Abstract

Paleoclimatology is the study of past climate. While in rare cases we may be able to study past climate from “directly observed” historical record, typically we infer past climate indirectly through the use of proxies. These proxies, such as tree rings, ice cores, corals, and pollen, have climate-sensitive characteristics that can be measured (e.g., tree ring density; the ratio of dissolved oxygen isotopes in ice cores and coral; the signature and relative abundance of pollen species). By associating these climate sensitive measurements to observed instrumental records of climate such as temperature and precipitation, we are able to predict or hindcast past climate along with, hopefully, an associated measure of uncertainty for our predictions. This task is called paleoclimate reconstruction. For example, tree ring densities of certain species of trees in the upper latitudes, suitably normalized to remove growth effects, are approximately linearly associated with temperature. By modeling the relationship between tree ring density and observed temperature, we can produce predictions of past temperature.