北极地区人为强迫的放大：一个向量自回归分析
Arctic Amplification of Anthropogenic Forcing: A Vector Autoregressive Analysis
摘要：
2020年9月15日，北极海冰范围（SIE）在历史上排名倒数第二，并继续下降。对反馈回路如何放大外部CO2强迫效应的理解仍然有限。我们提出了VARCTIC，这是一个向量自回归（VAR），旨在捕捉和外推北极反馈回路。VAR是动态联立方程组，通常用于预测和理解多个宏观经济时间序列的相互作用。VARCTIC是成熟的气候模型和纯粹的统计方法之间的一种折衷，这种方法通常对潜在的机制几乎没有解释。我们完全无条件地预测，到2060年，SIE将在9月达到0。脉冲响应函数表明，人为CO2排放冲击有一个不寻常的持久影响SIE -财产共享没有其他冲击。我们发现，反照率和厚度为基础的反馈是主要的放大渠道，通过它CO2异常影响SIE在短期/中期运行。此外，有条件的预测分析表明，SIE的未来路径关键取决于CO2排放的演变，结果从恢复SIE到2050年达到0。最后，反照率和厚度的反馈显示，在加速预测SIE走向0的速度发挥了重要作用。
英文摘要：
On September 15th 2020, Arctic sea ice extent (SIE) ranked second-to-lowest in history and keeps trending downward. The understanding of how feedback loops amplify the effects of external CO2 forcing is still limited. We propose the VARCTIC, which is a Vector Autoregression (VAR) designed to capture and extrapolate Arctic feedback loops. VARs are dynamic simultaneous systems of equations, routinely estimated to predict and understand the interactions of multiple macroeconomic time series. The VARCTIC is a parsimonious compromise between full-blown climate models and purely statistical approaches that usually offer little explanation of the underlying mechanism. Our completely unconditional forecast has SIE hitting 0 in September by the 2060's. Impulse response functions reveal that anthropogenic CO2 emission shocks have an unusually durable effect on SIE -- a property shared by no other shock. We find Albedo- and Thickness-based feedbacks to be the main amplification channels through which CO2 anomalies impact SIE in the short/medium run. Further, conditional forecast analyses reveal that the future path of SIE crucially depends on the evolution of CO2 emissions, with outcomes ranging from recovering SIE to it reaching 0 in the 2050's. Finally, Albedo and Thickness feedbacks are shown to play an important role in accelerating the speed at which predicted SIE is heading towards 0.
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