The greater role of Southern Ocean warming compared to Arctic Ocean warming in shifting future tropical rainfall patterns

The recent rapid decline in Antarctic sea ice highlights the need to
understand whether rising Southern Ocean temperatures have an influence on
global climate. While Arctic warming has been extensively studied, the
importance of Southern Ocean warming is emerging only now.
 Multi-model simulations show that over 1.5°C of Southern Ocean
surface warming can offset the projected northward shift in tropical
zonal-mean precipitation by the mid-21st century, driven by stronger
northern high-latitude warming under rising greenhouse gas concentrations.
SST nudging experiments suggest that a 1.0°C warming in the Southern Ocean
could impact tropical precipitation as significantly as a 1.5°C warming in
the Arctic. Regionally, Southern Ocean warming increases rainfall in
northeastern Brazil while heightening drought risks in the Sahel. These
effects are comparable to, or slightly more pronounced than, those caused
by a weakening Atlantic meridional overturning circulation and the
associated development of the North Atlantic warming hole. Thus, Southern
Ocean warming may play a more crucial role than Arctic warming in shaping
tropical climate patterns in the coming decades.

近期南极海冰的快速消退，凸显了探究南大洋升温是否会对全球气候产生影响的必要性。尽管北极变暖已得到广泛研究，但南大洋升温的重要性直至今日才逐渐受到学界关注。多模式模拟结果显示，在温室气体浓度持续上升的背景下，受北半球高纬度地区更强升温驱动，当南大洋表层升温超过1.5℃时，可抵消21世纪中叶热带纬向平均降水预计出现的北移趋势。海表温度松弛（SST nudging）试验表明，南大洋升温1.0℃对热带降水的影响程度，可与北极升温1.5℃的影响相当。从区域尺度来看，南大洋升温会增加巴西东北部的降雨量，同时加剧萨赫勒地区的干旱风险。上述影响与大西洋经向翻转环流（Atlantic meridional overturning circulation）减弱以及与之相伴的北大西洋暖缺失区（North Atlantic warming hole）形成所引发的影响相当，甚至略更显著。因此，在未来数十年间，南大洋升温在塑造热带气候格局方面，或许比北极升温发挥更为关键的作用。