Future increase in Arctic moisture transport dominated by midlatitude CO2 forcing

<p>Northward transport of moisture is a key driver of Arctic warming and is projected to increase in the future. However, the importance of local versus remote forcing, and the mechanisms through which they impact the Arctic, are unclear. Here, we determine the causes of increased Arctic moisture transport using climate model simulations in which idealised CO2 forcing is prescribed in distinct latitudinal regions. The sum of the regional responses reproduce the response to global forcing and resembles the future change seen in state-of-the-art climate model projections. Midlatitude forcing dominates future changes in Arctic moisture transport, while tropical and polar forcing play a secondary role. Increases in zonal-mean Arctic moisture transport result mostly from changes in transient eddy transport and scale with increased water vapour. Similar increases are found in an analogous set of simulations without the presence of land and orography, suggesting climatological zonal asymmetries, such as stationary eddies and gradients of sea-surface temperature, do not set the first-order zonal-mean response. In contrast, zonal changes in Arctic moisture transport are dominated by changes in stationary eddy transport, where both increased water vapour and meridional wind changes are important. Thus, the future increase in Arctic moisture transport depends primarily on dynamic and thermodynamic processes forced in midlatitudes.</p>