India Isn’t Ready for Deadly Combination of Heat and Humidityhttps://arstechnica.com/science/2022/06/india-isnt-ready-for-a-deadly-combination-of-heat-and-humidity/Recent heat wave has seen “wet-bulb” temperatures rise to potentially fatal levels
R Lakshmanan has been making steel frames in the southern Indian city of Chennai for 20 years. His job involves standing for long hours outdoors at construction sites, pounding screws with careful precision onto steel rods. Each day he makes nearly 600 frames, which end up becoming the skeleton of a home. Often he works 12-hour shifts, beginning at 6 am. He always feels fortunate when he gets to work under a shady tree.
But this year, that protection hasn’t been enough. Ever since temperatures in March hit a sizzling 38° Celsius—4° above normal for Chennai—the conditions have been stifling. The metal frames Lakshmanan works with have been too hot to touch, the steel burning his fingertips and leaving behind painful sores. He has seen construction workers, especially women, collapse around him, and has had to take breaks during the workday to cope with fits of dizziness and nausea. “On some days, there’s so much heat, it feels like you’re living in a fireball,” he says.
In India, high temperatures and humidity are increasingly combining to pose a deadly threat—one the country isn’t prepared for.
... When heat and humidity combine to push wet-bulb temperatures past 32° Celsius, physical exertion becomes dangerous. Consistent exposure to high wet-bulb temperatures—35° Celsius and above—can be fatal. At this point the sweating mechanism shuts down, leading to death in six hours.
On May 1, 2022, the wet-bulb temperature in Lakshmanan’s home city of Chennai hit 31° Celsius. The same day, the district of Ernakulam in the Indian state of Kerala recorded a wet-bulb temperature of 34.6° Celsius—a record high for the area.“Without the mechanism to rid the body of that excessive heat, there are many physiological changes that happen in quick succession,” says Vidhya Venugopal, a researcher in public health at the Sri Ramachandra Institute of Higher Education and Research in Chennai.
Raise your internal temperature by 3° to 4° Celsius, and you’ll start to struggle. “As the body tries hard to restore your core temperature, all other processes slowly grind to a halt,” Venugopal says. Blood vessels dilate and circulation slows, particularly to the extremities. Not enough blood will flow to the brain, affecting its functioning. You lose alertness, become drowsy, and don’t feel thirst anymore. Soon organs shut down, one by one. “When the brain stops giving messages to the heart, the pulse slows and the person goes into a coma,” she says.
“Humidity aggravates the killing power of heat,” says Ambarish Dutta, professor of epidemiology at the Indian Institute of Public Health in Bhubaneswar. “It can trigger catastrophic events like heart attacks and strokes, aggravate secondary conditions like diabetes, change the regulatory capacity of the kidneys, affect the endocrine system by triggering stress hormones. In short, it’s a silent killer.”
World Weather Attribution, an international collaboration that analyzes extreme weather events, estimates that India and Pakistan’s recent heat wave has led to at least 90 deaths across both countries. During India’s 2015 heat wave, wet-bulb temperatures in the southern state of Andhra Pradesh rose to 32° Celsius. That year, the heat killed over 2,500 people.
Such events are going to become increasingly common as climate change warms the world. What magnifies the problem is that as temperatures rise, so does the absolute humidity in the atmosphere, says Jane Baldwin, assistant professor in the Department of Earth System Science at the University of California, Irvine. Thanks to what’s known as the Clausius–Clapeyron relationship of thermodynamics, “for every 1° increase in temperature, you see a 7 percent increase in humidity,” she explains. It means that for countries like India, climate change has a compounding impact. The effect is strongest over the world’s oceans, and particularly the Indian Ocean, whose rapid warming is a big trigger of South Asia’s high wet-bulb temperatures.
... It’s also not just workers who need to take care when wet-bulb temperatures are high. Rising humidity and heat lift nighttime temperatures as well, which affects everyone. “When the humidity rises, the temperature doesn’t drop quite so fast at night,” says Steven Sherwood, a professor at the University of New South Wales Climate Change Research Center in Australia. When the sun goes down, infrared radiation disperses some of the heat that has built up on Earth during the day. “When humidity is higher, there is greater cloud cover, which acts like a blanket preventing that escape of heat,” he says.
At night the body should recover from the daytime assault of heat, but because nights are getting hotter, that recovery is hampered, says Dutta. Whenever people talk about the effects of heat, they usually refer to its direct effects—such as heat exhaustion and stroke, which can be fatal or debilitating—but these are only the tip of the iceberg, he says. “If heat stays high in the night, it affects the body’s homeostasis, its ability to regulate and maintain its internal body temperature.” Upset this and your cellular and metabolic activities become disrupted, which can be a driver of disease, and can even be fatal itself. This is a big concern, given that
only an estimated 8 percent of Indian households have access to air conditioning.Analysis by World Weather Attribution suggests that climate change has made deadly weather events in South Asia 30 times more likely than they used to be. In the pre-industrial age, extreme heat waves would crop up once every 3,000 years. Now the probability is once every 100 years. Across India, on average nine heat waves were recorded every year from 1980 to 1999. The average between 2000 and 2019 is almost triple that, at 23.
South Asia is also not the only area at risk. Potentially fatal mixtures of heat and humidity have been increasing around the globe. Coastal cities on the Persian Gulf seem particularly susceptible to very high wet-bulb temperatures in the future, says Luke Harrington, senior research fellow in climate science at the New Zealand Climate Change Research Institute.
According to data from NASA, other countries will experience more critical wet-bulb temperatures in the future too, including the United States. States such as Arkansas, Missouri, and even Iowa are at risk.
