CREDIT: REBECCA BLACKWELL/ASSOCIATED PRESS. 2-year-old Aliou Seyni Diallo eats dry couscous given to him by a neighbor, after he collapsed in tears of hunger in the village of Goudoude Diobe, in the Matam region of northeastern Senegal, Tuesday, May 1, 2012.

The hundreds of thousands of migrants arriving in Europe or dying on the way to its shores could be a harbinger of things to come, researchers and policymakers warn, because a potentially greater driver of displacement looms on the horizon: climate change.

As U.S. Secretary of State John Kerry warned at a recent State Department-led conference on climate change in the Arctic, the scenes of chaos and heartbreak in Europe will be repeated globally unless the world acts to mitigate climate change.

“Wait until you see what happens when there’s an absence of water, an absence of food, or one tribe fighting against another for mere survival,” Kerry said.

World leaders have long warned that natural disasters and degraded environments linked to climate change could — indeed, have already started to — drive people from their homes. UN High Commissioner for Refugees António Guterres declared in 2009 that climate change will create millions of refugees and internally displaced populations. “Not only states, but cultures and identities will be drowned,” Guterres said.

Displacement is already happening in some parts of the world. Almost 28 million people on average were displaced by environmental disasters every year between 2008 and 2013, according to the Internal Displacement Monitoring Center — roughly three times as many as were forced from their homes by conflict and violence.

It’s difficult to predict exactly how many more may be displaced as climate change progresses. “When global warming takes hold there could be as many as 200 million people overtaken” by the consequences, professor Norman Myers of Oxford University argued in a 2005 paper. For comparison’s sake, 350,000 migrants sought entry into the  European Union in 2014, the International Organization for Migration estimated.

Few countries or international organizations are prepared to deal with environmentally displaced people. As a 2011 report from the European Parliament’s Directorate-General for Internal Policies detailed, there is no specific legal protection for “environmentally displaced individuals” beyond temporary measures that would prove insufficient if the environmental damage to their homeland endured.

The UN has a non-binding agreement on internal displacement from 1998 that includes provisions for people fleeing natural disasters, but it is not obligatory and includes no penalties for countries that ignore it, as Roger Zetter, a professor emeritus in refugee studies at Oxford, told The Huffington Post. The portions addressing natural disasters focus on storms, not the more complex and slow-onset effects of climate change.

Myers’ sensational prediction of hundreds of millions of climate change refugees has come under fire in the years since its 2005 publication. “It’s a very contentious overestimate,” Zetter said. “It’s a back-of-the-envelope figure.”

It’s difficult, if not impossible, to get data on the number of current migrants who left their homes primarily because of climate change. For most, environmental degradation is one factor among many, Zetter and other experts cautioned. Nevertheless, climate change-related environmental impacts will present “very significant challenges,” Zetter said.

“What climate change and displacement do is present developmental problems for countries that are already struggling,” he explained. “If you’ve got to start spending more and more money on flood relief channels or earthquake-proof buildings or increasing huge water transfer programs to cope with depleting aquifers, there’s no question that it will add a huge additional financial burden and make planning and development strategies more difficult.” 

And for some countries, climate change poses an immediate and very real threat — countries like the small island states threatened by rising seas. “If there’s no land, they’ll have to leave,” Zetter said.

CREDIT: RICHARD VOGEL/ASSOCIATED PRESS. In this March 30, 2004 file photo, a man fishes on a bridge on Tarawa atoll, Kiribati. Fearing that climate change could wipe out their entire Pacific archipelago, the leaders of Kiribati are considering an unusual backup plan: moving the populace to Fiji.

That includes places like Kiribati, a country made up of 33 islands in the remote South Pacific. Kiribati will be among the first countries to vanish beneath the rising ocean, possibly as soon as the end of this century. But long before then, its atolls and reef islands will be uninhabitable for their 103,000 residents if a violent storm comes crashing through, or if the ocean seeps into their already inadequate supply of fresh groundwater. Half of the country’s citizens live on the Tarawa Atoll, a crescent of white sand two-thirds of a mile across whose highest point is just 10 feet above the ocean.

Operating on the unfortunate assumption that the sea will swallow the country, the government of Kiribati purchased 6,000 acres of land in Fiji last year, in case they need to uproot an entire people and put them somewhere else.

Major storms and flooding already cause tremendous displacement — almost 28 million per year on average, according to the Internal Displacement Monitoring Center. Many more are affected, but not necessarily displaced — an average of 140 million people yearly, the International Panel on Climate Change reports. Scientists expect climate change to make violent storms like Typhoon Haiyan, which forced a million people to flee their homes in the Philippines in 2013, stronger and more frequent.

Typhoons and monsoon floods hit people hard and fast, forcing them to literally flee for their lives. Scientists call those rapid-onset climate events. But there are also slow-onset climate events like drought, desertification and sea level rise.

These slow-moving changes are “much more difficult to relate to mobility patterns,” Albert Kraler, a program manager for research at the International Center for Migration Policy Development in Vienna, told HuffPost. Often, environmental changes are just “one of the factors informing people’s migration choices.”

Despite the difficulty in determining exact numbers, the United Nations Environment Program concluded in a 2011 study on the Sahel, a semi-arid belt across northern Africa, that “migration occurs when livelihoods cannot be maintained, especially when agriculture or herding is severely affected by environmental degradation or extreme events.”

The changes in the Sahel are perhaps the most obvious example of slow-onset events. The UN dubbed the region “ground zero” for climate change “due to its extreme climatic conditions and highly vulnerable population.” Its arid climate and infrequent rain are getting worse, and scientists blame climate change. The rain is less predictable than it used to be — sometimes there is too much and sometimes nowhere near enough. For almost everyone in the Sahel, food has become more expensive and scarcer. As a result, 30 percent of households in Burkina Faso, in the heart of the Sahel, have relocated in the last 20 years because they could no longer survive, The Guardian reported in 2013.

People have always migrated across this region. But these days, “the traditional temporary and seasonal migration patterns of many farmers, herders and fishermen in the region are increasingly being replaced by a more permanent shift southward and to urban areas,” UNEP reports. “Nearly half of the West African population now lives in largely overcrowded coastal cities, including 12 townships of over one million inhabitants along the coastline from Senegal to Nigeria.”

The population of the Sahel region is expected to skyrocket over the next few decades. Competition between tribes and ethnic groups, pastoralists, farmers and fishermen over ever-scarcer natural resources, which has existed for as long as people have lived there, is becoming intense. And then there’s Boko Haram. Its fighters have set up camps on islands emerging out of Lake Chad, a once-majestic expanse of fresh water that in the past supported millions of people in the heart of the Sahel. But the lake has lost 90 percent of its area since the 1960s. Now, there’s a militant Muslim fundamentalist insurgency taking hold amid an ongoing environmental disaster.

CREDIT: BEN CURTIS/ASSOCIATED PRESS. A dead donkey lies partially covered by the wind-swept sand near the village of Dala in the Sahel belt of Chad, Friday, April 20, 2012. UNICEF estimates that 127,000 children under five in Chad’s Sahel belt will require lifesaving treatment for severe acute malnutrition this year, with an estimated 1 million expected throughout the wider Sahel region. The organization says the current food and nutrition crisis stems from scarce rainfalls in 2011, which caused poor harvests and livestock production.

Climate change is also a factor in the worsening storms and environmental degradation of coastal South Asia — factors that, when combined with mismanagement and political dysfunction, are putting millions of people at risk. Some have already started to migrate because their ways of living are becoming impossible. In the Indus delta in Pakistan, entire villages have been wiped off the map. Bangladeshis and Indians in the Sundarbans, a vast mangrove forest where the Ganges meets the sea, are heading inland, away from the rising ocean and the increasingly saline farmland.

Bangladesh is expected to be the largest single source of climate refugees, with up to 30 million people at risk. Many end up in slums in cities like Dhaka, Bangladesh’s capital and the world’s fastest-growing megacity. Some 70 percent of Dhaka’s slum dwellers moved there because of environmental degradation, according to the International Organization for Migration.

Migrants and refugees across the world, driven by rapid-onset natural disasters or by a complex combination of the more slow-moving effects of a changing climate, are already putting immense strain on the countries and cities they end up in. A lot of the time locals aren’t happy to see them, and many governments have been caught unprepared and unwilling to take them in.

Already, migrants and refugees across the world are already putting immense strain on the countries and cities where they end up.

In Europe, Hungary is putting up a fence to keep migrants and refugees out. “We don’t want to [live together with Muslims],” Hungary’s prime minister Victor Orban said on Thursday, “and I think we have a right to decide that we do not want a large number of Muslim people in our country.”

CREDIT: MARK BAKER/ASSOCIATED PRESS. Detainees sit in a detention center on the outskirts of Kuala Lumpur, Malaysia, July 23, 2009. Australia came under fire from the U.N. children’s aid agency and human rights advocates June 3, 2011, over its plan to send unaccompanied child asylum seekers to Malaysia under a refugee swap deal.

For the past two years, Australia has deployed its navy to force migrants and asylum-seekers away. The government allegedly bribed one captain more than $30,000 to take his boatload of migrants to Indonesia. Other migrants are being held in detention centers on tiny islands like Nauru, where, according to an Australian Senate committee report, children are sexually abused and guards offer weed in exchange for sex.

As for America, when residents of Kivalina, a Native village in northwestern Alaska that is rapidly disappearing into the ocean, tried to get the government to lend a hand, the response they received was that “there’s no agency set up to address those questions.”

Europe’s handling of the current refugee situation doesn’t bode well for a future in which vulnerable populations fleeing the effects of climate change are again knocking at their doors. Nor does it seem likely that Western countries will embark on the expensive and challenging task of helping at-risk countries prepare, as John Kerry warned we must do. The Western world is facing a lot of tough questions, Zetter said.

“We’ve not faced up to the challenge that we obviously are the emitters, that we are creating climate change, that we are creating this additional pressure on the developmental trajectories that many countries face,” he said.