Dec 1, 2008

Attribution of Declining Western U.S. Snowpack to Human Effects

David W. Pierce, Tim P. Barnett, Hugo G. Hidalgo, Tapash Das, Céline Bonfils, Benjamin D. Santer, Govindasamy Bala, Michael D. Dettinger, Daniel R. Cayan, Art Mirin, Andrew W. Wood, and Toru Nozawa
American Meteorological Society
  • Observations show snowpack has declined across much of the western United States over the period 1950–99
  • Performs a formal model-based detection and attribution (D–A) study of these reductions
  • States that the detection variable is the ratio of 1 April snow water equivalent (SWE) to water-year-to-date precipitation (P), chosen to reduce the effect of P variability on the results
  • Obtains estimates of natural internal climate variability from 1600 years of two control simulations performed with fully coupled ocean–atmosphere climate models
  • Takes estimates of the SWE/P response to anthropogenic greenhouse gases, ozone, and some aerosols are taken from multiple-member ensembles of perturbation experiments run with two models
  • The D–A shows the observations and anthropogenically forced models have greater SWE/P reductions than can be explained by natural internal climate variability alone
  • Finds that model-estimated effects of changes in solar and volcanic forcing likewise do not explain the SWE/P reductions
  • Finds that the mean model estimate is that about half of the SWE/P reductions observed in the west from 1950 to 1999 are the result of climate changes forced by anthropogenic greenhouse gases, ozone, and aerosols