Individual extreme weather events can trigger an exodus of displaced people searching for a new home—in the immediate aftermath of Hurricane Katrina, for example, about a quarter million people were displaced from New Orleans—but many others are driven by environments increasingly hostile to the life they once knew. For example, in South America, Southeast Asia, and North Africa, people relying on farming are abandoning their homes as crop failure increases The influx of people from Central America and Mexico to the US in the coming decades will correlate with the extent of climate warming. A scenario in which modest action is taken to reduce emissions would see about 680,000 migrants coming to the US border; an unabated increase in emissions raises that number to more than one million, and these exclude undocumented immigrants.
Links between mass migration, political instability, and social upheaval have been well-documented. This is one of the reasons that climate change is considered a “threat multiplier” in terms of national security with its potential to tip a society on the brink into conflict. This is an example of another feedback loop in the climate change process: changed environmental conditions spur both conflict and migration; conflict and migration continually reinforce one another.
Migration, like all other climate change consequences, is charged with cruel inequities. On the local level, it is causing residents to shift between neighborhoods within individual cities as, for example, wealthy Miami residents flee the coastline for quickly-developing hilltop neighborhoods like Liberty City, which used to be a predominantly black neighborhood whose long-time residents are finding their lives suddenly unaffordable.