Polar bears need sea ice to build their dens

     The breeding problem must also be taken into consideration. Since polar bears raise their cubs on Arctic ice, which is breaking up and melting at an alarming rate (“Polar Bears”), their reproduction rates are drastically reduced. Female polar bears usually give birth to two cubs at a time, with the cubs’ survival rate being only 50%. There are two main factors that affect polar bears’ breeding, the sufficient amount of fat to keep themselves warm and nurse cubs, and the thickness of the sea ice to build a den to raise the cubs when they are born (Stirling). With the melting sea ice, mother polar bears cannot store enough energy and nutrition for reproduction, since it has become more difficult to get food. Researchers revealed that from 1985 to 1994, 62% of female polar bears build their dens on the sea ice, but this number declined to only 37% between 1998 and 2004 (Struzik). The consolidated annual Arctic sea ice is going to disappear, so it becomes too unstable to contend with the polar bears’ needs to breed and feed cubs. More and more female polar bears are building their dens on land now, but without the sea ice to hunt prey, these undernourished females are having smaller litters, and giving birth to lighter cubs that do not survive well. Scientists have plenty of evidence to confirm that the polar bear’s fertility rate drops to an abysmal 15% due to the reasons above. They also hint that because the sea ice is decreasing far away from the shore, polar bears can be trapped in the sea one day, and be prevented from reaching their dens (Struzik).