Early-onset trend in European summer caused by Greenland topographic effect

Global heating, which is considered irreversible at least for the near future, causes various climate crises directly affecting human life. Accordingly, European countries have been afflicted by frequent heatwaves in summer. Convolutional neural network deep learning models have revealed the lengthening of the European summer over the past 42 years. Here we show that the early onset of summer is responsible for this climatic trend. In late May, an anti-cyclonic circulation anomaly strengthens over the United Kingdom, Ireland, and the adjoining Atlantic Ocean, causing significant temperature increases across Western Europe, Iceland, and around the Barents Sea. The intensification of the mid-latitude westerly wind impinging on Greenland seems to be responsible for strengthening the anomalous circulation change via topographically forced stationary Rossby wave responses. As the westerly wind intensification is ensued by further global heating, summer will begin earlier, and thus more frequent European heatwaves are expected to occur.