The New Delhi heat was unrelenting this spring and summer. Day in and day out, the city woke up to a steamy sunrise and went to bed in sweltering darkness — the most persistent, widespread and severe heat event in India’s recorded history.

To better understand the toll such temperatures take on the nearly half of India’s workforce that toils outdoors, The Washington Post spent two of the hottest days in June following delivery driver Mohammad Hussain and bricklayer Ganesh Shaw as they labored in the broiling sun. Every 30 minutes, The Post measured the surrounding wet bulb globe temperature — an index of heat exposure that takes into account air temperature, humidity and the force of the sun’s radiation.

The men spent most of their days in conditions that would test even world-class athletes. Evening brought no relief; both returned to homes with no air conditioning, as is the case for three-quarters of the nation’s households.

Their experiences illuminate what a growing body of scientific literature is starting to show: Across India and around the world, summer has become a season of peril, when society’s poorest and most vulnerable members must live and work in conditions that push the limits of human endurance.

Given no choice but to work in the heat, Hussain and Shaw have found ways to cope. But if humanity does not drastically reduce planet-warming emissions, experts say, some places may become too hot for workers like them to make a living.

The Post followed Hussain from 8 a.m. to 7 p.m. on June 14 and Shaw from 10 a.m. to 9 p.m. on June 15 and measured the temperature metrics around both men throughout the days.

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Morning: 8 a.m.-noon

Just after 8 a.m., as workers and students file out of packed city buses and traffic starts to clog the city streets, Hussain pulls an orange Swiggy uniform over his head and swings a leg over his motorcycle.

For the next eight hours, as the mercury tops 105F the delivery man for one of India’s largest food and grocery apps will zigzag across South Delhi, delivering cold drinks, potato chips, boxes of fruit and 20-pound bags of wheat flour. The heat and humidity are a dangerous combination — so high that the human body cannot cool itself through sweating.

Greenhouse gas emissions, mostly from burning fossil fuels, are to blame for the extreme conditions, scientists say. Global average temperatures have increased more than 1.8 degrees Fahrenheit since the preindustrial era, prolonging periods of hot weather and boosting the chance of record-breaking events.

“We’re putting more energy into the climate system,” said Kristie Ebi, founding director of the Center for Health and the Global Environment at the University of Washington. “And one of the ways it’s coming out is these very extreme extremes.”

At its peak this spring, India’s heat wave affected nearly 70% of the country, with highs in some places pushing 113F. At least 90 people died across India and Pakistan, and thousands of farmers saw their crops destroyed.

A study by the World Weather Attribution network, which assesses how climate change contributes to extreme events, found that the Indian heat wave was made 30 times more likely by human greenhouse gas emissions.

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Hussain’s phone buzzes and the screen lights up: He has his first job for the day, delivering breakfast to a young engineer. The street is getting hotter and busier by the time he returns 40 minutes later for a quick breakfast snack. His friends offer him a bottle of water they froze overnight.

By 10 a.m., Shaw has already been working for about two hours.

A native of the poor state of Bihar, Shaw does construction, like millions of others from the northern Indian countryside who move to Delhi in search of a steady income. As India’s capital grows, it relies on a vast pool of informal laborers who bounce from site to site, knocking down homes and then rebuilding them.

They endure extreme heat and intense cold. For a day’s work, Shaw earns about $10.

“In our company, you start at 8 a.m. and end at 8 p.m.,” he said. “Whether it’s summer or winter, the work never stops.”

Given the intense sun, his body has a hard time protecting itself.

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His core temperature starts to rise, and tiny blood vessels just below his skin expand, redirecting blood away from his central organs and allowing for heat exchange with the surrounding air. His heart begins to pump harder to keep blood circulating, straining his cardiovascular system.

But this “dry heat exchange” isn’t sufficient to keep Shaw’s temperature in check. So he sweats.

Though the evaporation of sweat keeps Shaw’s body from overheating, it can have its own health costs if that water is not replaced.

Since early June, Shaw has felt dull pain in his lower abdomen whenever he bends over. A doctor said he might have a urinary tract infection or a kidney ailment. He prescribed Shaw ayurvedic medicine and told him to drink more water.

It would not be surprising if Shaw had developed kidney problems from his constant heat exposure, said physiologist Ollie Jay, director of the Heat and Health Research Incubator at the University of Sydney. Studies from Central America, Sri Lanka and India have revealed rising rates of chronic kidney disease going back to the 1970s. In many hot and humid regions, the problem has become so widespread it’s considered an epidemic.

“If you’re generating a lot of sweat, and not replenishing it, on a daily basis, then you’ve got a lot of problems,” Jay said.

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Afternoon: Noon-5 p.m.

The sun is beating down just after 1:30 p.m. as Hussain cruises down a broad boulevard called Africa Marg on his fifth delivery. He passes a crowd forming on the sidewalk. A water deliveryman has fainted and fallen off his motorcycle.

Hussain shakes his head.

For him, surviving the heat is about toughness. “He’s not mentally strong enough for work like this,” he said.

But experts say enduring extreme heat is more a question of what the body can physically bear. Even a young and healthy person such as Hussain can become overwhelmed in an environment like Delhi.

The higher the wet bulb globe temperature, the harder it is for people to keep their bodies cool, because sweat doesn’t evaporate as quickly in high humidity. Dehydration and low blood pressure can make people dizzy and delirious. Their kidneys and hearts must work harder. If their internal temperatures become critically high, toxic substances can leak from their guts into the bloodstream, triggering multiple organ failure, which can be lethal.

Jay, the physiologist, noted that the Australian Open has canceled matches when the wet bulb globe temperature exceeded 90.5F.

That number, he said, “is the threshold for elite, elite, highly conditioned athletes competing for millions of dollars for playing a sport.” He added: “And these guys [Hussain and Shaw] are supposed to stay in that just to do their jobs.”

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During the two days The Washington Post spent with Hussain and Shaw, both men dealt with wet bulb globe temperatures up to 92.8F.

The extreme conditions of the afternoon coincide with the busiest part of Hussain’s workday — when it becomes most difficult to stay hydrated.

He brings his own water to work each morning, but it usually runs out within a few hours. Hussain is also racing to complete enough deliveries to get a $5 cash bonus, leaving him no time to refill his water bottle.

The easiest way, Hussain says, is to ask his customers for water. But they are often in a hurry, or the request is too awkward.

On this day, an older woman in a luxury apartment won’t even interact with Hussain. She asks him to drop a bag of snacks outside her door before she opens it.

“With someone like her, you can’t ask for water,” he says as he takes the elevator back down.

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Across town the next day, Shaw sits on the cool marble floor of the home he’s working on and peers outside through the open facade. The four-bedroom apartments he’s building are worth $1.4 million each.

Delhi is so hot that architects often leave a “sapaat” — or hollow space — that allows hot air to flow out of the building, Shaw explains. But those efforts at cooling are undone by the enormous windows he will help to install.

In this part of ultrarich Delhi, residents don’t care. “They have air conditioners,” he said.

As a child growing up in rural Bihar, Shaw recalled, he would go cool off in the mango groves whenever it got hot. Delhi offers no such refuge because of a phenomenon known as the urban heat island effect.

The vast paved expanses of cities absorb and then re-emit the sun’s radiation. Heat bouncing off buildings amplifies the feeling of sunlight scorching the skin. Millions of vehicles, factories and air conditioners — most of them powered by fossil fuels — generate “waste heat” that adds to the overall burden.

Children cool off in the water park area at Jefferson Park in the Beacon Hill neighborhood of Seattle on Monday. Temperatures will be heating up as the week continues. A high of 88 is predicted for Thursday. (Ellen M. Banner / The Seattle Times)
Why some Seattle neighborhoods are hit harder by heat waves
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The problem is almost always worse in low-income areas. A 2019 study found that such neighborhoods in Delhi could be as much as 10.8F hotter than a wealthy neighborhood on the same night.

“Heat illness is a disease of vulnerability,” said emergency physician Cecilia Sorenson, director of the Global Consortium on Climate Health and Education at Columbia University. “Those who can protect themselves, do. And those who can’t, don’t.”

Like so much else about climate change, the toll of extreme heat is fundamentally unequal. It’s not just that wealthy people can more readily afford air conditioning, or that they are more likely to live in cooler neighborhoods with lush vegetation, less vehicle traffic and fewer factories. It’s that low-income countries are expected to experience far more dangerous conditions as the planet continues to warm.

In India, where the average citizen produces lower carbon emissions per year than are generated by a round-trip flight from New York to London, the number of extremely hot days is on track to triple in the next 30 years.

“That’s what keeps me up at night,” said Sorenson — imagining the death and devastation of today’s heat waves multiplied by 10, or 30 or 100. “We’re deeply underequipped to deal with what’s going to come.”

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Evening: 5 p.m.-9 p.m.

Hussain finishes work around 5 p.m. and rides home, but finds no respite there. The heat is worse inside than out on the densely packed streets of his working-class neighborhood, Khanpur.

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Because of a lack of ventilation and higher humidity indoors, wet bulb globe temperatures are higher in the small two-bedroom apartment that he shares with his wife, brother, sister and parents.

Researchers believe high temperatures at night compound the effects of a day spent roasting in the sun. People’s bodies are forced to work overtime to stay cool. Their sleep is disrupted. Their strained cardiovascular systems are denied a chance to recover.

It’s so hot on some nights, says Hussain’s mother, Sakeena Begum, that she can’t fall asleep until 4 a.m. Most days, she’ll take three baths to cool down. She often cooks only once, before 10 a.m., so the stove doesn’t heat up the house.

For years, the family has considered buying an air conditioner. But that would raise their electricity bill from about $25 to $40 a month, which they can’t afford. So they rely on two ceiling fans, spinning in futility.

“It’s ultimately a matter of money,” she said. “So there’s no point in thinking too much about it.”

It’s just as hot across town in Shaw’s home — a windowless, 6-by-9-foot concrete room without furniture or appliances.

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His two sons, ages 13 and 18, moved earlier this year to Delhi, where they are employed as cooks at a roadside lunch stall. Now the three live together deep in a warrenlike apartment building filled with migrant laborers.

After a day’s work, they struggle to cool down with two fans in their room. At 87.8F, the wet bulb global temperature inside the room would be near dangerous levels if they were working.

Before they sleep, Shaw’s younger son Beenu is again grumbling about Delhi — the crowds, the heat, the thought of another day’s work. His roadside lunch shack lacks fans, he complains, so he spends all day either at the stove or sweltering beneath a tree. His father responds stoically.

“A tree with shade,” Shaw said. “That is enough.”

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Gerry Shih and Anant Gupta reported from Delhi. Sarah Kaplan, Ruby Mellen and Anu Narayanswamy reported from Washington.