The marine heatwave west of Ireland in June 2023

Abstract

The summer of 2023 had been notable for a number of climate extremes: sea ice in the Antarctic dropped to its lowest for the time of year since satellite records began in the 1970s (NASA Earth Observatory, 2023), terrestrial heatwaves engulfed southern Europe and southern United States/Mexico that would have been ‘virtually impossible’ without climate change (WorldWeatherAttribution, 2023), and sea-surface temperatures (SSTs) in the North Atlantic reached their highest since satellite records began in 1982 (NOAA, 2023). In concert with these terrestrial heatwaves and high Atlantic SSTs, a severe marine heatwave(MHW) developed in the eastern North Atlantic, west of Ireland (Figure 1a). Except for a narrow band close to the coast from Greenland to Canada, SSTs everywhere in the North Atlantic were above the 41-yearaverage (1982–2023), with many regions experiencing temperatures 2 degC higher than average. In the study region westof Ireland (highlighted in Figure 1b), the SST reached an impressive 4 degC above average.