PNNL

Abstract

As global temperatures increase, sea ice loss will increasingly enable commercial shipping traffic to cross the Arctic Ocean, where the ships’ particulate emissions may have strong regional effects. Previous studies have used radiative transfer models to assess the climate impacts of this increased shipping, though such models do not represent the many dynamic feedbacks that make Arctic climate highly complex. We investigate impacts of shipping emissions on Arctic climate using a fully coupled Earth system model (CESM 1.2.2) and a suite of newly-developed projections of 21st-century trans-Arctic shipping emissions. Trans-Arctic shipping will reduce Arctic warming by 2099 by nearly 1°C, due to sulfate-driven liquid water cloud formation during the melt season. Cloud fraction, lifetime, and liquid water path exhibit significant positive trends, cooling the lower atmosphere and surface. Positive feedbacks from sea ice growth-induced albedo increases and decreased downwelling longwave radiation due to reduced water vapor content amplify the cooling relative to the shipping-free Arctic. Importantly, the spatial patterns of relative cooling are not isolated to shipping routes, suggesting regional rather than local scale impacts of increased shipping. Our findings thus point to the complexity in Arctic climate responses to increased shipping traffic, justifying further study and policy considerations as trade routes open.