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.