Improved proxy record of past warm climates needed

Before the end of the present century, atmospheric carbon dioxide (CO2) is projected to reach the high levels last seen in past warm periods such as the Eocene (˜40 million years ago) [Beerling and Royer, 2011]. Climate reconstructions from sediment cores (“proxy data”) and paleoclimate modeling studies show that such higher CO2 periods are characterized by warmer temperatures, smaller ice sheets, and higher sea level than today. The proxy record of past warm climates is thus fundamental in guiding scientists' understanding of future climate changes. However, we believe that currently available data sets are not yet adequate for this task.