What was the climate like when the earth was warmer than it is today? To find the answer, researchers in a group called Pliocene Research, Interpretation and Synoptic Mapping (PRISM) are trying to reconstruct a warm period that existed 3 million years ago.

Led by the U.S. Geological Survey (USGS), scientists are examining fossils from the Pliocene Epoch when temperatures were 4 degrees Fahrenheit warmer than today and within the range projected for the 21st century by the Intergovernmental Panel on Climate Change. The fossils indicate the temperatures of the sea surface and the deepwater ocean.

The researchers will also be looking at carbon dioxide (CO2) levels then and now. According to a press release from the USGS, they believe that levels were “only slightly higher than today’s levels.” Their data suggests that warmth in the Pliocene period was a combination of several factors, including increased heat transport from equatorial regions to the poles and increased greenhouse gases.  

 The primary goal of the PRISM project is to create three-dimensional global data sets of Pliocene conditions, which will form the most comprehensive global reconstruction for any warm period prior to the recent past.