The levels of snowpack in the mountains in the Western United States have a substantial impact upon the local natural environment. This is due to the fact that increased runoff impacts temperature due to the loss of capacity of snow and ice to reflect heat back into the atmosphere – the so-called "albedo feedback." This in turn influences a wide range of ecosystem processes.
It has been reported that snowpack in the Western United States has experienced a noticeable decline in recent decades. Weather projections predict that this decline will continue to increase in the twenty-first century. In order to quantify these changes Dr. Gregory T. Pederson and his colleagues from the U.S Geological Survey (USGS) at the Northern Rocky Mountain Science Center in Bozeman, Montana have developed snowpack reconstructions for the headwaters of the Columbia, Missouri and Colorado Rivers. These reconstructions examine levels of snowpack that span from five hundred to a thousand years. These findings are based upon an "extensive network of tree-ring sites," and elucidate patterns of water management and snow accumulations over extended periods of time. The study of tree-rings has long been utilized to reconstruct patterns in regard to precipitation, drought and temperature. Previous studies have clearly demonstrated that the amount of water available to trees during their growing cycle is largely dependent on the amount of snowpack that accumulated during prior winter seasons.
As a result of the data accumulated during this investigation, the author concluded that, "Over the past millennium, late 20th century snowpack reductions are almost unprecedented in magnitude across the northern Rocky Mountains." This is a matter of serious concern in that it may well be a harbinger of future conditions of drought and establishes further relationships between the accumulation of greenhouse gases in the atmosphere, temperature and the global water cycle.