Whether the last ice age was unusually chilly is more than merely historical curiosity. Such information is used to bench mark the computer models that are used to estimate future greenhouse warming. In his Perspective, Bard discusses recent efforts to use geochemical data to calculate past climate behavior. Data from noble gases in groundwater and trace elements in corals, for example, can indicate past sea surface temperatures. This can be compared with general circulation models, a comparison that shows good progress in modeling and also highlights where improvements can be made. According to the author, these advances have been made possible by the extensive exchanges of information between the data measurement and the modeling communities.
