The sensitivity of a model projection of near-surface permafrost degradation to soil column depth and inclusion of soil organic matter
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 modification...
| Published in: | Journal of Geophysical Research |
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| Other Authors: | , , , |
| Format: | Article in Journal/Newspaper |
| Language: | English |
| Published: |
American Geophysical Union
2008
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| Subjects: | |
| Online Access: | http://nldr.library.ucar.edu/repository/collections/OSGC-000-000-003-044 https://doi.org/10.1029/2007JF000883 |
| Summary: | 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 in the 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. |
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