The Western Antarctic Peninsula is one of the most rapidly warming areas on the earth: In just the past half-century, its temperatures have risen by 10.8 degrees Fahrenheit. Adélie penguins rely on the ice to live and global warming is taking its toll on their numbers, though not exactly in ways one might think.
Indeed, Adélie penguin colonies on the Antarctic Peninsula, on the northern edge of Antarctica, have declined by 90 percent, and the only colony of emperor penguins that once lived there is now extinct. But it turns out that elsewhere, specifically in the Ross Sea, a southern extension of the Pacific Ocean, Adélie colonies have been growing significantly, as winter sea ice cover grows there.
Indeed, climate change has benefited penguins in some ways, as the New York Times observes:
...in the Ross Sea a reverse trend is occurring: Winter sea ice cover is growing, and Adélie populations are actually thriving. The Cape Royds colony grew more than 10 percent every year, until 2001, when an iceberg roughly the size of Jamaica calved off the Ross Sea ice shelf and forced residents to move 70 kilometers north to find open water. (The iceberg broke up in 2006, and the colony of 1,400 breeding pairs is now recovering robustly.) Across Ross Island, the Adélie colony at Cape Crozier -- one of the largest known, with an estimated 230,000 breeding pairs -- has increased by about 20 percent.
Climate change has created a paradise for some pack ice penguin colonies and a purgatory for others, but the long-term fate of all Adélie and emperor penguins seems sealed, as relentless warming eventually pulls their rug of sea ice out from under them. Some scientists attribute the recent sea ice growth in the Ross Sea to the persistent ozone hole, a legacy of the human use of chlorofluorocarbons that cools the upper atmosphere over the continent, increasing the temperature difference with the lower atmosphere and equator, and over the last 30 years has delivered significantly brisker westerly winds in the summer and autumn. The warming of Earth's middle latitudes is having a similar effect, increasing that temperature difference and sending stronger winds that push sea ice off the coast and expose pockets of open water, called polynyas, that give nesting Adélie penguins easier access to food.
Despite this, the fate of the penguins seems sealed. As the boundary of the sea ice retreats south, the penguins' chances for survival diminishes. Global warming has also had a drastic effect on the food chain: A recent study in the Proceedings of the National Academy of Sciences has found that the warmer temperatures are killing off as much as 80 percent of the phytoplankton that grow under ice floes and the krill, a staple of the penguin diet.
Further, temperatures are rising in the Ross Sea: The average summer temperature at McMurdo Station, the American research base on Ross Island, has gone up 2.7 degrees Fahrenheit in the past 30 years, which is more than the global average. As the ice pack melts, the Ross Sea penguins will have no choice but to "shift their range farther south toward the pole."
David Ainley, an ecologist with the consulting firm H. T. Harvey and Associates who has been studying Ross Sea penguins for 40 years, notes that the penguins "appear to need light -- if only twilight -- to forage and navigate, and as comfort against predators." As the Adélie penguins have to go further south as the pack ice retreats, they may face extinction not only because their habitat is gone, but because of an "unshakable fear of darkness" -- because they find themselves living in a dark part of the world far from where they once made their colonies.
This video shows Adélie penguins on Ross Island, their home for the time being.