Many regional, national, and global models have examined future water availability. They assume different degrees of global warming, and while the worst-case scenarios offer a generally deteriorating outlook, there are substantial uncertainties depending on necessary assumptions about population growth and therefore water demand. With a warming of up to 2°C, populations exposed to increased, climate change–induced water scarcity may be as low as 500 million and as high as 3.1 billion.[61]
