A new study has found that a lack of sea ice in northern regions is not only making it more difficult for bears to find food, but is also causing their litter sizes to be reduced.

Peter Molnar of the University of Alberta published his findings in a recent issue of Nature Communications. Molnar examined a population of nearly 1,200 polar bears in the west Hudson Bay region of Canada, close to the town of Churchill, Manitoba, where the bears migrate every year.

Using comparative data from the early 1990s, Molnar found that females were often giving birth to triplets and twins. Now, most pregnancies only produce a single cub, and the rate of miscarriage has gone up as well.

According to Molnar, the reason stems from a lack of body fat and energy storage by the females. Pregnant bears must find extra food in order to support the cubs, but this is difficult because of the lack of sea ice. Bears use the sea ice to hunt for seals, but higher temperatures caused by global warming means that the ice is breaking up sooner and sooner. The study theorizes that if the ice breaks up just one month earlier, between 40 and 70 percent of the population will not be able to reproduce.

"When little food is available," the study states, "polar bears are known to rely on stores of energy for survival and reproduction. The reliance on energy stores in pregnant females however, limits the survival rates of their cubs."