“Polar bears survive by hunting seals,” explains environmental scientist, Dana Nuccitelli : “To reach their prey, they need a platform of ice floating on the sea where seals live.” Unfortunately, ice platforms have melted in several regions where the bears hunt as global warming has heated up the Arctic faster than the rest of our earth.
Nuccitelli notes: “However, one myth argues that polar bear numbers are greater now than in the 1970s so they’re in no danger from global warming. … [P]olar bear populations may have been in even worse shape than they are today. But this claim is an oversimplification.”
In the mid-20th Century, hunters killed over 1,000 bears each year, prompting enactment of hunting regulations, allowing dwindling bear populations to recover. However, just because bear populations recovered from the hunting threat does not mean we can jump to the conclusion that they are not now being compromised by global warming which, in some regions, is destroying sea ice platforms they use to hunt seals. 
Sea ice melt is not the same in every Artic region. Around Canada’s Hudson Bay, sea ice is seasonal melting earlier every summer, re-freezing later every fall, creating longer ice-free seasons, as if God were indifferent to the difficulties human-caused warming has foisted on seal-deprived polar bears, bears that now devoir eggs, chicks, or ground-nesting adult shore birds like snow geese. [2a] [2b] When they can catch them, bears also have eaten dolphins. However, swimming bears have also been eaten by killer whales that have migrated into their warmer waters.
As sea ice melts earlier, Polar bears are moving to land earlier. They eat very little while on land. So they do not have time to build up sufficient fat reserves to survive the lengthened ice-free season. For every week a bear has not been hunting, it becomes 22 pounds lighter. Also, if a female bear’s weight falls too much, it will not conceive. Between 1981 and 1998, Hudson Bay scientists observed that the bear weight and number of cubs born declined by 15 percent. In Western Hudson Bay where the sea ice is seasonal, the polar bear numbers have declined by 22% over the past 30 years.
In other “divergent ice regions,” like the southern Beaufort Sea, Nuccitelli notes, “sea ice retreats from the shore during the summer, like a retracting bridge.” There the polar bear population shrunk from 1,600 bears in 2004 to 900 in 2010. 
In the summer of 1975 pack ice was seven miles offshore from Cooper Island near Barrow, Alaska. By 2008 it was 250 miles away, causing migration away from shore of Arctic Cod the main food source for the Guilllemot, a sea bird, which like the polar bear, must forage farther to feed its young because the sea ice is melting. 
When ice retreats, if bears do not come ashore, foregoing seal hunting until the ice returns, they must swim long distances to reach the remaining ice to hunt. Cub-loss during such swims is not an isolated event. 
So it is clear: while bear populations seem stable or increasing for now in a few northern artic areas,  human-caused global warming is endangering polar bears and compromising Black Guillemots where sea ice they need to hunt is melting.
And for Planet Earth for Kids link to “Global Warming: Melting kingdom of the Polar Bear,” click here