Extended Data Fig. 2: Spatial extent of observed and simulated MHWs over the satellite data taking period.

a, Histogram of the spatial extent of satellite-observed MHWs above the climatological (1982–2016) 99th percentile for the 1982–1998 (blue) and 1999–2016 (red) period. b, The spatial pattern of the MHW with the largest extent in the satellite data taking period (1982–2016), which occurred on 2 September 2015 in the North Pacific and was associated with the ‘the Blob’²¹. It had a spatial extent of about twice the area of the United States (that is, 1.85 × 10⁷ km²). Shown are SST anomalies above the 1982–2016 climatological 99th percentile on 2 September 2015. The colour bar shows degrees Celsius. c, Comparison between satellite-based observations (black line) and simulations (red histogram) of the spatial extent of MHWs above the climatological 99th percentile over the 1982–2016 period. The number of MHWs (y axis) is normalized with the total number of MHWs. Deeper red colour indicates a greater number of overlapping models.