The contribution of snow condition trends to future ground climate

Abstract

Global climate models predict that terrestrial northern high-latitude snow conditions will change substantially over the twenty-first century. Results from a Community Climate System Model simulation of twentieth and twenty-first (SRES A1B scenario) century climate show increased winter snowfall (?10-40%), altered maximum snow depth (-5 ± 6 cm), and a shortened snow-season (-14 ± 7 days in spring, ?20 ± 9 days in autumn). By conducting a series of prescribed snow experiments with the Community Land Model, we isolate how trends in snowfall, snow depth, and snow-season length affect soil temperature trends. Increasing snowfall, by countering the snowpackshallowing influence of warmer winters and shorter snow seasons, is effectively a soil warming agent, accounting for 10-30% of total soil warming at 1 m depth and *16% of the simulated twenty-first century decline in near-surface permafrost extent. A shortening snow season enhances soil warming due to increased solar absorption whereas a shallowing snowpack mitigates soil warming due to weaker winter insulation from cold atmospheric air. Snowpack deepening has comparatively less impact due to saturation of snow insulative capacity at deeper snow depths. Snow depth and snow-season length trends tend to be positively related, but their effects on soil temperature are opposing. Consequently, on the century timescale the net change in snow state can either amplify or mitigate soil warming.Snow state changes explain less than 25% of total soil temperature change by 2100. However, for the latter half of twentieth century, snow state variations account for as much as 50-100% of total soil temperature variations.

Soil temperature response to 21st century global warming: the role of and some implications for peat carbon in thawing permafrost soils in North America

“…The timing and magnitude of snowfall, the resulting snow depth, and the length of the snow season (the number of days with a significant snow pack on the ground) are some of the most important factors influencing the response of soil temperature to variations in air temperature (Stieglitz et al, 2003;Zhang et al, 2008a;Jorgenson et al, 2010;Lawrence and Slater, 2010) and therefore ultimately impact biogeochemical cycling rates in the soil (Schimel et al, 2004). Lawrence and Slater (2010) estimate that 50-100 % of the soil temperature changes by the end of the last century could be caused by variations in the snow state.…”

“…Lawrence and Slater (2010) estimate that 50-100 % of the soil temperature changes by the end of the last century could be caused by variations in the snow state.…”

“…A delayed offset of the snow season (earlier melt) increases the heat flux into the soil whereas a delay of the snow season onset can lead to both warming and cooling of the ground depending on the temporal patterns of air temperature and snowfall (Lawrence and Slater, 2010). If the delay is due to warmer air temperature and a delayed transition to below-freezing air temperatures, the result is a warming effect.…”

“…The response of soil temperatures to changes in air temperature strongly depends on the temporal distribution, depth, and density of the snowpack during the winter (Lawrence and Slater, 2010). The snowpack generally insulates the soil from the cold air and changes in the snowpack can therefore lead to more soil cooling (if the snowpack decreases) or warmer winter soil temperatures and permafrost degradation with a deeper snowpack (Christensen et al, 2004;Payette et al, 2004;Stieglitz et al, 2003).…”

An analysis of present and future seasonal Northern Hemisphere land snow cover simulated by CMIP5 coupled climate models

“…(ii) Hall and Qu (2006) and Fletcher et al (2012) have shown this feedback to be correctly represented only in a minority of the CMIP3 (Coupled Model Intercomparison Project -Phase 3: http://www-pcmdi.llnl.gov/ ipcc/about ipcc.php) models. Due to its low heat conductivity, snow also effectively insulates the underlying soil, with important effects on deep soil temperatures and permafrost extent (Zhang, 2005;Lawrence and Slater, 2010;Gouttevin et al, 2012).…”