Field Guide to: Permafrost Research
- Carbon Reservoir
- Hydrologic Cycle
- Modeling (CCSM)
Image provided by the National Snow and Ice Data Center. Click to visit NSIDC's permafrost mapping.
Current Permafrost Map (left)
Covering an area slightly smaller than South America, permafrost extends across more than 24% of the Northern Hemisphere. Given current climate trends, scientists predict greatly reduced permafrost extent by the end of the 21st century. This may have serious repercussions on both regional and global climate.
Defined as ground perennially frozen for more than two years, permafrost exists at high latitudes and, to a lesser degree, high elevations. Scientists have classified permafrost into three categories: continuous (uninterrupted permafrost), discontinuous (permafrost broken up by patches of thawed ground), and sporadic (small permafrost oases surrounded by seasonally thawed ground). Permafrost depth ranges from several centimeters to hundreds of meters.
Click to enlarge. Estimate of the observed global distribution of soil organic matter (Global Soil Data Task, 2000).
Click to enlarge. Permafrost features on the Norwegian island of Kvadehuksletta, 1999. (Photo by Ólafur Ingólfsson, professor of glacial and quaternary geology, University of Iceland. web: http://www.hi.is/~oi/index.htm).
Permafrost as Carbon Reservoir
"There's a lot of carbon stored in the soil," says NCAR scientist David Lawrence. "If the permafrost does thaw, as our model predicts, it could have a major influence on climate." Today, permafrost acts as a carbon reservoir – and a big one at that. Permafrost effectively traps organic-rich soil and vegetation in a frozen substrate, which prevents decomposition. However, once thawed, this organic matter has the potential to release substantial amounts of carbon into the atmosphere.
Click to enlarge. Illustration of the hydrologic cycle.
Click to enlarge. This sinkhole near Fairbanks, Alaska, formed due to the melting of a large ice pocket within permafrost. (Photo courtesy Vladimir Romanovsky, Geophysical Institute, University of Alaska Fairbanks.)
The Hydrologic Cycle
In addition to its atmospheric impacts, thawing permafrost affects the hydrologic cycle, increasing groundwater discharge to the Arctic Ocean and influencing regional lake abundance. Receding permafrost will also have a bearing on vegetation extent and type in the Arctic and subarctic. As temperatures warm and permafrost recedes, shrubs and other plants that typically thrive in warmer, more southerly regions will grow more readily throughout the tundra. In addition, degrading permafrost often results in ground subsidence, which impacts the stability of structures such as buildings and oil and gas pipelines.
Click to enlarge. Arctic warming feedback diagram.
Click to enlarge. Although there is considerable uncertainty, regions containing permafrost within the top 11 feet (3.35 meters) of soil could decrease by as much as 90% across the Arctic over the next century, based on simulations by the NCAR Community Climate System Model. Shown are areas with near-surface permafrost in the CCSM simulations for 1980-1999 (light blue) and 2080-2099 (dark blue). The latter projection is based on the Intergovernmental Panel on Climate Change's A1B emissions scenario, often called the "business as usual" scenario.
The CCSM Model's Use in Predicting Permafrost Decline
To study these and other impacts, NCAR’s David Lawrence uses the Community Climate System Model (CCSM) to look at present-day and future high-latitude permafrost distribution.
Climate affects – and is affected by – the physical, chemical, and biological interactions of these northerly ecosystems. Using CCSM, NCAR and its collaborators are gaining a better understanding of the regional cycling of energy, water, chemical elements, and trace gases. This helps them predict both future permafrost extent and the impacts of any changes.
Click to enlarge. Results of a 2005 study by David Lawrence. Ensemble mean permafrost area and active layer thickness as simulated in CCSM3 at the end of the (a) 20th and (b) 21st centuries. (c) Observational estimates of permafrost (continuous, discontinuous, sporadic, and isolated). (d) Time series of simulated global permafrost area (excluding glacial Greenland and Antarctica). The gray shaded area represents the ensemble spread.
Click to enlarge.Thaw lakes in the North of Quebec, Canada (From Isabelle Laurion, INRS-ETE, QC. Website: http://www.cen.ulaval.ca/merge/index.php?url=11112).
Preliminary model results, which match well with observational data, show near-surface permafrost extent reduced dramatically by 2100. With plans to update the model to include an organic soil component, and greater soil column depths, scientists expect to enhance the Community Climate System Model (CCSM), and reevaluate predictions in the near future.