Antarctica was once as warm as Iceland - warm enough for vegetation and even trees to thrive, a new study has found.
An examination of plant leaf wax remnants in sediment core samples taken from beneath the Ross Ice Shelf has shown that summer temperatures along the Antarctic coast 15 to 20 million years ago were 20 degrees Fahrenheit warmer than today, sometimes hitting as high as 45 degrees.
Precipitation levels also were found to be several times higher than today.
"The ultimate goal of the study was to better understand what the future of climate change may look like," says Sarah Feakins, an assistant professor of Earth sciences at the USC Dornsife College of Letters, Arts and Sciences.
"Just as history has a lot to teach us about the future, so does past climate. This record shows us how much warmer and wetter it can get around the Antarctic ice sheet as the climate system heats up. This is some of the first evidence of just how much warmer it was."
Scientists had begun to suspect that this was the case following the discovery of pollen and algae in sediment cores taken around Antarctica. But it's been hard to check, as the movement of ice sheets scrapes away any evidence.
"Marine sediment cores are ideal to look for clues of past vegetation, as the fossils deposited are protected from ice sheet advances, but these are technically very difficult to acquire in the Antarctic and require international collaboration," says Warny.
Feakins opted to examine sediment cores for the remnants of leaf wax, which acts as a record of climate change by documenting the hydrogen isotope ratios of the water the plant took up while it was alive. The team used a model originally developed to analyze atmospheric water vapor data from NASA's Aura spacecraft.
"When the planet heats up, the biggest changes are seen toward the poles," says NASA scientist Jung-Eun Lee. "The southward movement of rain bands associated with a warmer climate in the high-latitude southern hemisphere made the margins of Antarctica less like a polar desert, and more like present-day Iceland."
The peak of this Antarctic greening occurred during the middle Miocene period, between 16.4 and 15.7 million years ago. The warm conditions are thought to be associated with carbon dioxide levels of around 400 to 600 parts per million (ppm). For comparison, the current level is 393 ppm, the highest for several million years.
At the current rate of increase, atmospheric carbon dioxide levels are set to reach middle Miocene levels by the end of this century.