The question seems simple enough: What happens to the Earth’s temperature when atmospheric carbon dioxide levels increase? It has happened in the past. The answer is elusive. However, clues are hidden in the fossil record. A new study by researchers from Syracuse and Yale universities provides a much clearer picture of the Earth’s temperature approximately 50 million years ago when CO2 concentrations were higher than today. The results may shed light on what to expect in the future if CO2 levels keep rising. The study which for the first time compared multiple geochemical and temperature proxies to determine mean annual and seasonal temperatures, is published online in the journal Geology, the premier publication of the Geological Society of America, and will be published in print on August 1.