Antarctica, today a continent of forever frozen tundra, once boasted a climate more similar to that of the coastline of today's Northern California, a study has shown.
In addition, the surrounding southern Pacific Ocean once had temperatures on par with those recorded in Florida waters in this century, researchers say.
Yale University scientists led a study of the Eocene era in Antarctica from 40 million to around 50 million years in the past, when elevated concentrations of carbon dioxide in the atmosphere created what we today would consider a greenhouse-type climate.
The study shows the frozen continent wasn't always what it is today, the coldest place on Earth for most of the year with average temperatures staying below zero.
Examining carbon and oxygen in fossil shells gathered from a small island off the Antarctic coast, the researchers could pin temperatures those many million of years ago at an average of 57 degrees Fahrenheit, while water in the surrounding ocean averaged 72 degrees Fahrenheit, just like coastal waters around Florida today.
The finding can help scientists improve their climate models used for predicting future world climate, they said.
"Quantifying past temperatures helps us understand the sensitivity of the climate system to greenhouse gases, and especially the amplification of global warming in polar regions," Yale geophysics and geology Professor Hagit Affeck said.
Ocean waters around Antarctica were not uniform, the researchers found -- the South Pacific edge of the continent was warmer -- suggesting ocean currents were creating temperature differences.
"By measuring past temperatures in different parts of Antarctica, this study gives us a clearer perspective of just how warm Antarctica was when the Earth's atmosphere contained much more CO2 than it does today," Peter M.J. Douglas, the study's lead author, said.
"We now know that it was warm across the continent, but also that some parts were considerably warmer than others," he explains. "This provides strong evidence that global warming is especially pronounced close to the Earth's poles."
The researchers say knowledge of how the climate of Antarctica has changed with time will help in understanding and predicting the climate impacts of global warming.
"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," Douglas says.
The study has been published in the Proceedings of the National Academy of Science.