Ninth International Conference on Permafrost ... - IARC Research

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Accelerated Arctic Land Warming and Permafrost DegradationDuring Rapid Sea Ice LossDavid M. LawrenceNational Center for Atmospheric Research, Boulder, CO, USAAndrew G. SlaterCooperative Institute for Research in the Environmental Sciences, Boulder, CO, USAIntroductionRobert A. Tomas, Marika M. Holland, Clara DeserNational Center for Atmospheric Research, Boulder, CO, USAIn September 2007, the annual minimum sea ice extentshattered the previous observational-record low. CRUTEM3data indicate that 2007 August to October western Arctic landtemperatures were the warmest of the last 30 years (+2.3°Cwarmer than the 1978 to 2006 average). The striking seaice decline in 2007 raises the specter that a period of abruptsea ice loss, such as those simulated in Community ClimateSystem Model (CCSM3) 21 st century A1B simulations(Holland et al. 2006), is a distinct possibility. Rapid sea iceloss events (RILEs) in CCSM3 typically last between 5 and10 years and exhibit negative sea ice extent trends that areroughly 4 times larger than average simulated (or recentlyobserved) trends.Whether or not the 2007 sea ice record minimum isa precursor of a sustained period of rapid loss remains tobe seen, but it provides motivation to assess the potentialconsequence for adjacent land climate. Here, we evaluateArctic land temperature response to RILEs in CCSM3.We find that the secular 21 st century land-warming trend isaugmented by a factor of 3.5 during RILEs, which is likelyto have adverse impacts on permafrost. Through idealizedexperiments with the Community Land Model (CLM), weassess the impact of a RILE and its timing on permafrost.The results presented here are excerpted from Lawrence etal. (2008).Arctic Land Temperature Trends DuringRapid Sea Ice LossNine RILEs are identified across the eight-memberCCSM3 A1B 21 st century ensemble (Holland et al. 2006b).By computing a lagged composite of sea ice extentanomalies across the nine events, we form a picture of thetypical sea ice extent trajectory during abrupt loss periods(Fig. 1a). A corresponding composite for western ArcticOctober to December (OND) land T airshows an increasein warming during RILEs (Fig. 1a). Figure 1b shows thewestern Arctic linear T airtrend during and outside RILEs.Warming is accelerated during RILEs throughout most ofthe year with statistically significant increases in warmingrates apparent in the summer and early autumn, likely dueto increased open water area, as well as in late autumn andwinter, when the thinner ice pack less efficiently insulatesthe atmosphere from the comparatively warm ocean waterbelow. Accelerated warming spans most of the terrestrialFigure 1. (a) Composite lagged time series of September sea iceextent (solid line) and OND T air(dashed line) over Arctic land area(65°–80°N, 60°–300°E). Composites are centered around the midpointsof the nine rapid sea ice loss events seen in the CCSM3 A1Bsimulations. Results shown as anomalies from the average of years-10 to -5. (b) Average monthly Arctic land air temperature trendsduring rapid sea ice loss periods and outside sea ice loss periods.Trend is statistically significant at the 90% (*) and 95% ( **) levels.(c) Maps of air temperature trends for OND during and outsideabrupt sea ice loss periods.western Arctic juxtaposed to the area of sea ice contractionin CCSM3. It is strongest along the Arctic coast where itis as high as 5°C decade -1 in the autumn, but a signal ofenhanced warming can extend 1500 km inland (Fig. 1c).Annually averaged, the warming trend during RILEs is 3.5times greater than outside these periods (1.60°C decade -1versus 0.46°C decade -1 ).Impact of Accelerated Warming on PermafrostTo evaluate the impact of abrupt warming and its timingon permafrost, we construct four synthetic trend scenariosbased on the results shown in Figure 1. We then use thesescenarios to force a version of CLM (Oleson et al. 2004)that includes some improvements in permafrost dynamics,namely explicit representation of the thermal and hydrologicproperties of organic soil (Lawrence & Slater 2007) and a50 m soil column that represents thermal inertia provided bydeep ground (Lawrence et al. 2008).167
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 3. Time series of depth of warming (white solid line) andcooling (white dashed line) fronts from LINEAR experiment forwarm permafrost case. Contours indicate SHC. Change in SHC isshown as black line.Figure 2. (a) Annual mean T airanomaly time series for the fourexperiments. Note that monthly air temperature anomalies used inthe forced experiments contain the annual cycle structure shownin Fig. 1c. (b) Accumulated LW↓ anomaly time series. (c) Depthto permafrost table (DPT). (d) Change in soil heat content (∆SHC)for three different initial permafrost states;soil= -0.3°C,-1.5°C, and -5.8°C from left to right.The impact of accelerated warming is shown for threeillustrative ground conditions representing differing initialpermafrost states (warm to cold) (Figs. 2c and 3d). Thesecases all exhibit minimal snow depth change (< 10%) overthe 50-yr simulation. For initially cold permafrost, thetiming of accelerated warming has little influence on therate of active layer deepening. All four scenarios simulatean ~0.35m deepening of the active layer (Table 1). However,the soil heat content (SHC) gained in EARLY (191 MJ m -2 )is 30% larger than in LATE (147 MJ m -2 ). The additional heatgained in EARLY corresponds to +0.41°C more warmingover the 50 m column. The increase in heat accumulationpreconditions permafrost for earlier and/or more rapiddegradation under continued warming.For warm permafrost, the timing of accelerated warminghas a more dramatic influence. In all four scenarios, DPTincreases slowly at first, but accelerates rapidly once a layerof perpetually unfrozen ground forms above the permafrosttable (talik) at ~2 m depth. This occurs much sooner inEARLY with accelerated warming instigating talik formationby year 12. By year 50, the warm permafrost soil column inEARLY has absorbed 900 MJ m -2 , 68% more than LATE,=yP ) 1,(TTand the DPT is 3.6 m deeper compared to only 1.9 m deeperin LATE. Why does talik formation coincide with a strongincrease in SHC accumulation rates? Taliks form when thedownwelling summer heating wave extends deeper than thecorresponding winter cooling wave, thereby preventing thetalik from refreezing in winter. Near isothermal soil layersat 0°C beneath the talik also limit cooling from below. Atthis point, with continued warming, heat accumulates atthe maximum depth of the heating wave and permafrostdegrades rapidly (Fig. 3).ReferencesHolland, M.M., Bitz, C.M. & Tremblay, B. 2006. Future abruptreductions in the summer Arctic sea ice, Geophys.Res. Lett. 33: L23503, doi:10.1029/2006GL028024.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).Lawrence, D.M., Slater, A.G., Tomas, R.A., Holland, M.M.& Deser, C. 2008. Accelerated Arctic land warmingand permafrost degradation during rapid sea ice loss.Geophys. Res. Lett. (submitted).Oleson, K.W. et al. 2004. Technical description of theCommunity Land Model (CLM). NCAR Tech. NoteTN-461+STR, 174 pp.168
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NICOP 2008 Ninth <
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ContentsPreface ...................
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Mapping and Modeling the Distributi
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Satellite Observations of Frozen Gr
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xiiIce Wedge Thermal Regime in Nort
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xivPermafrost Response to Dynamics
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NICOP SponsorsUniversitiesUniversit
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Deep Permafrost Studies at the Lupi
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Effect of Fire on Pond Dynamics in
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Cryological Status of Russian Soils
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Acoustical Surveys of Methane Plume
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Permafrost Delineation Near Fairban
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Preparatory Work for a Permanent Ge
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A Provisional Soil Map of the Trans
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Martian Permafrost Depths from Orbi
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Time Series Analyses of Active Micr
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Impact of Permafrost Degradation on
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DC Resistivity Soundings Across a P
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Modeling Thermal and Moisture Regim
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A Provisional Permafrost Map of the
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Alpine Permafrost Distribution at M
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Cryogenic Formations of the Caucasu
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Modeling Potential Climatic Change
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A Hypothesis: A Condition of Growth
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Modeled Continual Surface Water Sto
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Freeze/Thaw Properties of Tundra So
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Discontinuous Permafrost Distributi
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Thermal Regime Within an Arctic Was
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Seasonal and Interannual Variabilit
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Twelve-Year Thaw Progression Data f
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Continued Permafrost Warming in Nor
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Landsliding Following Forest Fire o
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A Permafrost Model Incorporating Dy
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Seasonal Sources of Soil Respiratio
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Greenland Permafrost Temperature Si
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The Importance of Snow Cover Evolut
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The Account of Long-Term Air Temper
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The Combined Isotopic Analysis of L
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Adaptating and Managing Nunavik’s
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Human Experience of Cryospheric Cha
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HiRISE Observations of Fractured Mo
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A Soil Freeze-Thaw Model Through th
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Mapping and Modeling the Distributi
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First Results of Ground Surface Tem
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Historical Changes in the Seasonall
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Rock Glaciers in the Kåfjord Area,
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Snowpack Evolution on Permafrost, N
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Climate Change in Permafrost Region
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Maximizing Construction Season in a
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Pleistocene Sand-Wedge, Composite-W
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