Relationships among Arctic warming, sea-ice loss, stability, lapse rate feedback, and Arctic amplification

The Arctic warms much faster than other places under increasing greenhouse gases, a phenomenon known as Arctic amplification (AA). Arctic positive lapse-rate feedback (LRF) and oceanic heating induced by sea-ice loss have been considered as major causes of Arctic warming and AA, and Arctic high atmospheric stability has been considered as a key factor for the occurrence of the bottom-heavy warming profile and thus positive LRF in the Arctic. Here we analyze model simulations with and without large AA and sea-ice loss and long-term changes in ERA5 reanalysis data to examine the relationships among Arctic sea-ice loss, stability, LRF, Arctic warming, and AA. Results show that the Arctic bottom-heavy warming profile and the resultant positive LRF are produced primarily by increased oceanic heating of the air due to sea-ice loss in Arctic winter, rather than high atmospheric stability. Without the oceanic heating induced by sea-ice loss, most Arctic climate feedbacks weaken greatly, and all other processes can only produce slightly enhanced surface warming and thus weak positive LRF under stable Arctic air. A non-convective Arctic environment allows the oceanic heating to warm near-surface air more than the upper levels, resulting in large positive LRF that roughly doubles the surface warming compared with the case without the LRF. We conclude that enhanced cold-season oceanic heating due to sea-ice loss is the primary cause of Arctic large positive LRF, which in turn allows the surface heating to produce more Arctic warming and large AA.