Reduced Black Carbon Deposition Weakens Arctic Snow Darkening and Snowmelt Acceleration during 2046–2050

Abstract. Air-pollution mitigation can reduce Arctic black carbon (BC) deposition and thereby slow Arctic warming by weakening snow darkening and associated radiative effects. Yet the regional land-surface benefits of future BC-deposition reductions across contrasting mitigation pathways remain poorly quantified. We use Polar-WRF coupled online with the SNICAR snow-albedo scheme to isolate the effects of spatially heterogeneous BC deposition associated with low-emission (SSP1-2.6), intermediate-emission (SSP2-4.5), and high-emission (SSP5-8.5) pathways during 2046–2050. All experiments share an SSP2-4.5 large-scale meteorological background and differ only in prescribed BC deposition; they therefore quantify the BC-deposition pathway rather than the full climate response to each SSP. Relative to simulations without BC in snow, Arctic-mean spring snow albedo decreases by 16.9 %, 18.1 %, and 19.3 % under SSP1-2.6, SSP2-4.5, and SSP5-8.5, respectively. BC deposition increases surface net radiation by 1.0–1.4 W m⁻², spring snowmelt by 4.1–6.1 mm d⁻¹, advances snow disappearance by 6.7–7.6 days, and increases Arctic land-mean near-surface air temperature by 0.09–0.12 °C. Compared with SSP5-8.5, the 39.6 % lower BC deposition under SSP1-2.6 produces 12.4 %, 28.6 %, and 32.8 % smaller BC-induced changes in snow albedo, net radiation, and snowmelt, respectively. Responses are regionally heterogeneous: Greenland shows the strongest albedo and snowmelt responses despite relatively low deposition, whereas the European Arctic and West Siberia show stronger radiative responses, where substantial snow darkening coincides with greater incoming solar radiation. These results provide a process-based, regional evaluation of the deposition-related Arctic climate benefits of mid-century mitigation pathways.