Signal 2025 bleaching event exposed 84.4 percent of reef area

Summary

In 2025 the largest coral bleaching event on record exposed 84.4 percent of the world's reef area to heat stress strong enough to cause bleaching. The report's key take-aways describe this as the most severe mass bleaching tropical reefs have experienced so far. The event is presented as evidence of accelerating warming and more frequent marine heatwaves. The report groups warm-water coral reefs with the Amazon rainforest and boreal forests as biomes that can show tipping behaviour. It considers warm-water reefs in particular likely to be tipping already. This fits the report's broader judgement that the impacts of crossing planetary boundaries are visible now rather than in a distant future.