPCC) report, obtained exclusively by Agence France-Presse (AFP) before its scheduled release in February 2022 and summarized in an article in Phys.org on June 23 :
If the world warms by 1.5 degrees Celsius—0.4 degrees above today's level—14 percent of the population will be exposed to severe heatwaves at least once every five years, "a significant increase in heatwave magnitude,“, the report says.
One thing that seems clear is that previous climate models that suggested the anthropogenic heatwave surge was decades off were wrong. From the “human tolerance” report:
Our findings indicate that reported occurrences of extreme TW have increased rapidly at weather stations and in reanalysis data over the last four decades and that parts of the subtropics are very close to the 35°C survivability limit, which has likely already been reached over both sea and land. These trends highlight the magnitude of the changes that have taken place as a result of the global warming to date. At the spatial scale of reanalysis, we project that TW will regularly exceed 35°C at land grid points with less than 2.5°C of warming since preindustrial—a level that may be reached in the next several decades.
Clearly, we are at a tipping point in which the real-world consequences of 300 years of pumping greenhouse gases into our atmosphere are becoming deadlier, more frequent and more visible to anyone who pays attention. Given our struggles to get vulnerable humans to get themselves vaccinated against a potentially fatal disease like Covid, it’s hard to be optimistic that there are enough persuadable people to answer the call in time. Maybe we could start a QAnon rumor that all those UFOs we’ve been hearing about are really scouting missions from some “socialist” planet whose atmosphere is getting too cold for survival looking for a warmer place to live after we’re gone. It’s us or them, Jim Dandy.
Dig Deeper
Temperature and humidity based projections of a rapid rise in global heat stress exposure during the 21st century (Environmental Research Letters)
The emergence of heat and humidity too severe for human tolerance (Science Advances)
After COVID, could the next big killer be heatwaves? (Phys.org)
Projections of tropical heat stress constrained by atmospheric dynamics (Nature Geoscience)
Will 'extreme weather attribution' become the next cultural wars bogeyman? EarthWatch)
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