BBC: Although Earth is currently experiencing a period of global warming, it’s not the first time. The warmest global climates occurred some 48 million to 55 million years ago, during the early Eocene epoch. According to a study published in Nature yesterday, the Antarctic had a subtropical climate during the Eocene. Global temperatures were about 5 °C higher than they are today, and atmospheric CO₂ concentrations were much higher, at least 600 parts per million, compared with the current 390 ppm. The findings are the result of studying soil samples collected from Antarctica’s eastern coast. According to one of the study’s coauthors, James Bendle of the University of Glasgow, scientists are starting to take a “back to the future” approach to study climate change. Instead of relying entirely on physics-based models, they are beginning to compare and contrast episodes in the geological past with the present in order to visualize the future.