How important are future marine and shipping aerosol emissions in warming Arctic summer and autumn?

Abstract

Abstract. Future sea ice retreat in the Arctic in summer and autumn is expected to affect both natural and anthropogenic aerosol emissions: sea ice acts as a barrier between the ocean and the atmosphere, and reducing it increases dimethyl sulphide and sea salt emissions. A decrease in the area and thickness of sea ice could in addition lead to enhanced Arctic ship traffic, e.g. to shorten the paths of cargo ships. Changes in the emissions of aerosol particles can then influence cloud properties, precipitation, surface albedo, and radiation. Next to changes in aerosol particles, clouds will also be affected by increases in 5 Arctic temperatures and humidities. In this study, we quantified how future aerosol radiative forcing, aerosol-cloud interactions, and cloud radiative effects might change in the Arctic in late summer (July/August) and early autumn (September/October).Simulations were conducted for the years 2004 and 2050 with the global aerosol-climate model ECHAM6-HAM2. In 2050, simulations with and without additional ship emissions in the Arctic were carried out to quantify the impact of these emissions on the Arctic climate. 10We found that aerosol number concentrations in the Arctic will generally increase in the future due to enhanced emissions of sea salt as well as dimethyl sulphide. The increase in cloud condensation nuclei will enhance cloud droplet number concentrations over the Arctic Ocean. Furthermore, both liquid and total water content will increase since the specific humidity will be enhanced due to higher temperatures and the exposure of the ocean's surface.Changes in both aerosol radiative forcings and cloud radiative effects at the top of the atmosphere will not be dominated by 15 the aerosol particles and clouds themselves but by the decrease in surface albedo (and by the increase in surface temperature for the longwave cloud radiative effect). Due to the reduction in sea ice, the aerosol radiative forcing will become less positive and the cloud radiative effect more negative, i.e. the cooling component of both will gain importance in the future.We found that future Arctic ship emissions related to transport and oil/gas extraction (Peters et al., 2011, ACP) will not have a large impact on clouds and radiation: changes in aerosol concentrations only become significant when we increase 20 these ship emissions by a factor of ten. The net aerosol radiative forcing shows only small, non-significant changes. Enhanced black carbon deposition on snow leads to a significant but very small warming over the central Arctic Ocean in early autumn.Furthermore, the tenfold higher ship emissions increase the optical thickness of low clouds and thus induce a small Twomey effect (cooling) in late summer. This Twomey effect has a considerably larger influence on temperature than the direct effect of particles (both aerosol particles in the atmosphere and particles deposited on snow), but it is more uncertain because of the 25 1 Atmos. Chem. Phys. Discuss., https://doi

Infrared-absorbing carbonaceous tar can dominate light absorption by marine-engine exhaust

“…Whereas the Chakrabarty et al 16 data are not significantly different from ours, the tar brC observed by Alexander et al 15 appears to be more mature than that observed in our study, according to its lower AAEs of~2. Greater maturity is 11,12 ). The BC and tar brC AAEs and MAEs were retrieved from the data of Fig.…”

“…11 Fundamental differences in physical properties also impact the interpretation of fundamental LAC measurements and treatment in model simulations. 12 Insoluble LAC species include BC as well as the "tar ball" brC previously identified by electron microscopy in wildfire and biomass-burning samples, [13][14][15][16][17][18] which has fundamentally different properties to both BC and soluble brC. It is therefore essential to understand the chemical nature of LAC in HFO-PM in order to predict its environmental impacts and atmospheric mixing state, and to develop analytical techniques suitable for its quantification.…”

“…npj Climate and Atmospheric Science (2019)12 Published in partnership with CECCR at King Abdulaziz University…”

Processes Controlling the Composition and Abundance of Arctic Aerosol

“…Arctic regions are largely a marine, or coastal marine, environment beginning in late spring and extending into the autumn. Increases in PMA production are expected in the future from the increasingly exposed ocean surface as sea ice retreats (Browse et al, ; Gilgen et al, ; Struthers et al, ) and with the increased presence of first year ice that is thin and prone to fracturing (Maslanik et al, ; Overland & Wang, ; Stroeve et al, ). As discussed in section , sea salt concentrations peak in the winter–spring at ground stations, and areas of open water (i.e., leads, polynas) in ice‐covered regions are likely contributors to PMA during this time of year (e.g., Deshpande & Kamra, ; Kirpes et al, ; Leck et al, ; May et al, ; Nilsson et al, ; Scott & Levin, ; Weinbruch et al, ).…”

Climatic Responses to Future Trans‐Arctic Shipping

“…Using chemical transport and radiative forcing models, Dalsøren et al () found warming under two spatially explicit emission scenarios (Peters et al, ) between 2004 and 2030, while Fuglestvedt et al () used a simple 2‐box climate model to demonstrate enhanced Arctic warming from short‐lived shipping pollutants until 2160. In contrast, Gilgen et al () found net cooling by 2050 using a global aerosol‐climate model, driven by enhanced cloud droplet number and optical thickness of clouds over the Arctic Ocean. Although highly relevant to environmental impacts of future shipping, the methods and emission projections used previously are not capable of evaluating dynamic feedbacks in the physical climate and human activities.…”