84% of Reefs Hit: The Fourth Global Bleaching Event Ends
The worst coral bleaching event on record touched 84% of the world's reefs — and it puts the small, avoidable harm from sunscreen chemicals in sharp context.
By the fourth global coral bleaching event, bleaching-level heat stress affected 84% of the world's coral reef area across 82 countries and territories (Jan 2023-March 2025) — up from 21% in 1998, 37% in 2010 and 68% in 2014-2017 — and NOAA determined the event likely ended in mid-2025.
Coral reef scientists stress that record ocean heat is the dominant driver of this unprecedented bleaching, while noting that reducing additional, avoidable stressors matters more than ever for reefs already pushed to the brink.
Questions we get a lot
How much of the world's reefs were affected by the fourth bleaching event?
Bleaching-level heat stress affected 84% of the world's coral reef area across 82 countries and territories between January 2023 and March 2025. That is well above prior global events, which affected 21% in 1998, 37% in 2010 and 68% in 2014-2017. NOAA later determined the event likely ended in mid-2025.
Does sunscreen really harm coral reefs?
Record ocean heat is the dominant driver of mass bleaching, not sunscreen. However, some sunscreen chemicals are an additional stressor on reefs that are already under extreme pressure. Choosing reef-conscious products is one small, avoidable harm to reduce while broader climate action addresses the heat.
r/sustainability: 'If ocean heat is the real reef killer, does switching to reef-safe sunscreen even make a difference?'