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.
If these trends continue, scientists aren't optimistic about polar bears' long-term viability. "Polar bears don't have a very bright future," says Michael Oppenheimer, a professor of geosciences and international affairs at Princeton University. Scientists predict that the polar bear population, currently 20,000 to 25,000, could disappear by the end of the century. If they endure at all, some scientists suggest, it may be by interbreeding with brown bears and eventually evolving back into brown bears—the species scientists believe polar bears evolved from.
Nor is life likely to get easier for penguins, says Boersma, who has studied penguins for nearly 40 years. In the Western Antarctic Peninsula, warming air temperatures (the6-degree rise over the past 50 years is the largest increase in the world) have led to more precipitation in the form of rain, rather than snow, and that spells trouble for Adélie penguins and their chicks. Simply put, increased rain can cause Adélie chicks to die, says Boersma. Newborn and very young chicks do not have the insulating plumage that would keep them dry. When rain falls on their downy outer coats, they become soaked through and are subject to hypothermia. Boersma likens the impact to being wrapped up in a cold, wet sleeping bag in the middle of winter with no chance of drying off. Similarly, emperor penguins are at risk. The emperors depend on stable ice across which the adults and their chicks can march, she says. If the ice breaks up too soon and the chicks fall into the water, they will not survive because their outer coats are not yet waterproof, Boersma says.
Habitats in flux. Adapt or die is the rule by which species live or become extinct, and critics of climate change say that polar bears and penguins will have to adapt, with polar bears moving ever farther north and Antarctic penguins migrating just as far south. But these animal habitats are already in flux, and Klenzendorf says they will also be affected by such additional human-imposed stresses as pollution, the impact of oil and gas development and mining, the disturbance of denning habits and habitats, and the damage done by oil spills.
Moreover, she argues that these already highly adapted animals cannot evolve as rapidly as current climate change models would require. "We can do all the creative work on the ground that we can," she says. "But we will not succeed unless the world gets serious about greenhouse emissions."
Princeton's Oppenheimer, a participant on the Intergovernmental Panel on Climate Change that won the 2007 Nobel Prize, voices similar warnings. "If we get our act together and reduce emissions sufficiently, there is a chance that this does not have to happen," he says. "But it will require prompt action at a substantial level."
Some scientists say that the problems the penguins and the polar bears face at the extremes of the world may serve as a preview of what will happen to the rest of the planet and all other species, including humans. "To me, there are two possible catastrophic circumstances that climate change could lead to," says Edmond Mathez, a curator at the American Museum of Natural History. The first, he says, is rising sea levels that, over the course of the next one or two centuries, could displace "hundreds of millions of people." The second is "rising temperatures [that] will bring on more extensive droughts that will eventually disrupt food supplies." And even though "we don't actually know what the future will bring, we should think of continuing on the same course as being very risky," Mathez says. If the scientists are right, that course could lead to severe consequences for humans as well as penguins and polar bears.