Simulation of future impact of black carbon emissions from the Northern and Transpolar Sea routes on Arctic sea ice

Poltronieri, Anna; Bochow, Nils; Rypdal, Martin

doi:https://doi.org/10.5194/egusphere-2025-1134

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https://doi.org/10.5194/egusphere-2025-1134

Preprints

03 Apr 2025

| 03 Apr 2025

Status: this preprint is open for discussion and under review for The Cryosphere (TC).

Simulation of future impact of black carbon emissions from the Northern and Transpolar Sea routes on Arctic sea ice

Anna Poltronieri, Nils Bochow, and Martin Rypdal

Abstract. As sea ice decreases, navigation in the Arctic is becoming more feasible, and new routes are likely to emerge. However, the impact of these potential routes on sea ice remains uncertain. In this study, we compare the regional impacts of two major Arctic routes: the Northern Sea Route (NSR) and the Transpolar Sea Route (TSR). Using the Community Earth System Model (CESM2), we simulate black carbon (BC) emissions until 2050 along these routes and assess their effects on Arctic sea ice (ASI). We focus on regional changes in net shortwave (SW) radiation, sea ice extent, and surface temperature. While our study does not account for other pollutants that could counteract BC effects, our results reveal significant differences in ASI's response between routes. The TSR, in particular, exerts a stronger and more widespread influence on ASI than the NSR across all seasons, especially in increasing net SW radiation over the ice.

Received: 19 Mar 2025 – Discussion started: 03 Apr 2025

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Anna Poltronieri, Nils Bochow, and Martin Rypdal

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RC1: 'Comment on egusphere-2025-1134', Anonymous Referee #1, 11 Apr 2025 reply

The hypothesis proposed here is that black carbon (BC) emitted by ships in the Arctic will get into snow and reduce its albedo, enough to noticeably affect the absorbed SW radiation.
Before undertaking a research project to test a hypothesis, it is advisable first to make a quick calculation with pencil and paper to see whether the hypothesis is worth pursuing. The authors did not do this, so I will do it here:
(1) The BC emitted per month for the 2040s, from Figure 1c, will be 15 tons. From Figure 1a, it looks like the area affected by the TSR is 4x10⁶ km². So the monthly deposition of BC is 3750 ng m^-2.
(2) The snowfall per month over the Arctic Ocean is 1 g cm^-2 or 10⁴ g m^-2 (Webster et al., 2014).
(3) Combining those two numbers, the mixing ratio of BC in snow (due to shipping emissions) will be 0.4 ng/g. This is small compared to the typical BC mixing-ratio found in snow on the Arctic Ocean, 7 ng/g (Doherty et al., 2010). A mixing ratio of 0.4 ng/g is also too small to affect snow albedo (Dang et al., 2015).
The tiny radiative forcing resulting from this mixing ratio is surely the reason the authors were unable to offer explanations for their model’s behavior. The model results are likely just due to internal variability of the model’s climate. Here are some examples of unsatisfying inconclusive statements, with hedging like “suggests”, “might be”:
“No significant change in net SW under the NSF scenario, . . . However, increasing trends under the TSR scenario”. No explanation offered.
“Since no significant changes in cloud cover, snow cover, or melt ponds, this suggests that increased SW is due to decrease in albedo caused by BC”.
“The grid cells with low and high SIC show a decline in net SW”. This is odd: BC should cause an increase in net SW.
“The reason for the increase in net SW might be a drop in albedo.”
In Table A1, why the decrease in net SW in Greenland Sea and Baffin Bay?
In the eleven tables, there is little attempt to explain the positive and negative changes, often with conflicting results in neighboring regions.
References
Dang, C., R.E. Brandt, and S.G. Warren, 2015: Parameterizations for narrowband and broadband albedo of pure snow, and snow containing mineral dust and black carbon. J. Geophys. Res., 120, doi:10.1002/2014JD022646.
Doherty, S.J., S.G. Warren, T.C. Grenfell, A.D. Clarke, and R.E. Brandt, 2010: Light-absorbing impurities in Arctic snow. Atmos. Chem. Phys., 10, 11647-11680.
Webster, M.A., et al., 2014: Interdecadal changes in snow depth on Arctic sea ice. JGR Oceans, 119, 5395-5406, doi:10.1002/2014JC009985.

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Citation: https://doi.org/10.5194/egusphere-2025-1134-RC1

Anna Poltronieri, Nils Bochow, and Martin Rypdal

Data sets

CESM2 simulations for NSR and TSR Anna Poltronieri https://zenodo.org/records/13991609

Anna Poltronieri, Nils Bochow, and Martin Rypdal

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Short summary

As Arctic sea ice shrinks, new shipping routes become more accessible. This study compares the effects of two main Arctic pathways: the Northern and the Transpolar Sea routes. Using a high-complexity climate model, we simulate black carbon emissions from ships. When deposited on sea ice, black carbon increases solar absorption, enhancing melt. We analyze absorbed solar radiation, sea ice extent, and air temperature, finding that the Transpolar Sea Route has a greater effect on Arctic sea ice.


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