Dust and Bones

In 2021, the bodies of 225 migrants attempting to reach the U.S. were recovered from the Arizona desert. This year, 126 bodies have already been found.

A third of these deaths are due to environmental exposures—like heat.

For the first time, a team of researchers has measured how exactly climate change will exacerbate migrant deaths along the border. Their findings should sound an alarm.

Dust and Bones

The impact of climate change on migrant deaths at the southwestern border


to grow sore. I’ve just gotten pricked by a piece of jumping cholla cactus—what some deem the Arizona desert’s most dangerous plant. My ankle is covered. I thought I was being careful but, clearly, not careful enough. In the desert, careful doesn’t cut it; you need to watch your every step. The sage-colored spines violently pierce into my skin: “Get them out, get them out,” I yelp to the group. The chollas leave behind a drop of blood and a lesson I won’t soon forget.

“Now, imagine the pain people feel when walking days in the desert,” said Adriana Carrillo, founder of migrant rescue group Save Our Souls Search and Rescue, speaking primarily in Spanish.

She drives from Los Angeles to Arizona with her group about twice a month to look for migrants who have gotten lost during their journeys to the U.S. She always hopes to find a living, breathing person she can save. Since she launched SOS Search and Rescue in December 2020, she’s saved 65 individuals, including a group of 20 migrants lost in the mountains. Most of the time, however, she’s searching for remains: bodies, bones, and belongings. So far, her team has recovered the remains of about 18 lost souls.

On this trip, Carrillo is in search of someone specific: Jesus Tomas Lobos.

We’ve been on foot for only two hours—steadily whacking away thick brush, sipping water, slowly baking under the sun—yet have another two hours to go. I remember that most migrants spend upwards of seven days walking through desert terrain before they reach this part of their journey in the U.S. Leading the group is Angel, one of Carrillo’s core team members who is withholding his last name out of safety concerns given the anti-immigrant opposition to his work. He knows the desert well and is always in front of the pack. He walks ahead with a yellow cross buckled into his backpack—there in case we find someone and need to mark a grave.

While I’m red in the face, Carrillo is, well, fine. In fact, she’s in her element. She’s 62 with a head of gray hair worn in a loose braid and a face whose expression alternates between worried and determined. She wears an electric green sunhat and a patterned scarf to protect her exposed neck. She walks with one hand on her hiking stick, made of a dead saguaro rib, and another on her radio. Her eyes always remain vigilant on her team.

Carrillo treads on the red desert rocks fearlessly. As I pant in silence, she sings and trills, invigorating our group of seven with much-needed energy. Her worn-out brown boots signal this isn’t her first rodeo. Carrillo has been making these trips for over five years, but she’s been exploring this particular region of the Arizona desert—some 20 miles northwest of Tucson—since September. That’s when Lobos first went missing. This trip marks her sixth time looking for him here where his family believes he was left behind. She’ll keep coming back until she finds him.

“It’s important to keep looking because so many brothers are lost,” she said. “When we find their remains, we know we can finally bring their family peace.”

Carrillo recites a prayer before we enter the desert. She always asks both God and Mother Earth for permission before entering—but she also prays for the lost souls like Lobos: “Father, we pray for all of our brothers here. We ask you to allow us to find the body of Jesus Tomas Lobos. Mama Pacha, we ask for permission to enter your lands. Guide us and lead us to our brother.”

Across the Southwest, at least 7,805 migrants have died between 1998 and 2019, according to U.S. Border Patrol data. Since 1990, over 3,600 deaths have occurred in the Arizona desert borderlands of Pima County where Carrillo works. In 2021, the number of annual deaths in the region reached a new high: 225. About a third of those deaths were caused by exposure to environmental extremes—like heat. This year may very well break 2021’s record. Already, 126 bodies have been found.

The border crisis is bad now, but climate change will make it exponentially worse.

While researchers have been investigating the way climate change will influence migration patterns for years, they have largely ignored the way climate change will affect the migration journeys themselves. Temperatures in the southwestern desert can already occasionally soar past 125 degrees Fahrenheit in peak summer months. By 2050, climate models project the state’s temperatures will leave much of the desert region uninhabitable.

“I worry about how many more migrant deaths we will have,” Carrillo said.

Now, for the first time, scientists have measured the impact a temperature rise from climate change will have on the bodies of people who walk through the Southwest. In a study published in Science in December, a multidisciplinary team of researchers found that global heating will likely result in more migrants dying along the U.S.-Mexico border. Atmos worked with the study authors to visualize their unique data set.

The study authors didn’t quantify how many more people will die. Instead, they looked at the way increased heat in this rough terrain will affect the physiological health of migrants, including pregnant women and children. To be more precise, they measured how much more water, on average, different demographics will need as the landscape takes its toll on their bodies. Dehydration is, ultimately, what kills many folks. As their bodies expel sweat to stay cool, they’re unable to replenish the lost water. The adult human is up to 60% water. Without it, the body ceases to function.

Across the Sonoran Desert, migrants leave behind water jugs painted black. They mistakenly believe the color will make the containers harder to spot. In actuality, it only makes the water warm up faster.

And those souls brave enough to cross the Arizona desert are well aware of this. They often walk with at least a gallon of water—that’s why black jugs litter the landscape—but one gallon (even two!) is hardly enough, as this study underscores. Back in Arizona, as I reach for my own bottled water to take a sip, I imagine what it would feel like to keep going without any water at all—to be unable to ease the maddening itch in my throat or the pounding in my head.

The thought makes me even more thirsty, and yet it’s a nightmare from which many migrants can’t awake.

was doing fieldwork with his students in the Arizona desert when he encountered a gruesome sight: the remains of Marisela Zhagui, a 31-year-old mother of three migrating from Ecuador. Her smuggler had abandoned her about four to five days prior. She probably died from hyperthermia; extreme heat is no joke.

A year later, her 15-year-old cousin disappeared six miles south of where De León discovered Zhagui. He got sick in the desert, so the smugglers left him behind, too. Unlike Zhagui, he’s never been found. He remains in the desert—his body reduced to dust, his bones buried beneath the sand. While death is devastating, De León said, it’s even worse when someone simply disappears without a trace.

Months later, De León was able to connect with Zhagui’s brother-in-law Luis Fernando Tenecora. He’s left with the guilt of her death. He urged her not to make the journey—he, himself, was sexually assaulted during his migration from Ecuador over 20 years ago. Still, he promised to help her once she arrived. That day never came, at least not how Tenecora imagined.

“We brought her here to hold her funeral and mourn,” he said in Spanish as we sat in his Queens apartment. “At least she got to come to New York in that way.”

Three years before he found Zhagui’s body, De León founded The Undocumented Migration Project, an organization dedicated to raising awareness of the immigration crisis the U.S. faces at its southern border. His organization works with families that are looking for loved ones. Most families are from Mexico, Honduras, Guatemala, and El Salvador. However, his team is finding more people migrating from elsewhere: Cuba, Venezuela, Costa Rica, Brazil, Ecuador, Haiti, West Africa, and even India.

De León is one of the authors of the Science study published in December, mainly conducting interviews and gathering qualitative information on the lived experiences of migrants who cross the border. “I’ve been saying for over a decade that extreme dehydration and exposure to the elements has killed thousands of migrants,” he said. “This study is just one additional way to quantify that and be able to demonstrate that we’re not making this stuff up.”

This is the sort of scientific response a public health crisis usually calls for—research to quantify and mitigate mortalities. We’ve seen a growing number of studies, for instance, on air pollution, its causes, and how to reduce it. Most recently, the COVID-19 pandemic illustrated the way governments can coordinate science-based action on a massive scale to save human lives.

“The longer you spend out in the desert, the more water you’re going to need to simply survive.”

Reena Walker
University of Idaho

Despite the towering death toll of migrants, there’s been little response from both government and researchers to adequately understand how to address the public health crisis migrants face when walking among the Southwest’s remote, cacti-covered borderlands. That’s why De León and seven other scientists came together to investigate not only how future temperatures may push the limits of the human body, but to also shed light on how officials can help prevent that altogether.

“We just found it astounding that there wasn’t a quantified measure of physiological stress to cross the border,” said study author Reena Walker, a Ph.D. candidate at the University of Idaho. “The goal of the study, really, was to bring quantified estimates of how difficult this terrain is to inform discussions about how to actually improve human health in the next century before the situation gets worse under climate change.”

The team found that, on average, the amount of water people will need to travel through the desert in 2050 will increase by 34.1%—or about a third more than what their bodies need now. In 2020, the average person needed 2.16 gallons to survive diurnal travel, or migration during the day. By 2050, they’ll need 2.77 gallons.

Those numbers shifted when the researchers zoomed into specific demographics, though. A 5-year-old child from Latin America needs the least water: 1.23 gallons in 2020 and 1.58 gallons in 2050. Meanwhile, an adult pregnant woman from Latin America needs the most: 2.84 gallons in 2020 and 3.6 gallons in 2050.

“We’re seeing a much more diverse set of people crossing the border and making the trek on foot, including families and children,” Walker said. “We know pregnant people do cross the border, and we do know as physiologists how incredibly taxing that is on the human body.”

These water amounts quantify what a person needs to survive—not what they’ll need to feel comfortable. And all of these estimates are conservative. That’s because the study assumes that these individuals are healthy. In real-life migrations, people may decide to cross even if they’re sick or have health issues. Often, people become sick or malnourished during the trip itself. They can’t travel with much and often have to rely on their smuggler for meals.

To conduct the study, the authors first mapped out potential migration paths between Nogales, Mexico, and Three Points, Arizona. This is a commonly traveled region for migrants. I walked throughout the desert right outside Three Points during my visit in May. There, I saw an endless array of what people leave behind: blister-soaked socks, disheveled blankets, and sunburnt backpacks.

Camouflage backpacks like these are scattered across the landscape. Inside, water bottles and foot powder show what migrants most urgently need during their journeys.

However, every migrant’s journey is different. The study authors tried to reflect that reality in their findings. In one route they mapped, the migration to Three Points is a straight shot, making it less intensive. In 20 others, the path is randomized. In all of them, a person only walks about 50 miles over two days. This is a critical limitation in the paper because it assumes a person is walking this distance and that they’re only spending 48 hours boiling beneath the sun.

“The longer you spend out in the desert,” Walker emphasized, “the more water you’re going to need to simply survive.”

The authors used six climate models to compare the study area’s summertime temperature in 2020 with what’s projected there in 2050 under a middle-of-the-road climate scenario where governments have taken some mitigation measures but not nearly as much as they should.

The researchers had to, then, feed all this data into another model that measures the cost of environmental changes on whatever species is inputted. They were looking at temperature, sure, but also wind speed, humidity, and cloud cover. Every species has its factors that influence the model, too: metabolism, skin properties, sweat rates. For humans, even the clothing someone wears must be included in the model. It also considers geography, such as terrain slope.

Ryan Long, a senior study author and associate professor of wildlife science at the University of Idaho, has used this model to explore how climate change affects elk. He’s seen a classmate use it similarly for grizzly bears. This was his first time, however, using it for humans. In fact, this was the first time any researcher used the biological model on their own species.

“You can only sweat so much before your body has to replace that water.”

Ryan Long
University of Idaho

Our species is unlike many of the other animals that frequent the Sonoran Desert. Some avoid the sun by burrowing. That’s true for cold-blooded reptiles like the poisonous Gila monster or the western diamondback rattlesnake, which rely on their environment to heat their bodies. When the desert grows painstakingly hot, they go underground to cool off. If they’re cold, they’ll lie on a rock in the sun. Even the adorable Harris’s antelope squirrel has evolved to survive the harsh temperatures: it uses its tail as an umbrella to shade itself.

Humans, on the other hand, have to rely on our own ingenuity to survive the desert. We’re endotherms, so our bodies are designed to maintain a constant internal temperature. When the temperature around us pushes our internal temperature too high or too low, our body starts to work. And that, well, comes with a cost.

We shiver when we’re cold to produce more heat. The cost there is energy. When we run out of energy, we can’t keep shivering to keep our bodies warm. We sweat when we’re hot to release heat. The cost there is water.

“You can only sweat so much before your body has to replace that water,” Long said.

There’s no overvaluing our physical need for water. It’s why many search and rescue groups along the border leave water behind. They know water is often the key to survival for migrants. During my trip in the desert with Carrillo, she kept insisting to the group that we should fill up the empty jugs scattered beneath trees with our water to leave some behind for others. The sun was too strong that day, so she ultimately decided against it. Under those temperatures, the water would be boiling by the time anyone found it. Plus, there’s always the risk that we’ll need the water for ourselves—or for a survivor we find along the path.

About three and a half hours into our rescue mission, a volunteer alerted the group that she wasn’t feeling well. She didn’t think she could make it much longer. We eventually took a long break beneath a tree, which protected us from the sun. I drank from an icy water bottle and distressingly chewed on some tuna and crackers. I was feeling exhausted and faint myself. Heat affects the brain, too, and I was struggling to concentrate on anything anyone was sharing with me. I was distracted by my thoughts. How long do we’ve got left? When will we reach a toilet? I didn’t think I could walk the remaining few miles.

While we sat there, Carrillo shared a sobering story. Many remains they find are often beneath trees. The shade offers migrants a final relief before they die. She recalled an instance last year when she found a corpse slumped against a tree not far from where we were sitting. This was only the second time she’s ever recovered a full body. The man (who had migrated from Guatemala) hadn’t been dead long, so his limbs and torso were still intact. The same can’t be said for his face, which the scavengers and sun had already gotten to.

As chilling as that story may sound, Carrillo never once considered ending her work. The stakes are way too high. She still finds survivors. They need her—and she needs to know she’s doing something to help. Without teams like hers, these migrants will be left to die. And as morbid as it is to find a body, at least that leaves families with someone to bury. It’s better than finding bones. Or, worse, finding nothing at all.

The search and rescue team always brings a yellow cross to mark a grave in case a body is found.

for her brother Jorge Alexander Elías Murcia since May 18, 2021. He was left abandoned near the Texas border, at least according to the last texts he sent Elías Murcia. His arrival to Los Angeles, where his sister lives, would’ve marked their first reunion in over 20 years.

“I had a lot of dreams to finally see him again,” Elías Murcia shares in Spanish, her voice breaking through tears. “Disgracefully, those dreams stayed there near the border, but I haven’t lost faith. I ask God to watch over him wherever he may be.”

She doesn’t know if her brother, who would be 46 now, is still alive. She regularly receives messages from extortionists who claim they have her brother—but they’ll help only if she pays them. She knows now these are lies, but it’s traumatizing to receive these messages.

Her mind is always racing. The morgues or hospitals haven’t found her brother, so Elías Murcia wonders if he’s still out there. Did a racist rancher find him and force him into enslavement? Perhaps the cartel took him hostage. She ponders over whether he’s alive, suffering, or if he’s really dead. She may never know. Unlike the Arizona border, which is largely made up of public lands by way of national parks and wildlife refuges, the Texas border is made up of miles upon miles of private land. That makes it nearly impossible for human rights groups to go in and conduct searches and rescues.

“I haven’t lost faith. I ask God to watch over him wherever he may be.”

Teodora del Carmen Elías Murcia
Sister of Lost Migrant

“They can’t do searches because Texas is anti-immigrant, and the ranchers don’t allow them on their land,” said Elías Murcia, who’s asked several groups with the hopes of them finding her brother.

The number of deaths at the border is an underestimate. These numbers only mark the deaths that officials can confirm—the bodies they’ve found. Many migrants disappear forever, the question of their death always lingering. It’s the not knowing that drives people mad. It’s why Carrillo won’t stop traveling to the Arizona desert. She knows the feeling herself.

More than 30 years ago, her cousin died crossing the border. She waited 15 days before authorities found his body. The desperation and pain she felt during those 15 days have never left her. Angel joined the searches after his wife encouraged him to. One of her brothers got lost during his migration; luckily, someone found him, so he survived. The same can’t be said for countless others.

As I struggled to keep up with Carrillo and Angel during our five-hour search in May, my mind kept coming back to my loved ones who have navigated this desert landscape, too. There was my mom, who prefers not to speak of her trip north. When she has, she’s told me of the single night she hid in the desert brush—and how chilled the air felt. That was the first time my mom ever experienced the cold. In the desert, I’d put one foot in front of the other, imagining how tired my mom must’ve felt then. She was only 17 and had worked since she was 10. She didn’t even want to come to the U.S.—she had a boyfriend she adored, a best friend she loved, a life she cherished—but her family needed her to.

The desert artifacts offer a glimpse of a migrant’s journey. There’s the soda to quench thirst, the pants that are removed as the heat becomes unbearable, and the batteries that power flashlights. Every artifact carries a story.

As we would stop to examine the desert artifacts people left behind, I couldn’t shake the shock I felt even though I knew the stories. We’d find socks and shoes strewn about with bottles of foot powder nearby. I saw all this and thought of my tía, the only one of my mom’s four sisters to migrate here, too. I remember when I drove us to pick her up after she finally arrived in New York after weeks of travel. When she got in the car, one of the first things she said was how sorely her feet hurt—that they were covered in blisters, every one of her toenails gone.

My mother migrated here decades ago before the U.S.-Mexico border grew so militarized, pushing migrants into more remote and treacherous territory. My tía came during the Donald Trump era. Every year, however, the journey north grows more dangerous. Immigration policy (or lack thereof) leaves officials overwhelmed by the humanitarian need. The heating climate makes everything worse. With every year that passes, the temperatures climb. And until world leaders reduce greenhouse gas emissions, temperatures will continue to climb. The result will be more deaths.

The desert is full of spirits lost—but not even they can protect their kin from what the arid land holds. As I walked the same path where many lives have ended, pages of the Bible lay scattered in the dirt. Their words were barely legible, burnt away by the sun. I wondered: can God save the migrants who dare take this journey? We know water can, but there’s only so much a person can carry—especially when they’re being hunted by a government that not only wants the desert to claim them but is counting on it.


Correction, August 31, 2022 11:43 am ET
The story has been updated to correct the name of Luis Fernando Tenecora, which was previously written as Luis Armando Tenecora. The story also has been updated to clarify the circumstances of the death of Marisela Zhagui. She likely died from the heat, not the cold. The timeline for the founding of The Undocumented Migration Project has also been updated.


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