New (and better) tree ring analysis shows climate change effects

Despite odd years like this one, researchers have long reported declines in the mountain snows that power Western rivers. But on Thursday a group of scientists said they now also know this: Those declines are virtually unprecedented throughout most of the last millennium.

Scientists from the U.S. Geological Survey (USGS) and University of Washington measured tree-ring growth from forests that included 800-year-old trees. They learned that snowpack reductions in the late 20th and early 21st centuries were unlike any other period dating to at least the year 1200, according to new research published in the journal Science.

The precise amount of those declines, particularly in the Cascades, has been the subject of fierce debate even within UW climate circles. But no more than half of the declines can be explained by natural shifts, the study shows.