Split westerly winds over Europe – A breakthrough by an international project led by Department of Geosciences

Europe, even located at the mid-high latitude at 40-70oN, the autumn and winter are mild and comfortable. Such pleasant weather is regulated by the warm and humid westerly winds from the North Atlantic Ocean. During the 15th to 19th century, Europe experienced the coldest winters over the last ten thousand years, known as the “Little Ice Age” (LIA). The LIA was suggested to be caused by volcanic eruptions and low solar activity. However, the detailed climate pattern in Europe remains unclear.
Dr. Hsun-Ming Hu, the first author, and Prof. Chuan-Chou Shen, the leader of this international project, published their latest prominent study(1) of the split westerly winds over Europe during the early LIA in the prestigious journal “Nature Communications” on August 20th. The finding overturns the past understanding of the southward westerly drift during this interval.
In 2018, Dr. Hu collected an 8-cm-long stalagmite in Bàsura cave, northern Italy. By conducting high-precision radiometric U-Th dating techniques and trace element analyses in the HISPEC, Department of Geosciences, NTU, the drifting histories of the westerly winds in Europe-Mediterranean realm were revealed. Comparison of Bàsura records with previous published precipitation data shows that, during the early LIA, the westerly winds not only drifted southerly, but also split into two branches away from mainland Europe. The absence of moisturizing with warm and humid currents in turn resulted in dry and cold winter in Europe. They conclude that the double westerly winds were triggered by frequent high-pressure anomalies over northern Europe.
Model simulations suggest that the frequent high-pressure anomalies over Europe could be induced by both concurrent sea-ice melting at the North Atlantic and low solar activity during the early LIA. Under the ongoing global warming, the North Atlantic sea-ice could keep melting in the coming decades. The scenario revealed in this study could happen again. As a consequence, the ecosystem and Europeans could face severe impacts from droughts. Dr. Hu emphasized that the drift of the westerlies did affect the ancient civilization, such as the collapse of the western Roman Empire(2).

(1) Hu, H.-M. et al. (2022) Split westerlies over Europe in the early Little Ice Age. Nature Communications 13, 4898. https://www.nature.com/articles/s41467-022-32654-w

(2) Hu, H.-M. et al. (2022). Stalagmite-Inferred Climate in the Western Mediterranean during the Roman Warm Period. Climate, 10, 93. https://www.mdpi.com/2225-1154/10/7/93

Dr. Hsun-Ming Hu working in Bàsura cave, northern Italy, in 2018.

A group photograph of the international team, led by Dr. Chuan-Chou Shen of the Department of Geosciences, in front of Bàsura cave, northern Italy.

A stalagmite in Bàsura cave, northern Italy.