Observed Statistical Connections Overestimate the Causal Effects of Arctic Sea Ice Changes on Midlatitude Winter Climate
Observed Statistical Connections Overestimate the Causal Effects of Arctic Sea Ice Changes on Midlatitude Winter Climate
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DOI：
10.1175/jcli-d-20-0293.1
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发表时间：
2021-04-01
影响因子：
4.9
通讯作者：
Screen, James A.
中科院分区：
文献类型：
--
作者：
Blackport, Russell;Screen, James A.
解开北极海冰变化对中纬度冬季气候变率的贡献仍然具有挑战性，因为中纬度地区的内部气候变率很大，难以区分因果关系，方法差异以及模型是否充分模拟北极海冰和中纬度气候之间的联系的不确定性。我们使用回归分析来量化北极海冰和中纬度冬季气候之间的联系，在观测和大型初始条件合奏的多个气候模型，在耦合配置和所谓的大气模型相互比较项目（AMIP）配置，其中观测到的海冰和/或海面温度是规定的。耦合模型捕捉冬季巴伦支-卡拉海冰和欧亚表面温度之间的年际变化，冬季楚科奇-白令海冰和北美表面温度之间的联系。耦合模型还捕捉到了11月至12月巴伦茨-卡拉海冰减少、冬季平流层极涡减弱以及冬末北大西洋涛动向负相转变之间的延迟联系，尽管这种向下影响比观察到的要弱。连接的强度和符号在35年长的合奏成员之间有很大的差异，这突出了大型合奏将强大的连接与内部变异分开的必要性。在AMIP实验中，所有上述联系要么不存在，要么明显较弱，只观察到海冰的变化。我们的结论是，海冰的变化对中纬度冬季气候的因果影响比统计协会所建议的要弱得多，在观测和耦合模型中很明显，因为大气环流变化对海冰的影响夸大了统计数据。
Disentangling the contribution of changing Arctic sea ice to midlatitude winter climate variability remains challenging because of the large internal climate variability in midlatitudes, difficulties separating cause from effect, methodological differences, and uncertainty around whether models adequately simulate connections between Arctic sea ice and midlatitude climate. We use regression analysis to quantify the links between Arctic sea ice and midlatitude winter climate in observations and large initial-condition ensembles of multiple climate models, in both coupled configurations and so-called Atmospheric Model Intercomparison Project (AMIP) configurations, where observed sea ice and/or sea surface temperatures are prescribed. The coupled models capture the observed links in interannual variability between winter Barents-Kara sea ice and Eurasian surface temperature, and between winter Chukchi-Bering sea ice and North American surface temperature. The coupled models also capture the delayed connection between reduced November-December Barents-Kara sea ice, a weakened winter stratospheric polar vortex, and a shift toward the negative phase of the North Atlantic Oscillation in late winter, although this downward impact is weaker than observed. The strength and sign of the connections both vary considerably between individual 35-yr-long ensemble members, highlighting the need for large ensembles to separate robust connections from internal variability. All the aforementioned links are either absent or are substantially weaker in the AMIP experiments prescribed with only observed sea ice variability. We conclude that the causal effects of sea ice variability on midlatitude winter climate are much weaker than suggested by statistical associations, evident in observations and coupled models, because the statistics are inflated by the effects of atmospheric circulation variability on sea ice.