Fig. 1: Observed record-breaking North Atlantic Sea Surface Temperature (SST) anomaly in 2023.

a Daily anomalies of SST with respect to the 1991-2020 mean from the OSTIA dataset averaged over the North Atlantic (NATL, 80°W–0°W, 10°N-60°N) region shown in black in the inset map, for 2023 (red), 2022 (blue) and the years of observed record annual SST for the 1990, 2000 and 2010 decades (grey). Dashed horizontal lines stand for yearly average in 2023 and 2022. The yellow shading corresponds to the May–June seasonal window studied in this paper. b Map of standardised SST anomaly for May–June 2023. The yellow contour outlines the region where the anomaly exceeds the 1991–2020 standard deviation, defining the horseshoe-shaped area that encompasses the strongest large-scale warming. c Same as (a) but for the horseshoe domain.