ABSTRACT
The reconstructions that have been made of the last ice age have provided much information on past climatic conditions. The most unified attempt has been in the CLIMAP Project (CLIMAP Project Members 1976) where detailed reconstructions were made for the Earth's climate for 18,000 BP. More recently, several attempts have been made to develop numerical models of the patterns of global oceanic and atmospheric circulation that existed during the last ice age. These general circulation models (GCMs) represent simulations, based on geological evidence, of the response of the atmosphere to inferred distributions of sea surface temperature, the extent and altitude of former ice sheets, the former distribution of lakes, etc. The GCMs are then tested by the use of other climate parameters not used in the model (e.g. land-based estimates of former temperatures). During recent years, numerous GCMs have been developed, each different from each other and each providing different results. A particular difficulty has been that the geological evidence of past environmental conditions in different areas of the world is highly controversial. Thus the accuracy of individual GCMs is only as reliable as the geological data that are used in the construction of the respective models.
