Thousands of people have died attempting to enter the U.S. from Mexico. And the crossing is growing even more dangerous as the climate changes.

U.S. border security policy in the Southwest is designed to deter unauthorized migration at heavily guarded urban entry points. So undocumented migrants with little access to water often spend days on foot in remote areas of the sweltering Sonoran Desert, located in the Mexican states of Sonora, Baja California, Baja California Sur, and the U.S. states of Arizona and California.

More than 7,000 migrants died during attempted southern border crossings between 2000 and 2020, according to the U.S. Border Control. The actual death toll is likely far higher, because some bodies are never recovered.

UCLA anthropologist Jason De León directs the Undocumented Migration Project, a long-term study of unauthorized migration. In a recent study, De Léon and colleagues modeled the risk of dehydration and death during undocumented border crossings – both now and over the next 30 years. They found that as temperatures warm and desert conditions grow more extreme, more migrants are likely to die from severe dehydration.

Yale Climate Connections spoke with De Léon about the deadly connections between migration and climate change.

This interview has been lightly edited and condensed for clarity.


Yale Climate Connections: What are the main drivers of undocumented migration across the U.S.-Mexico border?

Jason De León: The primary reasons that people attempt undocumented migrations include poverty, political instability, violence of different forms, famine, a devaluation of currency, and, increasingly, climate change.

You’ve got people who are fleeing places like western Mexico because of droughts. They’re fleeing places like Honduras because of the intensity and frequency of hurricanes that are just devastating these places. And so you have all of these migrants who are suddenly having to flee their home countries because of the impacts of global warming. They’re headed towards a country like the United States, which is largely responsible, or one of the key players, in creating this global warming problem. And then they are trying to cross through the Sonoran Desert of Arizona, where they are facing even more risk as these places get hotter because of climate change. And so these folks are being affected by climate change at multiple points in their journey.

The relationship between climate change and migration is for me, one of the most understudied and misunderstood parts of our global migration crisis. I think people have tended to want to separate those two things. And if you look at just Central America in the last couple of years, it is very, very clear that as climate change starts to devastate these very poor countries, people are going to start to be leaving in higher and higher numbers. And so we are now living in a moment with climate refugees. And the United States is going to have to deal with this moving into the future. And this is not a problem that you can solve with the border wall. This is not a problem that you can solve even with guest worker programs. This is a global crisis around climate change that we need to address in many, many different, large-scale ways to better handle this problem.

Listen: Climate change is driving migration to U.S. and making it more dangerous

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When people see a bunch of little kids at the U.S.-Mexico border being dropped off by their parents or by a smuggler or being carried across the Rio Grande or through the desert with their parents, people say, “Oh my God, I can’t believe you would ever do that to your children.” I think the question we should be asking is, how bad must it be in your home country for you to take those kinds of risks with your children? When I look at that, I think, you know, things are horrific. That is the last thing that a parent wants to do is to put their children in danger. But these folks are having to do it because what’s waiting for them back at home in a place like Honduras is famine, hurricanes, political instability, rampant gang violence. So they’re really caught between a rock and a hard place, but they will say to you things like, “I would rather risk my life in the Sonoran Desert of Arizona than watch my children die in San Pedro Sula from starvation or lack of health care or because they were shot on a street corner by some gang.” At least in the Arizona desert, those folks will say that they’re taking some control over their destiny.

YCC: What are the greatest risks migrants face while attempting to enter the U.S.?

Jason De León: In the mid-1990s, the United States developed a border patrol policy called Prevention Through Deterrence. And what that policy tries to do is it fortifies urban ports of entry – so San Diego, El Paso, the town of Nogales in southern Arizona. And it makes it virtually impossible to cross illegally through one of those zones because of the heavy infrastructure. There’s a lot of agents on the ground and motion sensors and helicopters and vehicles.

Because of ramped-up security, people are walking into more and more remote areas where it’s hard for border patrol to get to them, but also, it’s doubling or tripling the amount of time that they’ve spent walking in the desert. And so when I began this project in 2009, most people were walking two to three days in the desert. And now it’s not uncommon to find someone who’s been walking out there for almost two weeks.

Now they have to walk sometimes upwards of 100 miles across vast and treacherous terrain like the Sonoran Desert of Arizona or the South Texas Backwoods. And the idea is that if we force those people to try to cross through those locations, they will be deterred by the physical cost of getting across that terrain. So in a lot of ways, we’ve weaponized the desert as a way to slow down migration, and it’s killed thousands of people. It’s led to the disappearance of thousands of people. And this has been our primary security paradigm along the U.S.-Mexico border since the mid-‘90s.

And we have to keep in mind that for many decades, the primary people coming to the United States from farther south were coming from Mexico. But starting around a little over 10 years ago, we really started to see an increase in folks coming from other countries who had to cross now all of Central America and Mexico in order to get to the United States. And so we’re talking about people from Guatemala, El Salvador, and really right now the majority of folks coming from Honduras as well as farther places like Cuba, Venezuela, Africa. And so those folks now have to cross several countries. They have to deal oftentimes with corrupt immigration agents in various places. They are highly targeted for kidnapping, for assault, for murder. And so now migrants not only have to cross the Sonoran Desert of Arizona, they also have to cross this minefield that has become Mexico.

YCC: You and your colleagues studied water loss for migrants during summer months. Why did you choose that specific risk factor? What did you learn?

Jason De León: You know, I’ve written extensively about the experiences of border crossers: What happens to those who die in the desert? What happens to those who disappear? But much of that has either been sort of forensic or ethnographic – so, talking with the families of the missing and of the deceased, or talking to living migrants about their experiences. And we really wanted to try to find a way to quantify the physiological impact that Prevention Through Deterrence has on the body.

I already could have told you that a lack of water is what’s going to kill you. And it’s impossible to carry enough water. I sort of already knew this anecdotally.  But we did learn, on a more specific level, just how quickly the body becomes dehydrated and we’re able to really quantify the rapid speed at which people lose water.

They’re facing, oftentimes, extreme heat, so they’re losing water at a high rate and they’re not able to replenish that. And we know that the risk of death is very, very high. And so we were interested in really trying to quantify what water loss looks like at the level of the body.

And keep in mind that that in the models that we did, we drew a straight line from point A to point B and said, OK, a migrant would walk from here to there over the course of, you know, three or four days. They would lose a lot of water. They would run out of water by day three or day four. That’s assuming that people are walking on the straightest path with no obstacles in their way. But what we know is that people are taking very circuitous routes to get to a place like Tucson, so they’re winding through the mountains and adding days and days to their journeys. And so, they are on these journeys with a much higher likelihood of death than what our scenarios would even suggest.

YCC: What can be done to save lives?

Jason De León: It’s a great question and always the most difficult one to answer. For me it’s a couple of different things. I think one is we need to understand that we have a border policy in place that weaponizes the Arizona desert and has killed thousands of people, has disappeared thousands of people, and has physically brutalized millions of people.

So for me, one of the first big steps is to cease to use this policy. And if people want to come here and apply for asylum, let them do that. Let them come here legally to go through the legal process.

I think we need to improve our work visa program that allows folks to move back and forth. And work visa programs are very tricky because they oftentimes lead to a lot of exploitation, which is what we had in the ‘50s and ‘60s. It ended up becoming such a problem with abuses against guest workers that we got rid of the program altogether. But I think we need something new that is more sensitive and secure for those who we want to come here and work and be able to move back and forth. I think we need to take a hard look at how much we rely on immigrant labor in this country and recognize and value the value that those folks give to us and treat them better.

But then also, helping these countries to deal with climate change and all the other issues that are happening in their home countries that oftentimes the U.S. has a big hand in. So we think about political stability in Central America: The U.S. has been destabilizing Central America since the early 20th century. We could think about the ways in which we have used exports and the production of U.S. goods in places like Mexico at lower rates that make those jobs really unsustainable for those who are trying to make a living. I think we need to figure out how to have more equal trade agreements, but then also helping those countries to combat climate change as it’s happening in their countries, political corruption, the drug war. In the drug war that’s happening in Mexico, it’s U.S. consumers and European consumers who are the ones who are driving that market. So it’s a lot of different things and people often get frustrated when they ask an anthropologist how to fix these things because it is so complicated. But I think of a big part of it, too, is just understanding that for so long we’ve been convinced that a border wall could solve some kind of a problem or that immigration reform can happen exclusively at the U.S.-Mexico border. And it’s a much bigger problem. It’s a global problem that we need to deal with both domestically and internationally.

Sarah Kennedy

Sarah Kennedy is an editor and content producer with ChavoBart Digital Media (CBDM), a production firm with a focus on scientific and environmental media. Her work on Climate Connections includes developing...