MSGID: 1:317/3 63f59a74   
   PID: hpt/lnx 1.9.0-cur 2019-01-08   
   TID: hpt/lnx 1.9.0-cur 2019-01-08   
    Sinking tundra surface unlikely to trigger runaway permafrost thaw   
      
      
     Date:   
         February 21, 2023   
     Source:   
         DOE/Oak Ridge National Laboratory   
     Summary:   
         Scientists set out to address one of the biggest uncertainties   
         about how carbon-rich permafrost will respond to gradual sinking   
         of the land surface as temperatures rise. Using a high-performance   
         computer simulation, the research team found that soil subsidence   
         is unlikely to cause rampant thawing in the future.   
      
      
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   FULL STORY   
   ==========================================================================   
   Oak Ridge National Laboratory scientists set out to address one of the   
   biggest uncertainties about how carbon-rich permafrost will respond   
   to gradual sinking of the land surface as temperatures rise. Using a   
   high-performance computer simulation, the research team found that soil   
   subsidence is unlikely to cause rampant thawing in the future.   
      
      
   ==========================================================================   
   This permanently frozen landscape in the Arctic tundra, which has kept   
   vast amounts of carbon locked away for thousands of years, is at risk   
   of thawing and releasing greenhouse gases into the atmosphere.   
      
   The United Nation's Intergovernmental Panel on Climate Change has   
   identified the possibility of soil subsidence leading to a feedback   
   loop that could trigger a rapid thaw as a major concern in the decades   
   ahead. Accelerated thawing caused by uneven land subsidence has been   
   observed on smaller scales over shorter time frames, but the IPCC's   
   assessments were uncertain as to what may happen over the long term.   
      
   That's where ORNL stepped in with its Advanced Terrestrial Simulator,   
   or ATS, a highly accurate, physics-based model of the region's hydrology   
   fed by detailed, real-world measurements to help scientists understand   
   the land's evolution.   
      
   What they found is that even though the ground will continue to sink   
   as big ice deposits melt, the uneven subsidence also leads to a drier   
   landscape and limits the process's acceleration through the end of   
   the century, as described in the Proceedings of the National Academy   
   of Sciences.   
      
   "Improved drainage results in a drier landscape over a decadal timescale,   
   and the process then becomes self-limiting," said Scott Painter, who   
   leads the Watershed Systems Modeling group at ORNL.   
      
   The scientists focused on a large region of the tundra characterized   
   by ice wedges -- long pieces of ice that crack the surface and extend   
   belowground to create polygonal forms in the Arctic landscape. The   
   cryo-hydrology simulations were informed by measurements gathered in   
   the polygonal tundra.   
      
   The ATS was first developed for the Department of Energy's NGEE Arctic   
   project led by ORNL, focused on observations, experiments and modeling   
   of the environmental processes at play in the region to improve climate   
   predictions.   
      
   "We looked at the microtopography caused by these ice wedges in the   
   subsurface and how that controls the flow of water," Painter said. "Ours   
   is the first capability to capture the effect of changing microtopography   
   and represent it in climate models."  Painter added that the team has   
   a high degree of confidence in the model since it was developed for   
   NGEE Arctic and has been evaluated against the project's real-world   
   observations.   
      
   He noted that most models, including ORNL's, are in agreement in   
   generally projecting large amounts of carbon thaw in the Arctic as   
   temperatures rise.   
      
   "But here, we have identified that one of the most worrisome processes,   
   this runaway thawing due to subsidence, is unlikely to occur over a   
   long time frame."  The study pointed out other implications of a drying   
   landscape. "As the polygonal tundra gets very dry, by the year 2100   
   it could have ecological impacts for migratory birds, which use these   
   ecosystems as breeding grounds," Painter said.   
      
   Other scientists collaborating on the study include ORNL's Ethan Coon;   
   Ahmad Jan, formerly of ORNL and now at the NOAA-affiliated Office of   
   Water Prediction; and Julie Jastrow of Argonne National Laboratory.   
      
   The research was supported by NGEE Arctic, which is sponsored by the   
   DOE Office of Science's Biological and Environmental Research Program   
   and led by ORNL, and BER's Environmental System Science Program at   
   Argonne. NGEE Arctic supported the original development of ATS as well   
   as recent enhancements to incorporate subsidence into the model.   
      
       * RELATED_TOPICS   
             o Earth_&_Climate   
                   # Tundra # Climate # Global_Warming # Weather #   
                   Earth_Science # Environmental_Issues # Snow_and_Avalanches   
                   # Environmental_Policy   
       * RELATED_TERMS   
             o Computer_simulation o Global_warming o Tundra o Forest o   
             Climate_model o Earth_science o Carbon_cycle o Surface_runoff   
      
   ==========================================================================   
   Story Source: Materials provided by   
   DOE/Oak_Ridge_National_Laboratory. Original written by Stephanie   
   Seay. Note: Content may be edited for style and length.   
      
      
   ==========================================================================   
   Journal Reference:   
      1. Scott L. Painter, Ethan T. Coon, Ahmad Jan Khattak, Julie   
      D. Jastrow.   
      
         Drying of tundra landscapes will limit subsidence-induced   
         acceleration of permafrost thaw. Proceedings of the National   
         Academy of Sciences, 2023; 120 (8) DOI: 10.1073/pnas.2212171120   
   ==========================================================================   
      
   Link to news story:   
   https://www.sciencedaily.com/releases/2023/02/230221180110.htm   
      
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