The importance of snow albedo for ice sheet evolution over the last glacial cycle

Abstract

Abstract. The surface energy and mass balance of ice sheets strongly depends on the amount of solar radiation absorbed at the surface, which is mainly controlled by the albedo of snow and ice. Here, using an Earth system model of intermediate complexity, we explore the role played by surface albedo for the simulation of glacial cycles. We show that the evolution of the Northern Hemisphere ice sheets over the last glacial cycle is very sensitive to the representation of snow albedo in the model. It is well known that the albedo of snow depends strongly on snow grain size and the content of lightabsorbing impurities. Excluding either the snow aging effect or the dust darkening effect on snow albedo leads to an excessive ice build-up during glacial times and consequently to a failure in simulating deglaciation. While the effect of snow grain growth on snow albedo is well constrained, the albedo reduction due to the presence of dust in snow is much more uncertain because the light-absorbing properties of dust vary widely as a function of dust mineral composition. We also show that assuming slightly different optical properties of dust leads to very different ice sheet and climate evolutions in the model. Conversely, ice sheet evolution is less sensitive to the choice of ice albedo in the model. We conclude that a proper representation of snow albedo is a fundamental prerequisite for a successful simulation of glacial cycles.

Robust uncertainty assessment of the spatio-temporal transferability of glacier mass and energy balance models

“…The turbulent fluxes are associated with the second largest uncertainty in this study, which is in agreement with other studies that found larger uncertainties in the radiative forcing (Willis et al, 2002). Turbulent fluxes are important for determining short-term variations of melt rates due to, for example, changes in the stability regimes (Lang, 1981).…”

Light-Absorbing Impurities in Snow: A Personal and Historical Account

“…The albedolowering effect of dust was suggested by Will Kellogg to cause a negative feedback on ice-sheet growth (Figure 8 of Kellogg, 1975), as discussed by Warren (1984a). Indeed, climate modeling of iceage cycles now finds this albedo-lowering effect of dust necessary for deglaciation (Willeit and Ganopolski, 2018). And on a shorter time-scale, within the present interglacial, the "Little Ice Age" in the Alps is hypothesized to have been terminated by deposition of BC from the 19th-century industrialization of Europe (Painter et al, 2013).…”

Hypersensitivity of glacial summer temperatures in Siberia

“…During glacial times, the atmospheric dust load and dust deposition were likely substantially larger, particularly at the southern margins of the Northern Hemisphere ice sheets and over Siberia (Harrison et al, 2001;Lambert et al, 2015;Mahowald et al, 1999Mahowald et al, , 2006. Modeling studies have shown that the buildup of ice over Siberia can be strongly impacted by the effect of dust on the surface albedo as an increase of dust deposition on the snowpack leads to a lowering of the snow albedo that in turn leads to higher melt rates (Krinner et al, 2006;Willeit and Ganopolski, 2018).…”