THE STUDY “A 45,000-Year-Record of Adélie Penguins and Climate Change in the Ross Sea, Antarctica” by Steven Emslie, Larry Coats, and Kathy Licht in the January 2007 issue of Geology. 
THE MOTIVE For millions of years, Antarctica’s ice sheet has advanced and retreated as Earth has cooled and warmed. Covering nearly 5.5 million square miles, the frozen mass exerts an enormous influence on the global climate, reflecting sunlight back into space and cooling Earth’s atmosphere and oceans. If the ice sheet were to melt, global temperatures would rise 8 to 10 degrees Celsius. Yet dating past expansions and contractions of the Antarctic ice shelf has proved difficult. Geologists can infer its changing size by dating marine sediments, but this method is not always accurate. Now Steve Emslie, a marine ornithologist at the University of North Carolina Wilmington, has developed an ingenious method of tracking climate change in the Antarctic: He has excavated and carbon-dated 45,000 years’ worth of Adélie penguin poop, skin, bones, feathers, and eggshells from colonies preserved in Antarctica’s frigid climate. Because these birds nest only on ice-free terrain, the presence of their ancient nesting sites indicates when the glacial ice sheet had retreated; their absence indicates the ice had returned.
THE MEANING “Penguin colonies have been blinking in and out of the Ross Sea over time with climate change,” says Emslie, and this research puts “a better absolute date on when there was open water, which is the first time we’ve been able to do that.” Prior to this work, geologists did not know exactly when the Ross ice shelf began to advance. Thanks to Emslie’s penguin findings, “we now know that it had to have been after 27,000 years ago.” The results also have profound implications for present-day climate change, says Ólafur Ingólfsson, a glacial geologist at the University of Iceland in Reykjavik. “We know very little about how rapid environmental changes are in Antarctica,” he says, and yet “what happens in Antarctica will spread like ripples throughout the global system.” Emslie’s data will now allow geologists to calibrate models of past climate change and so make better climate predictions. “What Steve is doing is absolutely brilliant,” Ingólfsson says.Source