Climate change that predates the instrumental period of direct weather observations is known as palaeoclimate change. Palaeoclimatology provides a longer perspective on climate variability that can improve our understanding of the climate system, and help us to predict future climatic changes as a result of man-made global warming. Evidence for palaeoclimatic change can be obtained by the study of natural phenomena which are climate-dependent. Such evidence comes from palaeoclimatic records.
Many natural systems are dependent on climate. From these it may be possible to derive palaeoclimatic information for variables such as temperature or rainfall. Such proxy or indirect records of climate contain a climatic signal. Deciphering that signal is often a complex business. Four types of palaeoclimatic record are commonly analysed for past climate variations. These include historical records, glaciological records (for example ice cores), biological records (for example tree rings), and geological records (for example ocean sediments).
The suitability of a particular palaeoclimatic record for reconstructing a past climate will be largely dependent upon the time scale of past climate change under study. Recent climate changes during the last few thousand years can be reliably reconstructed from tree ring analyses, which often yield continuous records and provide high-resolution (annual or even seasonal) data. Over the longer term, ice cores and sea sediments offer information about palaeoclimates stretching back hundreds of thousands of years, although the data resolution may not be as fine. Generally, the further back in time we go the greater the margins of uncertainty that will be attached to palaeoclimatic reconstructions.