HR: 10:20h
AN: GC32A-01    [Abstracts]
TI: Climate response in the western United States to dust-shortened snow cover duration since late 1800s soil disturbance
AU: * Painter, T H
EM: painter@geog.utah.edu
AF: Department of Geography, University of Utah, Salt Lake City, UT 84112, United States
AU: Mahowald, N
EM: nmm63@cornell.edu
AF: Department of Earth and Atmospheric Sciences, Cornell University, Ithaca, NY 14853, United States
AU: Neff, J C
EM: Jason.C.Neff@Colorado.EDU
AF: Department of Geological Sciences, University of Colorado, Boulder, CO 80309, United States
AB: Dust emitted from the deserts of the western US is currently shortening snow cover duration in the Rocky Mountains by 20-35 days and affecting a Spring radiative forcing of 25 - 50 W m-2 through snow albedo reduction. With the injection of railroads and infrastructure into the interior of the western US in the mid 1800s came substantial increases grazing, farming, and mining, and in turn a disturbance of 70 percent of natural ecosystems resulting in losses of soil stability and increased dust emission. Recent geochemical analysis of alpine lake sediments in southwest Colorado shows that since the 1800s settlement of the western US, dust loading to mountain environments abruptly increased by a factor of ~5 above average rates of the last 5000 years. Given present dust loading to the Rocky Mountains and its associated forcing of snowmelt and reduction of snow cover duration, it is evident that snow cover endured significantly longer prior to the mid 1800s disturbance. In this work, we assess the climate response in the western US to the perturbed duration of mountain snow cover affected by the dramatic increase in dust loading using the NCAR Community Atmospheric Model (CAM). We drive the CAM with snow cover duration scenarios consistent with the snow albedo reductions associated with pre-1850 and post-1850 dust loadings. The 2nd indirect effect of dust loading to snow is given by the enhanced absorption of shortwave radiation by a darker substrate emerging from the early ablation of snow cover. In this region, 30 days of reduced snow cover results in mean daily 2nd indirect effect of ~ 150 W m- 2. Therefore, we hypothesize that reduced snow cover duration results in significant regional tropospheric warming, a perturbed monsoon in the southwest US, and reduced cloud cover. In turn, the historical record of hydrologic observations in these regions has likely been entirely disturbed by anthropogenic forcing.
DE: 0736 Snow (1827, 1863)
DE: 1620 Climate dynamics (0429, 3309)
DE: 1621 Cryospheric change (0776)
DE: 1631 Land/atmosphere interactions (1218, 1843, 3322)
DE: 1884 Water supply
SC: Global Environmental Change [GC]
MN: 2007 Fall Meeting