Abstract
Abstract. Here, global-scale frozen ground distribution from the Last Glacial Maximum (LGM) has been reconstructed using multi-model ensembles of global climate models, and then compared with evidence-based knowledge and earlier numerical results. Modeled soil temperatures, taken from Paleoclimate Modelling Intercomparison Project phase III (PMIP3) simulations, were used to diagnose the subsurface thermal regime and determine underlying frozen ground types for the present day (pre-industrial; 0 kya) and the LGM (21 kya). This direct method was then compared to an earlier indirect method, which categorizes underlying frozen ground type from surface air temperature, applying to both the PMIP2 (phase II) and PMIP3 products. Both direct and indirect diagnoses for 0 kya showed strong agreement with the present-day observation-based map. The soil temperature ensemble showed a higher diversity around the border between permafrost and seasonally frozen ground among the models, partly due to varying subsurface processes, implementation, and settings. The area of continuous permafrost estimated by the PMIP3 multi-model analysis through the direct (indirect) method was 26.0 (17.7) million km2 for LGM, in contrast to 15.1 (11.2) million km2 for the pre-industrial control, whereas seasonally frozen ground decreased from 34.5 (26.6) million km2 to 18.1 (16.0) million km2. These changes in area resulted mainly from a cooler climate at LGM, but from other factors as well, such as the presence of huge land ice sheets and the consequent expansion of total land area due to sea-level change. LGM permafrost boundaries modeled by the PMIP3 ensemble – improved over those of the PMIP2 due to higher spatial resolutions and improved climatology – also compared better to previous knowledge derived from geomorphological and geocryological evidence. Combinatorial applications of coupled climate models and detailed stand-alone physical-ecological models for the cold-region terrestrial, paleo-, and modern climates will advance our understanding of the functionality and variability of the frozen ground subsystem in the global eco-climate system.
Highlights
Frozen ground constitutes a critical environmental subsystem of the Arctic eco-climate, closely linked with snow and vegetation (Nelson, 2003; Saito et al, 2013a)
Saito et al.: Last Glacial Maximum (LGM) permafrost distribution variations, and stability under a different and/or changing climate is a crucial element in Earth science research, as well as in social sciences and policy making (UNEP, 2012)
This paper provides a descriptive analysis of the multi-model PMIP3 ensemble, with respect to distribution of modeled surface and subsurface thermal states, and the geographical extent of reconstructed near-surface frozen ground
Summary
Frozen ground (i.e., permafrost and seasonally frozen ground) constitutes a critical environmental subsystem of the Arctic eco-climate, closely linked with snow and vegetation (Nelson, 2003; Saito et al, 2013a). Threshold values are different for different application areas, periods, and types of permafrost (for example, Washburn (1980) cites −2 ◦C as the upward limit for permafrost, and uses the range of −5 ◦C to −10 ◦C for the presence of continuous permafrost for different regions) This is partly a manifestation of subsurface thermal regime not being a function of air temperature alone, but it depends on other factors such as snow cover, vegetation, soils, and micro-topography (French, 2007; Saito et al, 2013a). Progress in modeling frozen ground characteristics after PMIP2 simulations is assessed through comparisons with the evidencebased knowledge and maps currently available
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