11/15/2012 09:03 am ET | Updated Jan 15, 2013

No Ice, No Ice Bear

When it comes to popular species, polar bears always land near the top. Nobody ever says, "I don't like polar bears." Far from it. When it comes to popular places to see this most popular species, most people land in Churchill, Canada, in the heart of the Western Hudson Bay population. As one of the 19 populations of polar bears in the world, this is the most accessible but also one of the most southern. One rub for these "southern" bears is that they live on the edge of polar bear's range, where they are particularly vulnerable to climate change. One benefit of being accessible is that the bears of Churchill are the best known scientifically of any population. Polar bear research here dates back to the 1970s. This research has allowed for detailed studies on how climate change affects polar bears.

To make a complex story simple, polar bears are threatened by habitat loss. Unfortunately, the dynamic nature of sea ice makes the habitat loss issue tough for some people to grasp. In much of the Arctic, including Hudson Bay, the ice completely melts in summer only to reform in autumn. During the ice-free season, polar bears are forced ashore and lose the sea ice platform that they rely on for hunting, mating, and migration. Polar Bear Photos

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Loss of sea ice in Hudson Bay has been dramatic with the melt occurring up to one month earlier and freeze-up one month later than the 1980s. This might not sound too serious, but polar bears lose access to their prey when their primary habitat melts. Having to bring a hefty amount of body fat with you is what makes the polar bear lifestyle possible. There's no such thing as a "too fat" polar bear. Thanks to ringed seals being incredibly abundant and incredibly fat, polar bears tank up on seal blubber in spring and then use this portable energy store to fast for their on-land "holiday."

The problem for the bears in Hudson Bay is that the holiday is getting too long. While an extended holiday for us might sound appealing, we know that draining down the bank account could result in dire consequences. For polar bears, an increasing holiday is turning into a disaster. Pregnant females in Hudson Bay have to bring enough energy ashore to last eight months without eating. These bears are already at the limit and pushing them to nine or 10 months without food means they can't produce the next generations. We're getting to this point and recruitment of new polar bears is dwindling. If females do manage to give birth, they are again at risk when they have to spend the summer onshore. When mother bears run out of their banked energy (fat stores), they stop nursing their cubs. Ending lactation happens in all mammals when energy stores are depleted. The trouble comes for growing cubs that don't have a large fat store of their own. Once Mom stops providing milk, they quickly deplete their energy stores. If mothers and cubs are delayed in getting back on the sea ice to resume feeding, the cubs can die of starvation. Research shows that climate change affects the young and old most severely. One has to wonder if there won't be a parallel with human populations.

With a north-to-south distribution similar to the distance between New York and Los Angeles, there's a lot of variation in what each of the 19 polar bear populations is seeing and will see as climate change continues. We'll likely lose the polar bears in Hudson Bay before too long -- by mid-century, but more likely in the next decade or two. Nonetheless, the bears are doing okay in some other areas and will do so for some time to come. Winters will still get cold in the high Arctic even with climate change. We may hold onto polar bears as a species to the end of the century, but this is predicated on many hopeful elements. As one of the first species to be listed as threatened by climate change, polar bears are an indicator.

Are polar bears the canary in the coal mine? Well, they're only slightly yellow, don't fit in tiny cages, and they aren't birds, but in some ways they're related to coal mines. It's the end product of coal mining and burning of other fossil fuels that are causing the problems for the ice bear. No ice -- no ice bear. It isn't complicated, but the solutions will be and polar bears are running out of time for us to find them.