After the extinction of the dinosaurs, a balmy greenhouse Earth allowed rain forests to blanket Europe and North America. Geoscientists and paleontologists recently used fossil shells to provide evidence that even Antarctica enjoyed coastal California-like temperatures from 50 to 40 million years ago. This temperate polar climate warns of what can happen when carbon dioxide builds up in the atmosphere.
Antarctic temperatures may have hit 63 degrees Fahrenheit (17 C), with an average of 57 F (14 C). Those temperatures are close to average winter temperatures in San Francisco. Parts of the southern Pacific Ocean, where temperatures now hover around freezing, warmed to 72 F (22C), similar to the waters around Florida.
Rare forms of carbon and oxygen trapped in the fossilized shells of bivalves, like oysters and mussels, allowed geologists to estimate Antarctica’s ancient climate. Measurements of the ratios of those elemental forms, or isotopes, to more common isotopes allowed the climate calculations. The Proceedings of the National Academy of Sciences published the results.
The greenhouse effect caused the Antarctic warmth. During the early Eocene Epoch, 50 million years ago, carbon dioxide levels in the air reached 700 to 900 parts per million. That’s roughly double the present concentration of 400 parts per million in March 2014, according to records from the Mauna Loa Observatory in Hawaii.
During that warm period, lemur-like primates clambered through European rainforests and cypress trees grew on Ellesmere Island in the Arctic. The new study in PNAS shows that even the coldest continent, Antarctica, thaws out when greenhouse gases reach high enough levels in the atmosphere.
“We now know that it was warm across the continent, but also that some parts were considerably warmer than others,” said geophysicist Peter M.J. Douglas, who led the research while a doctoral candidate at Yale University. “This provides strong evidence that global warming is especially pronounced close to the Earth’s poles. Warming in these regions has significant consequences for climate well beyond the high latitudes due to ocean circulation and melting of polar ice that leads to sea level rise.”
Photo: Restoration of Eocene fauna of North America, on a mural made for the Smithsonian Museum. Credit: Jay Matternes, Wikimedia Commons