CALIBRATION OF A GLACIER MODEL TO HISTORIC VARIATIONS OF THE TETON GLACIER TO IMPROVE MODEL-BASED INFERENCES ABOUT GLACIER – CLIMATE RELATIONSHIPS

The Teton Range and the Wind River Range of northern Wyoming both preserve dramatic evidence of the last ice age in the form of extensive moraine complexes and high trimlines. Indeed, the Wind River range is the type locale for much of the Northern Rocky mountain glacial sequence. In addition, both of these ranges still contain significant glaciers in high mountain cirques. To estimate the climatic shifts associated with past glacial stages in those ranges, and the likely effects of predicted regional warming on their extant glaciers, we have developed models at several different scales using a general purpose 2-D numerical glacier simulator. The simulator includes a detailed treatment of effects high-relief topography on net radiation, a physically-based treatment of the other components of the surface energy balance and a transient solution to a set of non-linear equations describing 2-D ice flow.

Uncertainties in conclusions based on such modeling are, in part, due to the fact that calibration data are often very limited. In this study, we use a long sequence of historical photos of the Teton Glacier, combined with meteorological records dating back to the early 1900's, to demonstrate how the model can be calibrated via adjustments to match a time-sequence of glacial changes. In addition to improving confidence in model-based inferences about paleoclimates, the process also illustrates the importance of considering response time in making inferences about climate from changes in glacier length. Glaciers of different size and aspect can have significantly different responses to temperature variations, to the extent that modern recessions may not, for example, reflect modern warming.

While our emphasis here is on testing the model's ability to simulate observed glacier changes at relatively high resolution, we also present simulation results that describe a range of climatic conditions that could have produced Pinedale-age glaciers in both ranges, and – based on simulations of reputed Younger Dryas deposits in the Wind River range – predict where similar deposits should be present in the Tetons. Lastly, we illustrate how specific glaciers in both ranges might be expected to retreat in response to predicted regional warming during the next 50 years.