It's long been shown that the rapidly warming earth is bad news for polar bears. Their habitat is shrinking, as are their food sources and breeding grounds. If global warming continues, they may face a tough competitor. Grizzly bear habitat is limited by frigid winters and sheets of ice. As their world warms up, they're expanding north. The habitats of the two predators are already beginning to overlap. If they continue to do so, the polar bears, not the grizzlies, are going to be the losers in the competition for survival. This is surprising to some. Grizzlies are just a frighteningly-named subspecies of brown bear.