2025 Volume 21 Pages 117-123
In 2017/18 winter, the Siberian High intensified significantly, leading to a severe cold winter in central Eurasia. Here, we apply the event attribution methods using two types of historical large-ensemble simulations from an atmospheric general circulation model to quantify the influence of human activities on this event. The 2017/18 winter was dominated by a circulation regime known as the Warm-Arctic Cold-Eurasia (WACE) pattern, and both observation and model showed high WACE indices. However, the models exhibited a bias characterized by weak magnitudes of the cold Eurasian anomalies associated with the WACE, attributed to an underrepresentation of externally driven components. Anthropogenic climate change has increased the probability of the positive WACE regime year by year, significantly enhancing its occurrence in the 2017/18 winter. However, influences of this modulation of WACE occurrence did not significantly alter the probability of cold events in central Eurasia due to the model bias characterized by the muted cold lobe associated with the WACE. While a simple bias correction resolved this issue, it was demonstrated that the presence or absence of such corrections led to vastly different attribution results. Elucidating the mechanisms behind the WACE and accurately representing them in models is essential for more reliable attribution.
