Scientists have claimed that parts of ancient Antarctica were as warm as today's California coast, using a new way to measure past temperatures.
And polar regions of the southern Pacific Ocean registered 21st-century Florida heat. The findings underscore the potential for increased warmth at Earth's poles and the associated risk of melting polar ice and rising sea levels, the researchers said.
Led by scientists at Yale, the study focused on Antarctica during the Eocene epoch, 40-50 million years ago, a period with high concentrations of atmospheric CO2 and consequently a greenhouse climate.
Today, Antarctica is year-round one of the coldest places on Earth, and the continent's interior is the coldest place, with annual average land temperatures far below zero degrees Fahrenheit.
But it wasn't always that way, and the new measurements can help improve climate models used for predicting future climate, according to co-author Hagit Affek of Yale, associate professor of geology and geophysics.
"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," Affek said.
By measuring concentrations of rare isotopes in ancient fossil shells, the scientists found that temperatures in parts of Antarctica reached as high as 17 degrees Celsius (63F) during the Eocene, with an average of 14 degrees Celsius (57F) - similar to the average annual temperature off the coast of California today.
Eocene temperatures in parts of the southern Pacific Ocean measured 22 degrees Centigrade (or about 72F), researchers said - similar to seawater temperatures near Florida today.
Today the average annual South Pacific sea temperature near Antarctica is about 0 degrees Celsius.
These ancient ocean temperatures were not uniformly distributed throughout the Antarctic ocean regions - they were higher on the South Pacific side of Antarctica - and researchers say this finding suggests that ocean currents led to a temperature difference.
The research is published in the Proceedings of the National Academy of Sciences.