Estimates for how many people will relocate because of climate change vary between 25 million to 1 billion by mid century, according to the UN International Organization for Migration (IOM). The UN warns that by 2045, 135 million people may be displaced by desertification alone.
Last year, the IMO suggested that governments respond with policies such as "ensuring migration pathways via free movement protocols" and "expediting or waiving visas."
But in his book 'Storming the Wall: Climate Change, Migration, and Homeland Security,' Todd Miller argues that some countries are instead putting up barricades to keep them out.
"You see this emphasis on border enforcement, on creating these hardened lines of division," Miller told DW, "and so often, they are going up against countries that have a lot of issues to do with ecological events and climate change."
Caravans flee Central America's Dry Corridor
Donald Trump may profess not to believe in climate change, but it could be a factor driving support for his signature border wall. Miller argues that a zone of drought known as the "Dry Corridor," where crops are failing and livestock is perishing, has exacerbated tensions on the US-Mexican border.
"One of the things about the Dry Corridor is that 15 years ago that term didn't even exist," Miller says. "So this is kind of a new term — you can almost say it's a manifestation of the changing climate."
Last year, Guatemala, El Salvador and Honduras reported combined losses of 281,000 hectares (694,000 acres) of staple crops due to drought. It was in these three countries that migrant caravans formed and headed north, making for striking media reports and fueling US anxieties over immigration.
In Europe, fears over migration exploded in 2015 and 2016, when an estimated million people arrived, mainly from Africa and the Middle East.
One European Union response was to turn its border agency, Frontex, into a full European Border and Coast Guard, giving it control over its own budget, which was raised to €238 million ($268 million) — nearly 38 times what it was a decade earlier — as well as the authority to compel member states to secure their borders.
"Especially since 2015 — the start of the so-called refugee crisis — it's really been a militarization of European borders and beyond," Mark Akkerman of Dutch organization Stop Wapenhandel, who has authored a series of reports on how military and security companies have profited from the crisis, told DW.
Miller says the militarization of borders is a global trend: When the Berlin Wall fell in 1989, there were just 15 border walls across the globe. Today there are 77.
Meteorological margins push against political borders
Some people are driven to leave their homes directly because of drought or flood. But the role of climate change in migration is often far more complex. In January, the UN Security Council held a debate framing global warming as a "threat multiplier."
Crop failures, natural disasters and depleted resources — be they fertile soils or water — can tip delicate economic and political balances into crisis, fueling poverty and conflict.
In their book 'Conflict Shoreline,' Eyal Weizman and Fazal Sheikh of interdisciplinary research group Forensic Architecture, examine the world's longest aridity line — where the minimum amount of rain falls to support cereal crops without artificial irrigation. Livelihoods in these conditions are highly sensitive to changes in climate.
The line runs through sites of recent conflict including southern Gaza, Helmand, and Daraa, where the Syrian uprising first broke out in 2011 following unprecedented drought. The team also plotted Western drone strikes onto meteorological maps and found that "many of these attacks — from South Waziristan through northern Yemen, Somalia, Mali, Iraq, Gaza, and Libya — were directly on or close to" the aridity line.
Researchers at Columbia University, meanwhile, have shown that between 2000 and 2014, temperatures deviating from the norm in countries migrants come from correlated with increased asylum applications in Europe.
Climate change, migration and terror
The EU did not make Frontex what it is today as a direct response to climate change. But Akkerman says it's hard to imagine decisions over European border policy are completely unaffected by the knowledge that immigration is likely to increase — due to a variety of factors.
"Climate change is one of those factors," he says. "I think the EU definitely does take that into account even if they don't say it out loud at the moment."
In the US though, the link between global warming and border security has been explicit. In 2010, Washington officially listed climate change as a threat to national security. That, Miller explains, required the Department of Homeland Security — which deals with border and immigration enforcement — to formulate a response.
"You see this top-level consciousness of what climate change could bring," Miller says. "And things like the droughts in Central America are mentioned in those papers." The result was "the US government saying, we have to build up our borders due to mass migration."
In Europe, too, Akkerman points to politicians increasingly framing climate change and migration, which often gets linked to terrorism, as a security threats rather than humanitarian crises.
"And if you frame something as a security threat, step two is looking for military means to combat that," he says.
Since 2014, the EU has replaced Mediterranean search-and-rescue missions with operations whose primary focus is security and border enforcement.
Across Europe, politicians — from Italian nationalists to the Conservative British government that cancelled its funding for search-and-rescue in 2013 — and Frontex itself, have argued that rescues act as a "pull factor" encouraging migrants to make the journey.
But experts say there is no evidence for this. Moreover, tightening borders just forces people to take riskier journeys. "This trend is continuing, things are becoming more and more dangerous because more and more routes are closed," says Ramona Lenz, a cultural anthropologist with aid organization Medico International.
According to the Heinrich Boll Foundation, the death rate among those trying to cross the Mediterranean has increased nine times since 2015.
"There is much more violence towards refugees and migrants and it is much more accepted," Lenz says.
Nationalism in a globalized world
In the wake of the 2015-2016 migrant influx, far-right politics has entered the mainstream around Europe. But Lenz says solutions demand the very opposite of nationalism: inclusive thinking that understands the interconnected flows of resources, waste, emissions, money and people across the globe.
"If we go on like this, migration will increase, more people will have to leave their homes and look for other places to stay," she says. "We know that and we don't want to be confronted with this complexity — the complexity of a globalized world — so we look for simple solutions. But they won't work out for long."
Ultimately, the climatic changes that are making parts of the world unlivable are another example of people in poorer parts of the world paying the price of Western lifestyles.
"If we really want to change something we have to start in industrialized countries," Lenz says, "with how we consume, how we buy things, how we live — we would have to change very basic things that concern our own lives."