Indeed, a good puzzle for polar-bear science is to answer the question how polar bears survived during the ice ages, when ice covered coastal zones and large parts of the global ocean. Ice was piled miles deep on land, making it extremely difficult for eco-systems to provide enough food. Of course, areas of relative warmth, which population biologists call refugia, always exist. They may well be the key to explaining how polar bears survived the Last Glacial Maximum about 21,000 years ago.
A discussion with Dr. Willie Soon follows here.