|Title||Polar amplification dominated by local forcing and feedbacks|
|Publication Type||Journal Article|
|Year of Publication||2018|
|Authors||Stuecker M.F, Bitz C.M, Armour K.C, Proistosescu C., Kang S.M, Xie SP, Kim D., McGregor S., Zhang W.J, Zhao S., Cai W.J, Dong Y., Jin F.F|
|Journal||Nature Climate Change|
|Type of Article||Article|
|Keywords||Climate sensitivity; Environmental Sciences & Ecology; Meteorology & Atmospheric Sciences; model; pattern; remote impacts; sea-ice|
The surface temperature response to greenhouse gas forcing displays a characteristic pattern of polar-amplified warming(1-5), particularly in the Northern Hemisphere. However, the causes of this polar amplification are still debated. Some studies highlight the importance of surface-albedo feedback(6-8), while others find larger contributions from longwave feedbacks(4,9,10), with changes in atmospheric and oceanic heat transport also thought to play a role(11-16). Here, we determine the causes of polar amplification using climate model simulations in which CO2 forcing is prescribed in distinct geographical regions, with the linear sum of climate responses to regional forcings replicating the response to global forcing. The degree of polar amplification depends strongly on the location of CO2 forcing. In particular, polar amplification is found to be dominated by forcing in the polar regions, specifically through positive local lapse-rate feedback, with ice-albedo and Planck feedbacks playing subsidiary roles. Extra-polar forcing is further shown to be conducive to polar warming, but given that it induces a largely uniform warming pattern through enhanced poleward heat transport, it contributes little to polar amplification. Therefore, understanding polar amplification requires primarily a better insight into local forcing and feedbacks rather than extra-polar processes.
|Short Title||Nat. Clim. Chang.|
The question of which processes contribute most to polar amplification is still strongly debated. Here, we have found that the response of the climate system to different regional forcing is remarkably linear, both in transient coupled atmosphere–ocean simulations and equilibrium slab ocean simulations. These results suggest that while remote forcing from outside the polar regions can contribute to polar warming, it makes a negligible contribution to polar amplification.