Arctic Climate Feedback Response to Local Sea-Ice Concentration and Remote Sea Surface Temperature Changes in PAMIP Simulations

Abstract

Local and remote processes have been suggested to drive Arctic amplification (AA) – the enhanced warming of the Arctic region relative to other areas under increased greenhouse gases. We use Polar Amplification Model Intercomparison Project (PAMIP) simulations with changes in Arctic sea-ice with fixed global sea surface temperature (SST), or changes in global SST with fixed Arctic sea-ice to untangle the climate response to Arctic sea-ice loss or SST-induced warming, respectively. In response to Arctic sea-ice loss, the surface albedo feedback activates in summer mainly to increase oceanic heat uptake, leading to weak summertime warming. During winter, Arctic sea-ice loss greatly enhances oceanic heat release, which produces Arctic bottom-heavy warming and triggers positive lapse rate and cloud feedbacks, leading to large AA. In contrast, enhanced atmospheric energy convergence into the Arctic becomes the dominant contributor to relatively small AA under global SST-induced warming. Water vapor feedback contributes to Arctic warming but opposes AA due to larger tropical than Arctic moistening under SST-induced warming with fixed Arctic sea-ice. We also find top-heavy to uniform (bottom-heavy) Arctic warming and moistening in the Arctic mid-upper (lower) troposphere in the SST (Arctic sea-ice) perturbation runs, producing a negative-neutral (positive) Arctic lapse rate feedback, respectively. Lastly, we show that the responses to global SST or polar SIC perturbations are linearly separable. Our results suggest that large AA is caused primarily by sea-ice loss and resultant local changes in surface fluxes, while increased poleward energy transport can only produce weak AA under fixed sea ice.