This summer, a drought in Central America’s Dry Corridor—a swath of historically arid land that runs through Honduras, Guatemala, Nicaragua, and El Salvador—decimated 80 percent of the region’s maize and bean crops. By August, Honduras declared a state of emergency.

By September, what would have been a time to harvest and store crops became yet another exodus, following a long line of migrants who have left Honduras in recent years. Individuals and families made plans, first via Facebook and then via the news and word of mouth, to travel together toward the United States.

On October 12, a group of a few hundred people set forth from San Pedro Sula, Honduras—one of the most dangerous cities in one of the most dangerous countries on Earth—and began walking to Guatemala. Moving en masse provided protection from criminals and officials who prey and profit off migrants, as well as political visibility in the face of an increasingly xenophobic U.S. government. By the time the migrants crossed the border into Mexico a little over three weeks later, the caravan had swollen to several thousand people. They traveled on foot, parents pushed strollers and carried their babies on their backs. Men, women, solo teenagers, and small children walked for miles and miles, their feet swelling and pocked with blisters.

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According to migration experts, and to the hundreds upon hundreds of migrants whom I have interviewed while researching a book on migration from Central America, migrants are leaving Honduras, El Salvador, and Guatemala—a region known as the Northern Triangle—because of a complex set of factors: poverty, the need to reunite with family, and violence, largely at the hands of the region’s brutal gangs. But what we don’t hear as much about is the compounding impact that climate change has on migration from Central America to the United States.

In Honduras, 65 percent of people live in poverty, and 14 percent of the economy is reliant upon agriculture. And yet agriculture in Honduras is a risky livelihood—this is the second major drought the country has experienced in two years. The average temperature in Honduras has already increased over 1 degree Fahrenheit in the last decade. Rainfall in Honduras is set to drop by about 10 percent by the year 2050. Sea levels will rise, and the droughts, floods, landslides, and tropical storms that have devastated residents of the Northern Triangle will increase too.

In El Salvador, agriculture is even more critical—21 percent of its people work in an imperiled agriculture sector, and the country’s rivers are drying up. In Guatemala, the semiarid region is seeping outward to encompass more territory, and the United Nations predicts more floods and droughts in years to come.

Climate change is not only impacting subsistence farming and food supplies, but also one of the Northern Triangle’s key cash crops: coffee. Coffee is one of the few reliably profitable exports in Central America, and harvests declined dramatically during the recent drought. According to Coffee & Climate, a climate adaptation project funded by the coffee industry, worldwide coffee production is projected to drop by at least 40 percent by the year 2050.

Environmental degradation has been a compounding factor of both migration and violence since time immemorial. When there was no food in the regions they were hunting and gathering, early humans merely moved on. And as our world became more populated and we began to more commonly live alongside neighbors in permanent communities, all was well when there were enough resources to go around. Once water, land, or food began to grow scarce, violence began.

We see this in recent conflicts too. Genocidal campaigns against black Sudanese in Darfur were rooted in deep racism, but the turning point was water scarcity and low-level conflict over access to wells. The Rwandan genocide was instigated by politicians looking to consolidate power, but these politicians drummed up the majority Hutu—a largely agricultural group—against the Tutsi—who were historically animal farmers—by exploiting limited resources. Today’s conflicts in Syria and Yemen can be traced back, in part, to fights over water.

Unfortunately, this resource scarcity and conflict overwhelmingly impacts people in the global south, where the impacts of climate change are the worst. When the world heats up, people become hungry and thirsty. And hungry and thirsty people will both fight and move to save their own lives.

Our current international framework for forced migration—which is routed in the 1951 refugee convention—provides no framework for economic migrants. Migrating because of poverty—even dire and life threatening poverty—does not a refugee make. The same goes for climate migrants. Though the United Nations has estimated that more than 22 million people have been displaced by climate change or extreme weather events since 2008, there is still no international protective framework for those fleeing because of climate change, or the millions more who will do so in the decades to come.

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Years ago, when I was reporting on environmental migration in East Africa, I spoke to a group of men from southern Ethiopia, all farmers, who were holed up together in a Nairobi slum. They slept among large, blue barrels fizzing with fermenting injera dough, which they brewed in exchange for a place to lay their heads at night while they figured out their next move. They’d left their wives and children and brothers and sisters and parents at home in Ethiopia. Why? Because, they told me, it had become too difficult to farm back home; the rains weren’t enough when it was time to plant. When it was time to harvest, the rains came suddenly and swiftly, ruining the crop.

The Ethiopian men didn’t name climate change as the reason that they had left; in fact, they’d never heard of it. When I offered a rudimentary explanation through my translator—the notion that too much air pollution has changed our weather patterns and global temperature—they shook their heads.

“No,” the eldest said. It couldn’t have been climate change that caused the problems back home, he explained, because the air where they lived in Ethiopia was clean and pristine. There weren’t a lot of cars or factories there. Maybe climate change was happening elsewhere, he said, but not in Ethiopia.

In fact, like El Salvador, Honduras, and Guatemala, Ethiopia is one of the places where climate change has hit hardest, even though, as the Ethiopian farmer intuited, they are one of the lowest contributors to global carbon emissions. A cruel irony of climate-related migration is that the people forced out of their homes are most often living in areas that contribute the least to the problem.

My conversation with the Ethiopian farmers was back in 2011, when fewer people had heard of climate change. But I thought of that moment years later, when I was working on my book about twin brothers who were forced out of El Salvador at the age of 17. I asked their father, Wilber, a farmer in his sixties with a second-grade education and a green thumb—who offered me miraculous advice about my wilting backyard garden thousands of miles away—why it was that he thought his tomatoes weren’t growing well this year. Why wasn’t his land—beautiful, fertile land that had fed his family for years—having the same yields?

He had a sense that it was some international issue, but his theories and evidence were vague; some dust, he had heard, may have come from Africa and settled onto his crops. Who knew if it was true, he said, but what he was sure of was that something was happening in the world that was impacting his crops. The causes were somewhat irrelevant, anyway. What mattered was his ability to feed his family. Three of his children had already left El Salvador for the United States. If he couldn’t make things work in the fields, more of them would have to consider moving north.

Another migrant caravan left from El Salvador on October 28, and a few days later, yet another. On November 18, according to reports from El Salvador, a fourth migrant caravan is scheduled to depart.

Meanwhile, the migrants in the caravan walk through rivers, sleep in town squares, cover their blisters, wait in line for food, and make their way toward the U.S. border where thousands of troops are patrolling miles of fence, wall, and razor wire. Many politicians and news outlets continue to cast them as a greedy, illegal horde of invaders, trying to take advantage of U.S. policies and economies. Yet the journey they are taking is a grueling one and full of risks, and a trip that is not taken without cause.

Climate change may not be the reason people name when asked why they leave their homes behind and head out into the unknown, but it is an immensely complicating factor, and sometimes a final straw. People don’t always know what has caused their homes to become unlivable—what historical, political, and economic nuances have made it possible for the gangs to grow like weeds and for the dead to pile up in the morgues and for the fields to dry up—but when the stakes are this high, they rarely stick around to find out.

Funding for a portion of the reporting of this article was provided by the Pulitzer Center for Crisis Reporting.