It's the question at the heart of the climate change story - just how does the Earth's temperature react to increased levels of CO2? Researchers from two American universities have looked for an answer in the fossils from a time, 50 million years ago, when CO2 levels were much higher than they are today.
The Syracuse and Yale team published their results in the journal Geology, the premier publication of the Geological Society of America, online now and in print from August 1.
"The early Eocene Epoch (50 million years ago) was about as warm as the Earth has been over the past 65 million years, since the extinction of the dinosaurs," said Linda Ivany, associate professor of earth sciences.
"There were crocodiles above the Arctic Circle and palm trees in Alaska. The questions we are trying to answer are how much warmer was it at different latitudes and how can that information be used to project future temperatures based on what we know about CO2 levels?"
Scientists already knew that the Polar Regions at the time were warm but have had little date from lower latitudes to confirm the assumption that they must have been warmer still.
Now, the team believe the average temperature in the US Gulf Coast region was around 27 degrees centigrade (80 degrees Fahrenheit), currently it's around 75 degrees Fahrenheit. Seasonal temperature changes were much lower in the Eocene.
The team studied growth rings in the shells of molluscs and tested other material found in the fossils.
Top Image Credit: Fossils © pdtnc