| Summary: | Permafrost and seasonally frozen ground comprise a critically important component of the dynamic arctic terrestrial system, constituting a closely tied subsystem interacting with snow cover, vegetation, and the overlying atmosphere. This permafrost subsystem regulates the local exchange of energy, water, and materials (including carbon and nitrogen), and its influence extends beyond the arctic land to the hydrosphere and the extra-tropical climate. Furthermore, the long timescale of permafrost dynamics requires evaluation of the evolution and impacts of the subsystem on the glacial-interglacial time frame. While some recent numerical projections show rapid and widespread degradation of permafrost in response to climate change during this century, global climate system models with physically based snow and permafrost dynamics have not been fully tested, using new observationally-based evidence, for spatial and temporal variability of the subsystem under different climate conditions such as the Holocene optimum or the Last Glacial Maximum (LGM). Evaluation of the climate sensitivity to the permafrost will provide vital insight to future scenarios, especially in the Northern Hemisphere. The focus will be on three late Quaternary eras for which numerical simulations are widely performed by the collaborative efforts of the Paleoclimate Model Intercomparison Project (PMIP: i.e., the preindustrial present (0 ka, where ka = thousand years before present), mid-Holocene (6 ka), and the LGM (21ka). This project will focus on evaluating the structure and function of the permafrost subsystem under different climate conditions.
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