Greg Pederson on Glaciers and Snowpack

Greg Pederson, an ecologist with the U.S. Geological Survey in Bozeman, Montana, works hard to understand the ways in which the West's climate is changing by studying glaciers and snowpack.  After a decade of work on the ground - much of it in Montana's Crown of the Continent - he has spent countless hours in the field and published over two dozen scientific papers.

This past summer, Greg and a group of his fellow scientists discovered that snowpack in the northern and southern Rocky Mountains over the past 30 years is substantially lower than average snowpack levels over the past thousand years (see link to study at right).

This is big news for the 70 million people who get their drinking water from the the headwaters of the Columbia, Missouri, and Colorado Rivers, because 60-80% of that water comes from melting snow every year.

And how do these scientists know what the snowpack looked like over the past 1,000 years?

They measured tree-ring growth from forests that included 800-year old trees across the Western United States and up into Canada.

Tree rings allow researchers to reconstruct snow levels in the past in two different ways:

  • At low elevations, ponderosa pine and Douglas fir have wider growth rings during years of heavy snowfall because more water is available.
  • At higher elevations, subalpine larch and hemlock trees have the opposite pattern: they have thinner growth rings during years when snowfall is heavy because the deep snow takes longer to melt, resulting in a shorter growth season.

This study provides crucial information to water managers in the West, and highlights the serious consequences that continuing decline in snowpack - driven by warmer temperatures throughout the West - could have on drinking water supplies for many people.

Photo, at top of page:  U.S. Geological Survey