Simulated Historical (1901–2010) Changes in the Permafrost Extent and Active Layer Thickness in the Northern Hemisphere

Abstract

A growing body of simulation research has considered the dynamics of permafrost, which has an important role in the climate system of a warming world. Previous studies have concentrated on the future degradation of permafrost based on global climate models (GCMs) or data from GCMs. An accurate estimation of historical changes in permafrost is required to understand the relations between changes in permafrost and the Earth's climate and to validate the results from GCMs. Using the Community Land Model 4.5 driven by the Climate Research Unit ‐National Centers for Environmental Prediction (CRUNCEP) atmospheric data set and observations of changes in soil temperature and active layer thickness and present‐day areal extent of permafrost, this study investigated the changes in permafrost in the Northern Hemisphere from 1901 to 2010. The results showed that the model can reproduce the interannual variations in the observed soil temperature and active layer thickness. The simulated area of present‐day permafrost fits well with observations, with a bias of 2.02 × 106 km2. The area of permafrost decreased by 0.06 (0.62) × 106 km2 decade−1 from 1901 to 2009 (1979 to 2009). A clear decrease in the area of permafrost was found in response to increases in air temperatures during the period from about the 1930s to the 1940s, indicating that permafrost is sensitive to even a temporary increase in temperature. From a regional perspective, high‐elevation permafrost decreases at a faster rate than high‐latitude permafrost; permafrost in China shows the fastest rate of decrease, followed by Alaska, Russia, and Canada. Discrepancies in the rate of decrease in the extent of permafrost among different regions were mostly linked to the sensitivity of permafrost in the regions to increases in air temperatures rather than to the amplitude of the increase in air temperatures. An increase in the active layer thickness of 0.009 (0.071) m decade−1 was shown during the period of 1901–2009 (1979–2009). These results are useful in understanding the response of permafrost to a historical warming climate and for validating the results from GCMs.

Simulation of Changes in the Near‐Surface Soil Freeze/Thaw Cycle Using CLM4.5 With Four Atmospheric Forcing Data Sets

“…The data cover a period of 1901–2010 at a spatial (temporal) resolution of 0.5° × 0.5° (six‐hourly). The CRUNCEP data have been employed to force CLM for studies on various topics such as vegetation growth, evapotranspiration, permafrost dynamics (Guo & Wang, ; Mao et al, ; Shi et al, ).…”

The ERA5-Land soil temperature bias in permafrost regions

“…First, the results from statistical evaluations of coarse-scale products such as ERA5L depend significantly on the local selection of observation sites. This issue is known as the spatial effect which is when the lack of spatially distributed measurements consistent with the size of model grid cells (i.e., 0.1 • in ERA5L) is a potential source of error for model evaluation (Gupta et al, 2006;Gubler et al, 2011). Second, ERA5L ground temperatures can only represent at best a small fraction of the area within each individual grid cell.…”

Microtopography Controls of Carbon and Related Elements Distribution in the West Siberian Frozen Bogs

“…The second scenario assumes no change in micro-relief distribution but a northward retreat of the permafrost boundary and an increase in the ALT [100,101]. The ongoing changes and an increase in the active layer of wetlands [102] within the permafrost zone will lead to a change in the dynamics of the DOC and thus, the flows of associated elements [14,20,103]. Combining both scenarios, one can expect (1) fast migration of the permafrost boundary via increase of the ALT without changes in the microtope and (2) after several hundred years (following formation of a new peat layer of at least 20 cm thick), a replacement of mounds by hollows/fens.…”