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JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 113, F02011, doi:10.1029/2007JF000883, 2008

Sensitivity of a model projection of near-surface permafrost degradation to soil column depth and representation of soil organic matter

David M. Lawrence

Climate and Global Dynamics Division, National Center for Atmospheric Research, Boulder, Colorado, USA


Andrew G. Slater

Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, Colorado, USA


Vladimir E. Romanovsky

Geophysical Institute, University of Alaska Fairbanks, Fairbanks, Alaska, USA


Dmitry J. Nicolsky

Geophysical Institute, University of Alaska Fairbanks, Fairbanks, Alaska, USA


Abstract

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 m. Together these modifications result in substantial improvements in the simulation of near-surface soil temperature in the Community Land Model (CLM). When forced off-line with archived data from a fully coupled Community Climate System Model (CCSM3) simulation of 20th century climate, the revised version of CLM produces a near-surface permafrost extent of 10.7 × 106 km2 (north of 45°N). This extent represents an improvement over the 8.5 × 106 km2 simulated in the standard model and compares reasonably with observed estimates for continuous and discontinuous permafrost area (11.2–13.5 × 106 km2). The total extent in the new model remains lower than observed because of biases in CCSM3 air temperature and/or snow depth. The rate of near-surface permafrost degradation, in response to strong simulated Arctic warming (∼ +7.5°C over Arctic land from 1900 to 2100, A1B greenhouse gas emissions scenario), is slower inthe improved version of CLM, particularly during the early 21st century (81,000 versus 111,000 km2 a−1, where a is years). 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 because of stronger near-surface vertical soil temperature gradients. This appears to lessen the sensitivity of soil temperature change to model soil depth.

Received 31 July 2007; accepted 21 February 2008; published 6 May 2008.

Keywords: permafrost; climate-change; climate model.

Index Terms: 0702 Cryosphere: Permafrost (0475); 1626 Global Change: Global climate models (3337, 4928); 1621 Global Change: Cryospheric change (0776); 1631 Global Change: Land/atmosphere interactions (1218, 1843, 3322).

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Citation: Lawrence, D. M., A. G. Slater, V. E. Romanovsky, and D. J. Nicolsky (2008), Sensitivity of a model projection of near-surface permafrost degradation to soil column depth and representation of soil organic matter, J. Geophys. Res., 113, F02011, doi:10.1029/2007JF000883.