the post I made, right above yours... go ahead, read it. Here's part of the conclusion from it:
SWE = Snow Water Equivalent or how much water there is in the snowpack... it's what is important to most of the people studying this because of it's impacts on the water supply of many areas of the world. You can basically think of it as more SWE = more snow, less SWE = less snow.
CONCLUSION:
Widespread declines in springtime SWE have occurred in much of the North American West over the period 1925–2000, especially since midcentury. While nonclimatic factors like growth of forest canopy might be partly responsible, several factors argue for a predominantly climatic role: the consistency of spatial patterns with climatic trends, the elevational dependence of trends, and, most important, the broad agreement with the VIC simulation.
...
We are left, then, with the most important question: Are these trends in SWE an indication of future directions? The increases in temperature over the West are consistent with rising greenhouse gases, and will almost certainly continue (Cubasch et al. 2001). Estimates of future warming rates for the West are in the range of 2°–5°C over the next century, whereas projected changes in precipitation are inconsistent as to sign and the average changes are near zero (Cubasch et al. 2001). It is therefore likely that the losses in snowpack observed to date will continue and even accelerate (Hamlet and Lettenmaier 1999a; Payne et al. 2004), with faster losses in milder climates like the Cascades and the slowest losses in the high peaks of the northern Rockies and southern Sierra. Indeed, the agreement in many details between observed changes in SWE and simulated future changes is striking and leads us to answer the question at the beginning of this paragraph in the affirmative. It is becoming ever clearer that these projected declines in SWE, which are already well underway, will have profound consequences for water use in a region already contending with the clash between rising demands and increasing allocations of water for endangered fish and wildlife.
TL;DR There is scientific proof of a declining snowpack in Western North America and it's pretty damn well accepted among scientists who specialize in this area.