Graph

Figure 1: the light blue line show the declining of sea ice extent level from 1979 to 2004.
As the ice level decreases, it has a higher chance endanger to polar bears.
http://www.skepticalscience.com/Arctic-sea-ice-melt-natural-or-man-made.

According to the World Wildlife Funding, the population of the polar bears in May 2002 showed in pie chart. There was 16 of the total population are decreasing, 45 % are stable, around 14% are increasing, and 25% is unknown from the total population.  
http://www.newsofinterest.tv/global_warming/effects/extinction/polar_bears.php

NWF's senior scientist Doug Inkley, Ph.D. explains why polar bears need sea ice and what can happen to them because of global warming.