In the Arctic, hungry polar bears, unable to sustain themselves on the melting ice, are increasingly making their way inland to such towns as Noorvik, Alaska, and Churchill, Manitoba, where they sniff out garbage bins and scavenge for dinner. And in the Antarctic, wet baby penguin chicks shiver in the rain; warming temperatures mean less snow but more rain, which soaks them through, putting them at risk of freezing to death. These are the consequences of climate change, scientists say.
Polar bears and penguins may live poles apart, with the great white mammals ruling the Arctic areas near the North Pole and the best-known penguin varieties inhabiting the southernmost regions of the globe, in or near Antarctica. But they both depend on ice and cold for survival—a problem in a world that's warming and where temperature increases are most pronounced at the planet's northern and southern extremes. "They don't share the same areas, [but] they share the same problems," says P. Dee Boersma, the Wadsworth endowed chair in conservation science at the University of Washington in Seattle.
Penguins and polar bears are what scientists call "indicator" species; their well-being demonstrates the general health of an ecosystem, says Doug Inkley, a wildlife biologist and senior scientist at the National Wildlife Federation. What they're indicating is "dramatic" changes in both the Arctic and the Antarctic, he says. And these changes could have dire consequences for the penguins and polar bears that inhabit those areas.
Indeed, an increasing number of studies have documented current declines or project future ones for polar bears and for many penguin species. Hal Caswell, senior scientist in the biology department at Woods Hole Oceanographic Institution, has led studies of polar bears in Alaska's Southern Beaufort Sea and emperor penguins (the type featured in the documentary March of the Penguins) in Terre Adélie, Antarctic. Both studies focused on the effects of fluctuations in sea ice and, in particular, on what happens when less sea ice is available. "We found evidence that the population growth was negatively impacted when there were periods of decreasing sea ice," Caswell says. "The populations did not do as well."
Climate change models predict that, as global temperatures rise, periods of reduced sea ice will occur more frequently. Scientists say the amount of ice will still vary because climate change doesn't happen all at once, but the long-term trend points to less and less ice overall. If there are more frequent episodes of reduced ice, polar bear and penguin populations "can't recover in between bad years, so they end up declining over time," says Caswell. That is why the 3,000 breeding pairs of emperor penguins who inhabit Terre Adélie today are projected to decline to 400 breeding pairs by the end of the century.
Sybille Klenzendorf, the World Wildlife Fund's managing director for species conservation, cites studies that spell out similar findings. In Canada's Hudson Bay area, which includes Churchill (nicknamed "the polar bear capital of the world"), there are 25 percent fewer polar bears than 25 years ago. On the Antarctic Peninsula, where air temperatures have warmed about 5 degrees Fahrenheit in the past 50 years, Adélie penguins have declined by 65 percent, and the emperor penguins also are in peril.
Traditionally, polar bears spend most of their time living on or near the ice as they hunt for seals, their preferred food. But over the past 30 years, Arctic sea ice has diminished, with the National Snow and Ice Data Center reporting that 2008 could represent "the lowest volume of Arctic sea ice on record, partly because less multiyear ice is surviving now, and the remaining ice is so thin."
Scarce ice means fewer perches from which polar bears can search for seals (which also have a harder time surviving under these conditions because they, too, are dependent on sea ice). With seal hunting more difficult, bears search for other options. Some swim ever farther out to sea, where they may drown. Others wander inland and turn to scavenging when they come across garbage left by humans. At the same time, with ice forming later each fall and breaking up earlier each spring, female polar bears have less time to feed and store up fat that will allow them to sustain pregnancies and then nurse and care for their cubs long enough for them to survive.