Storm activity in ancient climates 1. Sensitivity of severe storms to climate forcing factors on geologic timescales

Severe storms are important agents of sediment transport, and they generate sedimentary structures and textures that can be identified in the geologic record. The genesis and the distribution of storms are associated with distinctive meteorological controls, which in many cases lend themselves to analysis using general circulation models of the atmosphere. The goal of this study is to predict the distribution of severe storms in Earth history and to evaluate the correspondence between climate model predictions and geologic observations for widely different past climate conditions. The first step toward achieving this goal is an assessment of the importance of different climatic forcing factors, including paleogeography, topography, solar luminosity, carbon dioxide concentrations, and ocean heat transport variations. This assessment is based on sensitivity experiments using the GENESIS general circulation model. Paleogeography plays the most important role in governing the distribution of winter storms and plays a major role in hurricane genesis and steering. In contrast, changes in carbon dioxide, ocean heat transport, and solar luminosity exhibit little influence on the distribution of winter storms or the steering of hurricanes. However, these factors influence the strength of winter storms and the area and frequency of hurricane generation. The relationships between climatic forcing factors and storm genesis and distribution provide considerable guidance in comparisons of model predictions with observations of severe storms in Earth history and for the interpretations of storm deposits. The comparison of model predictions to the geologic record is the subject PSUCLIM 2 [this issue].