War, poverty, and oppression have forced hundreds of thousands to flee their home countries in the Middle East and sub-Saharan Africa, pushing affected populations to abandon their livelihoods and seek asylum in Europe. But another threat looms not far behind, and though it might seem less menacing, it is exactly the kind of disaster that could wreak havoc on the region, driving displacement at an unprecedented rate. That threat is climate change.

"You think migration is a challenge in Europe today because of extremism, 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," U.S. Secretary of State John Kerry recently warned at a climate conference in Alaska.

As the world continues to warm, rising temperatures and extreme weather will inevitably lead millions around the world to leave their home in search for water and other agricultural resources, according to António Guterres, the United Nations High Commissioner for Refugees. "Not only states, but cultures and identities will be drowned," he said in 2009.

This has been a year of record-shattering temperatures, with several countries in the Middle East experiencing a dangerous "heat dome." Bandar Mahshahr, Iran, registered a staggering 164 degrees Fahrenheit on the heat index this summer, and the Iraqi government imposed a four-day mandatory holiday in response to the heat wave.

The relationship between migration and climate change has already been established, to an extent. Between 2008 and 2014, approximately 38 million people were displaced by environmental disasters each year, the Internal Displacement Monitoring Center reported. That's nearly three times as many people as were displaced by conflict and violence.

Dr. Richard Seager, a professor at Columbia University, published a report in March that discussed the influence of climate change on the Syrian conflict. Syria is currently experiencing a civil war, and many refugees seeking asylum in Europe come from the country.

"Syria was destabilized by 1.5 million migrants from rural communities fleeing a three-year drought that was made more intense and persistent by human-driven climate change, which is steadily making the whole eastern Mediterranean and Middle East region even more arid," Seager told the Independent.

"Syria is not the only country affected by this drying," he added. "Lebanon, Jordan, Israel, Iraq and Iran are too. However, the various social, religious and ethnic wars play out, in the coming years and decades the region will feel the stress of declining water resources."

As many as 200 million people could be overtaken by global warming, Norman Myers, an environmentalist at Oxford University, wrote in 2005.

"All in all, the issue of environmental refugees promises to rank as one of the foremost human crises of our times," Myers wrote. "To date, however, it has been viewed as a peripheral concern, a kind of aberration from the normal order of things--even though it is an outward manifestation of profound deprivation and despair."

"While it derives primarily from environmental problems, it generates myriad problems of political, social and economic sorts. As such, it could readily become a cause of turmoil and confrontation, leading to conflict and violence. Yet as the problem becomes more pressing, our policy responses fall ever-further short of measuring up to the challenge. To repeat a pivotal point: environmental refugees have still to be officially recognized as a problem at all."

Related: 8 Powerful Statements From Pope Francis On Climate Change