Elucidating the Role of Anthropogenic Aerosols In the Arctic Sea Ice Variations

Observations show that the Arctic sea ice cover has been shrinking at an 35 unprecedented rate since the 1970s. Even though the accumulation of greenhouse gases in the 36 atmosphere has been closely linked with the loss of the Arctic sea ice, the role of atmospheric 37 aerosols in the past and future Arctic climate change remains elusive. Using a state-of-the-art 38 fully coupled climate model, we show that aerosol perturbations impose significant influence on 39 the pace of sea ice melt, along with modulations from the ocean circulation and atmospheric 40 feedbacks. Because of the contrasting evolutions of particulate pollution in the developed and 41 developing countries since the 1970s, the opposite aerosol forcings from different mid-latitude 42 regions are nearly canceled out in the Arctic during the boreal summer, resulting in a muted 43 aerosol effect on the recent sea ice changes. Consequently the greenhouse forcing alone can 44 largely explain the observed Arctic sea ice loss till present. In the next few decades, the projected 45 alleviation of particulate pollution in the Northern Hemisphere can contribute up to 20% of the 46 total Arctic sea ice loss and 0.7 °C surface warming over the Arctic. Our model simulations 47 further show that aerosol microphysical effects on the Arctic clouds are the major component in 48 the total aerosol forcing. Aerosol variations and associated forcing within the Arctic, either due 49 to changes in local emissions or long-range transports, play a more crucial role than aerosol 50 radiative forcings over the lower latitude regions in determining the sea ice changes and the 51 Arctic climate change.