Physical controls on the sensitivity of snow and ice to climate change: Orographic precipitation, dynamic thinning and basal sliding.

摘要

With implications ranging from water resource scarcity to sea level rise, understanding the response of the Earth's snow and ice cover to ongoing climate change is critical for assessing the sustainability of human infrastructure. However, current models of this sensitivity are incomplete in their treatment of important physical processes. Three of the least understood, but most critical, controls on glacier and snowpack response to climate are the enhancement of orographic precipitation during warming, the mechanics of rapid glacier thinning and the hydraulic controls on glacier sliding. The objective of this work is to improve the fundamental understanding of these processes through integration of observations and empirical and analytical models.; In California, climate models predict that 2-3°C of greenhouse-driven warming over the next century will lead to an over 60% decrease in spring snowpack. However, despite several degrees of warming over the past 50 years, there has been little change in summer river discharge and continued expansions of Mt. Shasta's glaciers. Using the historical records of snow water equivalent, climate and glacier size, the relationship between climate and snow and ice volume is explored through a host of statistical and physical methods. These analyses suggest that, likely due to orographic enhancement and ocean proximity, precipitation is the dominant driver of snow and ice mass balance in California.; Accelerated coastal thinning of the Greenland Ice Sheet over the past decade exceeds surface melting and has raised concern over a dynamic feedback between thinning and ice velocity. Using remote sensing methods, coordinated thinning, acceleration and retreat over the past five years is observed at Helheim Glacier. These data suggest that acceleration results from increased longitudinal stress gradient and driving stress during front retreat, likely initiated by surface thinning.; Three-dimensional surface motion is used as a proxy of changes in subglacial water storage and cavitation during sliding at Breithamerkurjokull, Iceland. The relation between sliding and inferred storage suggests that sliding is controlled by the area expansion and contraction of subglacial cavities. This is hypothesized in a new sliding law that accounts for the often-observed hysteresis between sliding speed and water pressure.