Arctic climate response to forcing from light-absorbing particles in snow and sea ice in CESM

Abstract

Abstract. The presence of light-absorbing aerosol particles deposited on arctic snow and sea ice influences the surface albedo, causing greater shortwave absorption, warming, and loss of snow and sea ice, lowering the albedo further. The Community Earth System Model version 1 (CESM1) now includes the radiative effects of light-absorbing particles in snow on land and sea ice and in sea ice itself. We investigate the model response to the deposition of black carbon and dust to both snow and sea ice. For these purposes we employ a slab ocean version of CESM1, using the Community Atmosphere Model version 4 (CAM4), run to equilibrium for year 2000 levels of CO 2 and fixed aerosol deposition. We construct experiments with and without aerosol deposition, with dust or black carbon deposition alone, and with varying quantities of black carbon and dust to approximate year 1850 and 2000 deposition fluxes. The year 2000 deposition fluxes of both dust and black carbon cause 1-2 • C of surface warming over large areas of the Arctic Ocean and subArctic seas in autumn and winter and in patches of Northern land in every season. Atmospheric circulation changes are a key component of the surface-warming pattern. Arctic sea ice thins by on average about 30 cm. Simulations with year 1850 aerosol deposition are not substantially different from those with year 2000 deposition, given constant levels of CO 2 . The climatic impact of particulate impurities deposited over land exceeds that of particles deposited over sea ice. Even the surface warming over the sea ice and sea ice thinning depends more upon light-absorbing particles deposited over land. For CO 2 doubled relative to year 2000 levels, the climate impact of particulate impurities in snow and sea ice is substantially lower than for the year 2000 equilibrium simulation.

Advances in understanding and parameterization of small-scale physical processes in the marine Arctic climate system: a review

“…The Flanner et al estimation of global annual mean BC/snow surface radiative forcings (0.054 and 0.049 Wm −2 during strong (1998) and weak (2001) boreal fire years) was in line with the IPCC AR4 estimation (IPCC, 2007) and was later confirmed by other studies Goldenson et al, 2012). Over large areas of the Arctic Ocean and sub-Arctic seas, the autumn and winter near-surface warming resulting from this radiative forcing is 1-2 • C (Goldenson et al, 2012).…”

“…Over large areas of the Arctic Ocean and sub-Arctic seas, the autumn and winter near-surface warming resulting from this radiative forcing is 1-2 • C (Goldenson et al, 2012). Through 20th century equilibrium climate experiments, Koch et al (2009) obtained a 0.5 • C mean Arctic surface warming due to the BC/snow albedo effect.…”

“…Through 20th century equilibrium climate experiments, Koch et al (2009) obtained a 0.5 • C mean Arctic surface warming due to the BC/snow albedo effect. In equilibrium climate experiments, the effect of present-day aerosol deposition on sea ice thickness was estimated to be a thinning of about 30 cm (averaged over the year) compared to a scenario without aerosol deposition (Goldenson et al, 2012;Holland et al, 2012). Nevertheless, since the BC content in Arctic snow has decreased since the 1980s, it is improbable that the present aerosol load has contributed to the recently observed rapid decline of Arctic sea ice.…”

“…Further, melt ponds enhance the SAF because of enhanced melt pond coverage in a warmer climate, while aerosol deposition on ice (when kept constant) reduces the SAF because of enhanced melt-out of aerosols in a warmer climate . Thus, the impact of particulate impurities on snow and sea ice is expected to decrease in a doubling CO 2 scenario Goldenson et al, 2012). Finally, the SAF can be enhanced by mechanical processes: a thinner, less concentrated sea ice cover is weaker (Gimbert et al, 2012b), which results in increasing fracturing and lead opening.…”

“…Among the prognostic schemes, one of the most sophisticated is the model introduced by Dickinson et al (1993), which accounts for the albedo dependence on spectral bands and direction of the illumination. It has been implemented in many climate models Goosse et al, 2009), and it has also been coupled to an explicit treatment of melt pond albedo .…”