Warming Trends and Bleaching Stress of the World’s Coral Reefs 1985–2012

TLDR

Coral reefs worldwide are experiencing the longest bleaching event on record, and limited data exist on how past thermal conditions have affected reef composition and stress responses. Such analyses can help identify reefs more resilient to thermal stress. Using satellite temperature data from 1985–2012, the study quantified spatial variations in warming trends, thermal stress events, and temperature variability at ~4 km reef scale, producing thermal‑history data products that enable studies of bleaching resistance and community composition. Across more than 60,000 reef pixels, 97 % exhibited positive SST trends, 60 % of which were significant, with annual trends surpassing summertime trends, a prolonged summer‑like temperature period shortening winter reprieves, and bleaching‑level thermal stress frequency tripling from 1985–91 to 2006–12, a rise projected to continue.

Abstract

Abstract Coral reefs across the world’s oceans are in the midst of the longest bleaching event on record (from 2014 to at least 2016). As many of the world’s reefs are remote, there is limited information on how past thermal conditions have influenced reef composition and current stress responses. Using satellite temperature data for 1985–2012, the analysis we present is the first to quantify, for global reef locations, spatial variations in warming trends, thermal stress events and temperature variability at reef-scale (~4 km). Among over 60,000 reef pixels globally, 97% show positive SST trends during the study period with 60% warming significantly. Annual trends exceeded summertime trends at most locations. This indicates that the period of summer-like temperatures has become longer through the record, with a corresponding shortening of the ‘winter’ reprieve from warm temperatures. The frequency of bleaching-level thermal stress increased three-fold between 1985–91 and 2006–12 – a trend climate model projections suggest will continue. The thermal history data products developed enable needed studies relating thermal history to bleaching resistance and community composition. Such analyses can help identify reefs more resilient to thermal stress.