Lack of clean water
Floods and other changes in weather patterns will affect the quality of water, making clean water scarcer than it already is, and devastating droughts will exacerbate the situation. Air pollution from smog, smoke and volcanic ash can further contaminate water, making it unsafe for consumption. Plus, as some areas of the globe become uninhabitable due to desertification, natural disasters, pollution, disease or lack of resources, people will migrate in massive numbers, increasing garbage and water pollution.
And some water might just vanish. Scientists blame global warming for the sudden disappearance of a lake in Chile, climate scientists predict that global warming could dry up many of Africa's rivers, and the Ganges River could be dry in just a matter of years.