Polar bear hunt from ice flows.Those ice flows are sea ice.Unfortunately, as the earth has warmed, and as the Arctic has warmed even more than the Earth as whole, the summer sea ice pack has shrunk. The polar bears have to swim further and further from one icy formation to another, or from ice to land, because it's harder to find ice, so they're having trouble hunting. they get weak and eventually they succumb. the populations of bears will shrink and they'll become much rarer.