Are Polar Bears Endangered?

Yes, polar bears are endangered due to us HUMAN. Due to excessive human hunting for their priceless meat and fur,  the population size of polar bears drastically dwindled from several hundred thousands to a few hundred in a few years time. Another reason that polar bears are endangered by human, is because of that man-made global warming threatens the polar bears' survivals. Polar bears are at risk of extinction because of increased greenhouse gases is causing catastrophic environmental change in Arctic ice area, naming the rapid melting of sea ice. Rapid melting of sea ice eventually cause polar bears to die due to drowning. As ice melted, polar bears are not able to swim that far anymore, and to an extent, the tremendous long distance swimming made them too exhausted to reach solid ice or land. Since polar bears are highly depended on sea ice for survival, they are the first mammal in the world to loose 100 percent of their habitat to global warming(Green, 2008). Other threats are known to be pollution, poaching, and industrial impacts.  According to U.S. Government studies, "two-thirds of the world’s polar bears could disappear by 2050 as global warming continues to melt the arctic’s sea ice" (Roach, 2007).

Here's a link to a video that demonstrates how polar bears act when facing troubling situation:
Video: Polar Bears facing troubling situations.

Melting Sea Ice in Arctic

Not only did the global warming affected the population size and preferred habitat of polar bears, but it also affected the population size of seal in Arctic region. The primary diet of polar bears is the ringed seals, which also reside near ice caps. An easy guess is that when temperature increases, the ice caps melt away, seals migrate to find a colder location, which leaves less food for polar bears to hunt. Less ringed seals exist, less nutrition for polar bears especially female polar bears, which decreases reproduction of polar bear cubs. In feeding on seals, mother seals is trying to store enough fat and nutrition that will last throughout summer and fall. But if she is incapable of storing up enough fat in her body and returns back to her cubs too lean, her milk production will stop and her cubs will die from starvation.(Morrison, 2004)

Here is a link to a video that shows how polar bears hunt for Seal Pups:
Video: Polar Bear hunting Seal Pups.

Table 1 from Kenneth P. Green's article

Since it is impossible to calculate the exact number of polar bears exist, scientist must make population estimates based on limited data. In order to come up with good population estimates, the most prominent way to count polar bears are by capturing and marking a subpopulation of bears, then using the frequency of recapture as a means to estimate the size of population(Green, 2008). The table reported in 2005 above shows that that of the 19 subpopulations of polar bears; 5 were declining, 5 were stable, and 2 were increasing. But, at the 2009 meeting of the IUCN Polar Bear Specialist Group(PBSG), scientists reported that of the 19 subpopulations of polar bears; 8 were declining, 3 were stable, and only one was increasing.(Green, 2008)

Figure 2 from Kenneth P. Green's article

According to the "Sea Ice Index" above, it illustrates that the extent of Arctic sea ice has been declining gradually over time. it also shows how the extent of Arctic ice has varied compared to an average baseline from 1979 to 2000.

Figure 3 from Kenneth P. Green's article

More data on latter trend has been computed by scientists and researchers, as you can see from the figure above, the IPCC's computer modeling projects that the ice in Arctic region will continue to decline in the future up to 2100.

With the combined effects of environmental problems and humans, polar bears are listed as "endangered" species.

References:

Green, Kenneth P. (2008, May). Is the Polar Bear Endangered, or Just Conveniently Charismatic? Retrieved from http://www.aei.org/article/energy-and-the-environment/is-the-polar-bear-endangered-or-just-conveniently-charismatic/

Jon Aars, Nicholas J. Lunn, and Andrew E. Derocher, eds., Polar Bears: Proceedings of the 14th Working Meeting of the IUCN/SSC Polar Bear Specialist Group, 20-24 June 2005, Seattle, Washington, USA (Gland, Switzerland: IUCN, 2006), 33, available at www.polarbearsinternational.org/rsrc/Proc_Seattle05.pdf 

Morrison, J.  (2004, February 1).  The Incredible Shrinking Polar Bears. Retrieved from http://www.nwf.org/News-and-Magazines/National-Wildlife/Animals/Archives/2004/The-Incredible-Shrinking-Polar-Bears.aspx

National Snow and Ice Data Center, "Sea Ice Index," available at http://nsidc.org/data/seaice_index/n_plot.html (accessed April 22, 2008).

Roach, J.  (2007, September).  Most Polar Bears Gone By 2050, Studies Say.  NationalGeographic News. Retrieved from http://news.nationalgeographic.com

United Nations Intergovernmental Panel on Climate Change, Climate Change 2007: The Physical Science Basis (Cambridge: Cambridge University Press, 2007), 339, available at http://ipcc-wg1.ucar.edu/wg1/Report/AR4WG1_Print_Ch04.pdf (accessed April 30, 2008).