HR: 11:20h
AN: C32A-05    [Abstracts]
TI: Modeling permafrost and permafrost-related climate-change feedbacks in a GCM: Sensitivity to soil column depth and representation of soil organic matter
AU: * Lawrence, D
EM: dlawren@ucar.edu
AF: National Center for Atmospheric Research, P.O.Box 3000, Boulder, CO 80307,
AU: Slater, A
EM: aslater@cires.colorado.edu
AF: National Snow and Ice Data Center, University of Colorado, Boulder, CO 80309,
AB: The sensitivity of a global land-surface model projection of near-surface permafrost degradation is assessed with respect to explicit accounting of the thermal and hydrologic properties of soil organic matter and to a deepening of the soil column from 3.5 to 50 or more meters. Together, these modifications result in substantial improvements in the simulation of near-surface soil temperature in the NCAR Community Land Model (CLM) which is the land surface model for the Community Climate System Model (CCSM) and the Community Atmosphere Model (CAM). When forced offline with archived data from a fully coupled CCSM simulation of 20th century climate, the revised version of CLM produces a near-surface permafrost extent (10.7 million km2 north of 45°N) that is improved over the standard model (8.5 million km2) and compares reasonably (although still biased low possibly due to biases in soil temperature caused by CCSM3 air temperature and/or snow depth biases) with observed estimates for continuous and discontinuous permafrost area (11.2-13.5 million km2). The rate of near-surface permafrost degradation, in response to the strong simulated Arctic warming (~ +7.5°C over Arctic land, 1900 - 2100; A1B greenhouse gas emissions scenario), is slower in the improved version of CLM, particularly during the early 21st century (81,000 km2 yr-1 versus 111,000 km2 yr-1). Even at the depressed rate, however, the warming is enough to drive near-surface permafrost extent sharply down by 2100. Experiments with a deep soil column exhibit a larger increase in ground heat flux than those without due to stronger near-surface vertical soil temperature gradients. This appears to lessen the sensitivity of soil temperature change to soil depth. Additional improvements to and features of CLM that are relevant to permafrost degradation related climate- change feedbacks will also be reviewed including those to snow, wetlands and lakes, carbon-nitrogen cycling, and dynamic vegetation biogeography.
DE: 0702 Permafrost (0475)
DE: 1626 Global climate models (3337, 4928)
SC: Cryosphere [C]
MN: 2007 Fall Meeting