Nawabshah, home to more than a million people, has the untidy, nondescript feel of just about any other small Pakistani city: tangled power lines, tacky roundabouts, squat buildings. It has one consistent claim to national fame, however: its dry, punishing heat, the suffering of which residents flaunt with pride and masochistic smugness. In 2018, the city even set the record for the hottest April temperature on the planet—122.4 degrees Fahrenheit. Ramzan, the owner of a little snack shop on the outskirts of the city, remembers that day: two students, addled by heat, went swimming in the canal next to his store and drowned.
I asked him what the hottest day on the planet felt like.
“Well,” Ramzan shrugged. “August was hotter.”
Ramzan had a point. Nawabshah often experiences temperatures as high as 127.4 degrees, but never in April—not that we know of, at least. A heat dome, an increasingly common meteorological phenomenon in which the atmosphere traps hot air like a lid or a bubble, caused the baleful 2018 record. Weather historians are quick to note that record-breaking events are, by definition, anomalies, but they are useful in determining whether the global climate is becoming more extreme.
A year later, on the eve of the record’s anniversary, the temperature in Nawabshah was a relatively mild 112.2 degrees. Still, the heat was interfering with life: Fighter jets at the local military base, on high alert because of escalating tensions with neighboring India, could not take off because the tarmac had melted and gone soft. Men rattled through the streets on motorcycles, their heads covered to provide some barrier against the sun, the ends of their scarves pressed daintily between their teeth to prevent the cloths from flying off. As a result, they appeared amusingly coy. Female polio vaccinators plowed from village to village, lugging ice chests full of liquid vaccine. They covered their faces, too, shielding themselves from scrutiny as much as from the sun: polio eradication is a risky, and occasionally deadly, endeavor in Pakistan, marred by propaganda and misinformation.
Samia, one of the vaccinators I met, measured how hot it was according to how many times a year she had to be hospitalized for dehydration or heat stroke. In 2018, she agreed, that number was definitely higher.
When meteorologists talk about record-breaking heat, they are referring only to the past two hundred and fifty years or so, as comprehensive global record keeping basically ceases prior to 1880. (If climate data is available for earlier years, it doesn’t cover enough of the planet to be considered accurate.) Nawabshah exemplifies these limitations: its meteorological observatory was established in 1953 and, given evidence of human settlement in the area from more than four thousand years ago, accounts for a mere sliver of local weather history. What were environmental conditions like three, four thousand years ago? Over the past decade, by drilling into the Arabian Sea and other inland locations, geologists have pieced together an ancient story, set in Nawabshah and the broader Indus basin: as the weather changed and rains abated, an entire way of life became a casualty of climate change.
Less than two miles away from where the boys dove to their deaths in the canal stood a single raised grave, draped in colorful cloth and withered rose garlands. It was three thousand years old, or perhaps four or five—Abdul Hameed, its caretaker, was not sure. For the past thirty years, Hameed had tended to the shrine over the grave daily, sweeping the ground, setting out water for birds, propping against the structure, magpie-like, whatever little trinkets he could find. In truth, the grave was likely only a few centuries old, but it lay next to the millennia-old remains of Chanhudaro, a major settlement of the Harappan civilization, which sprang up along the banks of the Indus River around the same time as the Egyptian and Mesopotamian empires arose farther west.
Hameed, heat-rumpled but gregarious, was brimming with stories. The shrine was now adjacent to an archaeological site. The archaeologists—whom he called goras (white), a slang term for foreigners—first came here in the 1930s, he said, but were forced to flee after a great fire-breathing creature emerged from a mound and scorched the entire excavated area. The goras who poke around the site now—in 2019, a French team of ten (six women, four men)—don’t go anywhere near that particular mound, he claimed. The team visits for a few months each winter, flanked by a contingent of local policemen, and leave before Nawabshah’s punishing heat sets in. Some of what they dig up is locked in a nearby bungalow. Before leaving, Hameed explained, they shovel the mud back into the site, making their intervention as unobtrusive as possible.
Beneath our feet, protective blue plastic peeked out from under a thin layer of dirt.
The Harappans were a cultured group: they developed a written language of symbols, made jewelry and art, and were among the first to wear red lipstick. Archaeologists and urban planners marvel at their cities, their immense water tanks, and their sewer systems. At one point in time, the Harappans constituted almost 10 percent of the world’s inhabitants. But around 3,800 years ago, their society began to crumble. Eight centuries later, for reasons that still largely elude researchers, it was gone.
When geologist Liviu Giosan began researching South Asia in the early 2000s, he was less interested in how the Harappan civilization ended than why it had emerged in the first place. Were it not for the water from the monsoons, the Indian subcontinent would have been a desert, just like the Sahara farther west. Although there are many monsoon systems around the world, the South Asian summer monsoon is the largest in scale and consequence. More than five thousand years ago, Giosan’s research shows, it was even greater: raging floods fed by rains washed over the Indus plains each year.
Around 4,500 years ago, as the monsoons weakened, the Harappans settled on the river valleys and took up inundation agriculture, relying on the diminished floods to soak the soil and replenish the groundwater. More than a thousand Harappan settlements have been dated to that period, located along hundreds of miles of the Indus and its five major tributaries. These impressively designed cities had populations that reached twenty thousand—immense for their time.
Then, Giosan’s research shows, the monsoons weakened even further.
“A delta is like a library,” Giosan explained to me over Skype in 2019. “It contains information about the hinterland.” As far as such archives go, the Indus delta is particularly well-preserved: the Arabian Sea floor off the coast of Pakistan is known for having very little oxygen, so that whatever lives or dies there is preserved for millennia.
This unique environment made it possible for Giosan’s team to collect marine sediment cores so comprehensive that they could analyze time periods as particular as twenty-five years, a high-resolution snapshot of ancient environmental conditions. They scrutinized the salinity levels in the shells of single-celled plankton preserved in the sediment to assess changes in rainfall. Fluctuations in salinity are a handy way of assessing how much water was carried into the delta, which in turn allowed the geologists to ascertain the amount of rainfall over time. In subsequent research, they were also able to determine how rain shifted from season to season: as the summer monsoon withered, the winter monsoon became stronger farther inland, near the foothills of the Himalayas.
When the Indus began flooding less frequently, and the gradual changes in precipitation became substantial, the Harappans scattered toward the mountains. Within a few hundred years, the earth had swallowed up their cities.
Most locals scrunched up their faces in confusion when I mentioned Chanhudaro. The fact that Nawabshah sat upon an important historical site from the Harappan era was not common local knowledge. Hameed knew of course, but when I brought up Giosan’s research about changing rain and flood patterns, he shook his head. The civilization collapsed not once but three times, he insisted—it flailed under the curse of a heartbroken princess whose father, the king of the land, thwarted her love affair. First, the city sank into the earth. Then the river swerved away in displeasure, leaving the lands parched. And on the final occasion, everything was turned on its head. When archaeologists dig up remains—pitchers, statues—they emerge upside down, he claimed.
For Hameed, my account didn’t carry sufficient cause. In his worldview, rivers swerved in anger or displeasure over human excess, the ground breathed fire, and the earth yawned open to swallow the world. In the heat of Chanhudaro, as we climbed the mound that supposedly had scared away its first excavators, I asked Hameed if we risked angering the creature that lurked beneath our feet. He shook his head. We were just exploring; we weren’t being extractive or exploitative. “The fire,” he said assuredly, “is for the greedy.”
Currently, Pakistan contributes less than 1 per cent of the world’s carbon emissions, but it’s among the ten countries that have, over the past twenty years, borne the harshest brunt of climate change. A 2020 study showed that if we continue on our current course, in fifty years a third of the world’s population will be living in areas as hot as the hottest parts of the Sahara, far outstripping the temperature range ideal for sustaining human life and agriculture. The glaciers that feed Pakistan’s rivers are melting, and rains are becoming increasing erratic and difficult to anticipate. Researchers studying monsoons in the last interglacial period, roughly 125,000 years ago, predict that the storms will become longer and more extreme as the earth continues to warm.
Giosan referred to the Harappans as a Goldilocks civilization: it only existed when conditions were just right. Did the Harappans know their way of life couldn’t last? Why didn’t they turn to canal irrigation, for instance? They traded extensively with the Mesopotamians, who had been digging canals for centuries. Perhaps the Indus River was not amenable to canal irrigation at the time—even thousands of years later, when the British set out to tame it with their steam and steel and gunpowder, they found themselves bewildered. (“A foul and perplexing river,” one grumpy lieutenant reported in 1833.)
It is also possible, Giosan reasoned, that the Harappans were unable to reach a consensus in time: irrigation systems require a degree of central control, and the cities of the Indus Valley, unlike most of the civilizations of their era, were quasi-democratic. “For me, this acts as a very powerful parable,” he told me over Skype two summers ago. The Harappans relied on a single resource—the annual Indus floods—to sustain their cities. For the moment, we rely almost exclusively on a single resource: fossil fuels.
When the Harappans abandoned their cities, they adopted a simpler, more scattered existence. “Which is not to say they didn’t have a life,” Giosan said. “Whether it was better or worse, perhaps that’s subjective.”
That day, in Nawabshah, formerly Chanhudaro, on the eve of the anniversary of the hottest April day on record, little boys sloshed and somersaulted in the shallow canal across the road from Ramzan’s shop. Their shalwars ballooned behind them, bobbing cartoonishly in the water. Farther away, in the relative privacy of the fields bordering Chanhudaro, where the canal split into progressively narrower branches, farm laborers soaked themselves in a narrow channel, taking a break from picking wheat. These women had traveled on foot from the Thar Desert, hundreds of miles away, just as they did every harvest season. Each year, as less water flows through the irrigation system that extends from the Indus, they must venture farther inland. Meanwhile, Pakistan’s carbon emissions, minuscule though they may be, are set to triple by 2030.
As the sun climbed the sky, the Thari laborers continued to pour water over their heads and wrung their dupattas in the canal. “Come,” they beckoned. “Swim with us.”