In recent decades, the Arctic has witnessed significant environmental change ranging from decreases in sea ice extent, increases in shrub cover and melting glaciers. Temperatures over Arctic land are rising at roughly twice the rate of the rest of the world. Permafrost, which is defined as soil or rock that remains below 0oC for two or more years, is an archetypal component of the Arctic climate system. In harmony with other aspects of change, permafrost temperatures are rising and there have been reports of significant permafrost degradation in some locations.
Results from the NCAR Community Climate System Model (CCSM3) indicate that degradation of permafrost will continue and may accelerate during the 21st century. The CCSM3 is a mathematical model of the global climate system that includes components representing the atmosphere, ocean, land, and sea-ice. The land model component is limited to simulating the top 3.5m of the ground, though this is the ecologically and hydrologically important portion; deeper permafrost is not as vulnerable at the century timescale. The present-day global distribution of near-surface permafrost in the CCSM3 compares well with observed estimates of permafrost distribution both in terms of geographical extent and total area (~10.5 million km2). Projections of the fate of near-surface permafrost are assessed through simulations of the 21st century climate under various greenhouse gas emission scenarios provided by the Intergovernmental Panel on Climate Change (IPCC). Under the “business as usual” emission scenario (A1B), the area containing permafrost in the near-surface layer declines by ~80% by 2100. Under a lower emission scenario (B1), the degradation of permafrost is less severe (~60%) but still substantial.
There are considerable uncertainties in both the magnitude and the timing of the projected near-surface permafrost degradation due to deficiencies in the model that include biases in the simulated climate, an imperfect land model, and feedbacks that are not fully-represented in the model. Nonetheless, this result in conjunction with the observed permafrost warming across the Arctic suggests that large-scale changes in permafrost are likely. The potential climate feedbacks associated with a degradation of near-surface permafrost are diverse. Changes to Arctic vegetation, hydrology, and the carbon cycle are expected in the form of expanding shrub cover and northward forest migration, enhanced runoff to the Arctic Ocean as well as expanding and retreating lakes and wetlands, and the release of large quantities of soil carbon, currently frozen in permafrost soil, into the atmosphere. These feedbacks could contribute to an acceleration of global climate change.
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About the speaker:
Dr. David Lawrence is a research scientist at the National Center for Atmospheric Research (NCAR) in Boulder, Colorado. His research interests are centered around land-atmosphere interactions and improving our understanding of the role of land surface processes in the Earth’s climate system and their influence on climate change. He is involved in the assessment and development of NCAR’s Community Climate System Model (CCSM) and is co-chair of the CCSM Land Model Working Group. Previously he completed a post-doc at the Department of Meteorology at the University of Reading in the United Kingdom. He received his Ph.D. in 1999 from the Department of Atmospheric and Oceanic Science at the University of Colorado.
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