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Study on 800-year-old tree rings backs global warming in the North American Cordillera

13.07.2011

A study on tree rings in western North America gives evidence of global warming. The study has been carried out by the U.S. Geological Survey (USGS) and University of Washington and published on Science. Scientists sampled thousands trees at 66 sites (including 800-year-old exemplars) in key runoff-generating areas of the Colorado, Columbia and Missouri River drainages. Using tree-rings chronologies, they reconstructed past snowpack levels. They discovered that unprecedented snowpack reductions occurred in the late 20th and early 21st centuries across the cordillera. The increasing role of warming on large-scale snowpack variability and trends foreshadows fundamental impacts on streamflow and water supplies in the Western USA.