The Role of Atmospheric Feedbacks in Abrupt Winter Arctic Sea Ice Loss in Future Warming Scenarios
The Role of Atmospheric Feedbacks in Abrupt Winter Arctic Sea Ice Loss in Future Warming Scenarios
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DOI：
10.1175/jcli-d-20-0558.1
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发表时间：
2021-04
影响因子：
4.9
通讯作者：
Camille Hankel;E. Tziperman
中科院分区：
文献类型：
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作者：
Camille Hankel;E. Tziperman
在高排放扩展RCP8.5情景下，在耦合模式相互比较项目（CMIP 5）第5阶段运行的全球气候模式（GCM）中，对冬季北极海冰损失进行了不同程度的模拟。以前的研究提出了各种机制来解释模拟的冬季海冰突然损失，如冬季对流云反馈的存在或冰点作为自然阈值的作用，但没有一个试图解释整个GCM的冬季海冰损失的不稳定性的变化。在这里，我们提出了一个年复一年的本地正反馈周期，在冬季开始时温暖，开放的海洋允许低层大气的湿润和变暖，这反过来又增加了地面向下的晴空长波辐射，并抑制海洋冻结。这种情况导致冬季海冰增长延迟和减少，并允许在春季从较低的表面吸收短波。最后，海洋在整个夏季和秋季储存了这些额外的热量，创造了更温暖的海洋条件，导致海冰进一步减少。我们表明，这种反馈的强度，测量不同的表面热通量的部分温度的贡献，强烈相关的冬季海冰损失跨模型的快速性。因此，我们认为，这种反馈机制可以解释冬季海冰损失的不稳定性的模型间传播。在反馈机制很强的模型中，这可能表明存在滞后现象的可能性，因此海冰损失是不可逆转的。
Winter Arctic sea ice loss has been simulated with varying degrees of abruptness across global climate models (GCMs) run in phase 5 of the Coupled Model Intercomparison Project (CMIP5) under the high-emissions extended RCP8.5 scenario. Previous studies have proposed various mechanisms to explain modeled abrupt winter sea ice loss, such as the existence of a wintertime convective cloud feedback or the role of the freezing point as a natural threshold, but none have sought to explain the variability of the abruptness of winter sea ice loss across GCMs. Here we propose a year-to-year local positive feedback cycle in which warm, open oceans at the start of winter allow for the moistening and warming of the lower atmosphere, which in turn increases the downward clear-sky longwave radiation at the surface and suppresses ocean freezing. This situation leads to delayed and diminished winter sea ice growth and allows for increased shortwave absorption from lowered surface albedo during springtime. Last, the ocean stores this additional heat throughout the summer and autumn seasons, setting up even warmer ocean conditions that lead to further sea ice reduction. We show that the strength of this feedback, as measured by the partial temperature contributions of the different surface heat fluxes, correlates strongly with the abruptness of winter sea ice loss across models. Thus, we suggest that this feedback mechanism may explain intermodel spread in the abruptness of winter sea ice loss. In models in which the feedback mechanism is strong, this may indicate the possibility of hysteresis and thus irreversibility of sea ice loss.