Deadly humid heat could hit billions, spread as far as US Midwest, study says

Subject: Geography

Section: Physical geography

Context:

Billions of people could struggle to survive in periods of deadly, humid heat within this century as temperatures rise, particularly in some of the world’s largest cities, from Delhi to Shanghai, according to research.

Research findings:

The world is on track for 2.8C (5F) of warming by the year 2100 under current policies, according to the 2022 United Nations Emissions Gap report.
It found that around 750 million people could experience one week per year of potentially deadly humid heat if temperatures rise 2 degrees Celsius (3.6 degrees Fahrenheit) above preindustrial levels.
At 3C (5.4F) of warming, more than 1.5 billion people would face such a threat.
Regions impacted are:
- While India, Pakistan and the Gulf already have briefly touched dangerous humid heat in recent years, the study found it will afflict major cities from Lagos, Nigeria, to Chicago, Illinois if the world keeps heating up.
- At 4C of warming, Hodeidah, Yemen, would see around 300 days per year of potentially unsurvivable humid heat.

Wet-bulb threshold:

To track such moist heat, scientists use a measurement known as “wet-bulb” temperature. This is taken by covering a thermometer with a water-soaked cloth.
The process of water evaporating from the cloth mirrors how the human body cools down with sweat.
In a 2010 study, Huber proposed that a wet-bulb temperature of 35C (95F) persisting for six or more hours could be the conservative limit for the human body. Beyond this, people were likely to succumb to heat stress if they could not find a way to cool down.
Later the researchers found the limit was lower at between 30C (86F) and 31C (88F).
The research also concludes that the geographic range and frequency of dangerous humid heat will increase rapidly under even moderate global warming.

Source: TH