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upstart writes in with an IRC submission for c0lo:

Global heating pushes tropical regions towards limits of human livability:

Humans’ ability to regulate their body heat is dependent upon the temperature and humidity of the surrounding air. We have a core body temperature that stays relatively stable at 37C (98.6F), while our skin is cooler to allow heat to flow away from the inner body. But should the wet-bulb temperature – a measure of air temperature and humidity – pass 35C, high skin temperature means the body is unable to cool itself, with potentially deadly consequences.

“If it is too humid our bodies can’t cool off by evaporating sweat – this is why humidity is important when we consider livability in a hot place,” said Yi Zhang, a Princeton University researcher who led the new study, published in Nature Geoscience. “High body core temperatures are dangerous or even lethal.”

The research team looked at various historical data and simulations to determine how wet-bulb temperature extremes will change as the planet continues to heat up, discovering that these extremes in the tropics increase at around the same rate as the tropical mean temperature.

[...] Dangerous conditions in the tropics will unfold even before the 1.5C threshold, however, with the paper warning that 1C of extreme wet-bulb temperature increase “could have adverse health impact equivalent to that of several degrees of temperature increase”. The world has already warmed by around 1.1C on average due to human activity and although governments vowed in the Paris climate agreement to hold temperatures to 1.5C, scientists have warned this limit could be breached within a decade.

This has potentially dire implications for a huge swathe of humanity. Around 40% of the world’s population currently lives in tropical countries, with this proportion set to expand to half of the global population by 2050 due to the large proportion of young people in region. The Princeton research was centered on latitudes found between 20 degrees north, a line that cuts through Mexico, Libya and India, to 20 degrees south, which goes through Brazil, Madagascar and the northern reaches of Australia.

Journal Reference:
Yi Zhang, Isaac Held, Stephan Fueglistaler. Projections of tropical heat stress constrained by atmospheric dynamics, Nature Geoscience (DOI: 10.1038/s41561-021-00695-3)

Original Submission