I cannot help but direct readers to an excellent blog by Susan Crockford about polar bear populations, sea ice and the prospects of both. The article is found at
Dr. Crockford provides ten good reasons why one should not worry about polar bear populations. Among the reasons is the fact that there has been no statistically significant rise in temperatures in the last 16 years.
If one does a careful read of the literature, one finds that unregulated hunting was the main reason for declining bear populations and that populations rebounded when governments took steps to regulate hunting. The same was true of the bald eagle: its population was was declining precipitously at one point. The decline was blamed on DDT but the real culprit was unregulated hunting. Once hunting was banned, the bald eagle bounced back.
Much of this is discussed in my recent book:
Climate Change, Climate Science and Economics (Springer, 2013).
Those with access to SpringerLink (most universities) can get an electronic copy much like they can a journal article, or they can purchase a softcover copy via SpringerLink.