Lee Yu-Chi, Liu Wei, Fedorov Alexey V, Feldl Nicole, Taylor Patrick C
Department of Earth and Planetary Sciences, University of California Riverside, Riverside, CA 92521.
Department of Geology and Geophysics, Yale University, New Haven, CT 06511.
Proc Natl Acad Sci U S A. 2024 Sep 24;121(39):e2402322121. doi: 10.1073/pnas.2402322121. Epub 2024 Sep 16.
Enhanced warming of the Arctic region relative to the rest of the globe, known as Arctic amplification, is caused by a variety of diverse factors, many of which are influenced by the Atlantic meridional overturning circulation (AMOC). Here, we quantify the role of AMOC changes in Arctic amplification throughout the twenty-first century by comparing two suites of climate model simulations under the same climate change scenario but with two different AMOC states: one with a weakened AMOC and another with a steady AMOC. We find that a weakened AMOC can reduce annual mean Arctic warming by 2 °C by the end of the century. A primary contributor to this reduction in warming is surface albedo feedback, related to a smaller sea ice loss due to AMOC slowdown. Another major contributor is the changes in ocean heat uptake. The weakened AMOC and its associated anomalous ocean heat transport divergence lead to increased ocean heat uptake and surface cooling. These two factors are inextricably linked on seasonal timescales, and their relative importance for Arctic amplification can vary by season. The weakened AMOC can also abate Arctic warming via lapse rate feedback, creating marked cooling from the surface to lower-to-mid troposphere while resulting in relatively weaker cooling in the upper troposphere. Additionally, the weakened AMOC increases the low-level cloud fraction over the North Atlantic warming hole, causing significant cooling there via shortwave (sw) cloud feedback despite the overall effect of sw cloud feedback being a slight warming of the average temperature over the Arctic.
北极地区相对于全球其他地区的加速变暖，即北极放大效应，是由多种不同因素引起的，其中许多因素受大西洋经向翻转环流（AMOC）的影响。在此，我们通过比较在相同气候变化情景下但处于两种不同AMOC状态的两套气候模型模拟，来量化整个21世纪AMOC变化在北极放大效应中的作用：一种是AMOC减弱的情况，另一种是AMOC稳定的情况。我们发现，到本世纪末，AMOC减弱可使北极年平均变暖降低2摄氏度。变暖减少的一个主要促成因素是地表反照率反馈，这与AMOC减缓导致的海冰损失减少有关。另一个主要促成因素是海洋热吸收的变化。AMOC减弱及其相关的异常海洋热输送散度导致海洋热吸收增加和表面冷却。这两个因素在季节时间尺度上紧密相连，它们对北极放大效应的相对重要性可能因季节而异。AMOC减弱还可通过 lapse rate反馈减轻北极变暖，从地表到对流层中低层产生明显冷却，而对流层上层的冷却相对较弱。此外，AMOC减弱增加了北大西洋变暖空洞上空的低云量，尽管短波（sw）云反馈对北极平均温度的总体影响是轻微变暖，但通过短波（sw）云反馈在那里导致显著冷却。
