Ninth International Conference on Permafrost ... - IARC Research

Ni n t h In t e r n at i o n a l Co n f e r e n c e o n Pe r m a f r o s tFigure 1. Annual cycle-depth plots of soil temperature averaged forselected stations in Russian soil temperature dataset (Zhang et al.2001). Stations include those that exhibit perpetually frozen soil intop 3 m. Equivalent locations extracted and averaged over the sametime period from offline CLM simulations forced with observeddata.Figure 2. Time series of total area containing near-surface permafrost(north of 45°N and excluding ground underneath glaciers) forselected experiments.CONTROL CCSM3and CONTROL CLM3are not shown for thesake of clarity, but lie roughly in between the curves forCONTROL and SOILCARB. As noted above, experimentsthat include soil organic matter are substantially cooler, andnear-surface permafrost extent is correspondingly broader.The observed estimates for the area of continuous permafrost(90–100% coverage) and discontinuous permafrost (50–90% coverage) combined are 11.2–13.5 million km 2 (for theregion poleward of 45°N (Zhang et al. 2000). The total areasimulated in CONTROL is clearly biased low at 8.5 millionkm 2 . In the organic soil and deeper soil column experiments,the area with near-surface permafrost increases to 10.5 and10.7 million km 2 , respectively, which compares reasonablywith the observed permafrost extent although still biased alittle low.The rate of near-surface permafrost extent contraction isslower between 1990 and 2040 in SOILCARB (87,000 km 2yr -1 versus 111,000 km 2 yr -1 in SOILCARB and CONTROL,respectively). In simulations with a deeper soil column, theaverage rate of loss decreases further to 81,000 km 2 yr -1 and76,000 km 2 yr -1 (1990–2040) in SOILCARB_DS50 andSOILCARB_DS125. However, even though near-surfacepermafrost degrades at a slower rate in the latter threeexperiments, the total degradation by 2100 is almost asextensive as that seen in CONTROL.Although much of the simulated near-surface permafrostdegrades in all experiments, it should be stressed that thisdoes not mean that all permafrost disappears. As notedabove, each grid box is represented by a single soil columnwhich means that sporadic and isolated permafrost cannotbe explicitly detected in the model. For regions wherethe maximum soil temperature rises above 0°C, but onlymarginally, it can be assumed that sporadic or isolatedpatches of permafrost would still be present in the warmerclimate. Additionally, for the deep soil experiments, we findthat most of the deep permafrost remains at the end of the21 st century.ReferencesAlexeev, V.A., Nicolsky, D.J., Romanovsky, V.E. &Lawrence, D.M. 2007. An evaluation of deepsoil configurations in the CLM3 for improvedrepresentation of permafrost. Geophys. Res. Lett. 34:L09502, doi:10.1029/2007GL029536.Lawrence, D.M. & Slater, A.G. 2005. A projection ofsevere near-surface permafrost degradation duringthe 21st century. Geophys. Res. Lett. 24: L24401,doi:10.1029/2005GL025080.Lawrence, D.M. & Slater A.G. 2007. Incorporatingorganic soil into a global climate model, Clim. Dyn.doi:10.1007/s00382-007-0278-1.Lawrence, D.M., Slater, A.G., Romanovsky, V.E. & Nicolsky,D.J. 2008. The sensitivity of a model projection ofnear-surface permafrost degradation to soil columndepth and representation of soil organic matter. JGR-Earth Surface (in press).Nicolsky, D.J., Romanovsky, V.E., Alexeev, V.A. & Lawrence,D.M. 2007. Improved modeling of permafrostdynamics in a GCM land-surface scheme, Geophys.Res. Lett. 34: L08501, doi:10.1029/2007GL029525.Oleson, K.W. et al. 2004. Technical description of theCommunity Land Model (CLM). NCAR Tech. NoteTN-461+STR, 174 pp.170