A multi-decadal baseline of marine temperature extremes across Brazil’s coastal foundation habitats

Abstract Global marine habitats are increasingly threatened by the intensification of climate extremes, such as marine heatwaves (MHWs) and marine cold spells (MCSs). Brazil harbors diverse and endemic marine communities, yet the historical exposure of its coastal habitats to extreme events remains poorly quantified at local scales. Here we assess 40 years of MHWs and MCSs across eight coastal foundation habitats in Brazil using a validated, high-resolution composite sea surface temperature dataset covering over 100,000 sites. Events were characterized by their frequency, duration, and intensity, and classified into Moderate, Strong, Severe, and Extreme categories. We show a pronounced intensification of MHWs, with event frequency and duration increasing across most habitats and Strong events rising by nearly 190% over the past decade. More than half of habitat areas exhibit positive trends in both MHW frequency and duration, with the strongest increases observed in coral reefs (+ 1.5 events per decade; +3.5 days per decade) and seagrass meadows (+ 2.0 events per decade; +5.1 days per decade). In contrast, MCSs declined overall to roughly one-third of previous levels, yet record-intensity (− 4.5 °C) and exceptionally long-lasting (up to 160 days) cold events continue to punctuate the recent climate record in southern coastal habitats. Together, these results reveal strong spatial heterogeneity in exposure to climate extremes and establish a robust, site-specific baseline for assessing coastal ecosystem vulnerability under ongoing climate change.