| Abstract: | ![]()
Conceptual climate models, based on the workings of the present-day climate system, provided a first-order approach to ancient climate systems. They are potentially very subjective in character. Their main drawback was that they involved the relocation of continents beneath a stable atmospheric circulation modelled upon that of the present. General circulation models (GCMs) use the laws of physics and an understanding of past geography to simulate climatic responses. They are objective in character. However, they require super computers to handle vast numbers of calculations. Nonetheless it is now possible to compare results from different GCMs for a range of times and over a wide range of parameterisations. GCMs are currently producing simulated climate predictions which compare favourably with the distributions of climatically sensitive facies (e.g. coals, evaporites and palaeosols). They have been used effectively in the prediction of oceanic upwelling sites and the distribution of petroleum source-rocks and phosphorites. Parameterisation is the main weakness in GCMs (e.g. sea-surface temperature, orography, cloud behaviour). Sensitivity experiments can be run on GCMs which simulate the effects of Milankovitch forcing and thus provide insights into possible patterns of climate change both globally and locally (i.e. provide predictions that can be evaluated against the rock record). Future use of GCMs could be in the forward modelling of sequence stratigraphic evolution and in the prediction of the diagenetic characteristics of reservoir units in frontier exploration areas. The sedimentary record provides the only way that GCMs may themselves be evaluated and this is important because these same GCMs are being used currently to predict possible changes in future climate. |
