What the study found
The study found an uninterrupted period of global coral heat stress from 2018 to 2025, affecting an unprecedented 87% of reef areas globally. It also found that the 4th global coral bleaching event, called GCBE4, is the most extensive and intensive on record.
Why the authors say this matters
The authors conclude that GCBE4 marks a period of heat stress that is unprecedented by every investigated metric. They also say that many reef areas are now in an era of near-annual bleaching, meaning bleaching-level heat stress has persisted for almost the entire last decade.
What the researchers tested
The researchers defined an objective, quantifiable index to compare satellite-derived coral heat stress accumulation globally from 1985 to 2025. They then examined how those heat-stress periods related to confirmed global-scale coral bleaching events.
What worked and what didn't
The analysis showed record-setting average intensity, with the median global heat stress accumulation on reef areas nearly 50% greater than the previous GCBE record. The study also reports that recent baseline global surface ocean temperatures from 2019 to 2023 were comparable to extreme anomalous conditions seen about 25 years earlier, and that a strong El Niño event in 2023 added to the warming and culminated in GCBE4. Qualitative bleaching observations were reported from 84 countries, and the extent and magnitude of heat stress suggest bleaching may have affected 98 of 102 countries with coral reefs.
What to keep in mind
The abstract describes an analysis based on satellite-derived heat stress and qualitative bleaching observations, so the country-level bleaching estimate is presented as a suggestion rather than a direct confirmed count. The abstract does not describe additional limitations beyond the scope of the metrics and observations reported.
Key points
- Global coral heat stress was continuous from 2018 to 2025.
- An estimated 87% of reef areas globally were affected.
- GCBE4 is described as the most extensive and intensive global coral bleaching event on record.
- Median global heat stress accumulation was nearly 50% higher than the previous record.
- Bleaching observations were reported from 84 countries, and heat stress suggests possible impact in 98 of 102 coral reef countries.
Disclosure
- Research title:
- Global coral heat stress reached record levels from 2018 to 2025
- Authors:
- Blake L. Spady, William Skirving, Jacqueline L. De La Cour, Erick Geiger, Gang Liu, Ove Hoegh-Guldberg, Andrew Norrie, Scott F. Heron, Morgan Pomeroy, Graham Kolodziej, Kristen T. Brown, Derek P. Manzello
- Institutions:
- Earth System Science Interdisciplinary Center, Global Science & Technology (United States), Global Science & Technology (United States), Global Science & Technology (United States), Global Science & Technology (United States), Global Science & Technology (United States), James Cook University, James Cook University, NOAA National Environmental Satellite Data and Information Service, NOAA National Environmental Satellite Data and Information Service, NOAA National Environmental Satellite Data and Information Service, NOAA National Environmental Satellite Data and Information Service, NOAA National Environmental Satellite Data and Information Service, NOAA National Environmental Satellite Data and Information Service, NOAA National Environmental Satellite Data and Information Service, NOAA National Environmental Satellite Data and Information Service, Reef Ecologic, Reef Ecologic, The University of Queensland, University of Maryland, College Park, University of Reading
- Publication date:
- 2026-01-29
- OpenAlex record:
- View
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