Coral reefs worldwide are experiencing unprecedented bleaching events due to rising sea temperatures, with 84% of exposed reefs showing heat stress levels since 2023, according to NOAA. The latest global event began on January 1, 2023, and has been observed across at least 83 countries and territories.
Bleaching occurs when heat disrupts the coral’s metabolism, causing it to turn white as it expels symbiotic algae that provide nutrients and color. Prolonged bleaching can kill corals, but it doesn’t mean they’re dead. Rising sea temperatures made this year’s events more frequent and severe, with regional water temperature changes also contributing to the risk of bleaching.
Since the early 1980s, coral bleaching events have increased in frequency and severity due to fossil fuel burning driving global warming. The last global event occurred between 2014-2017, with 68% of reefs experiencing heat stress. More frequent bleaching leaves little time for corals to recover, resulting in long-term declines.
Mass bleaching often coincides with El Niño episodes, which increased temperatures in 1998, 2016, and last year, the warmest year on record. Oceans absorb rising temperatures but have broken records in 2023-2024, causing acidification that can dissolve corals’ skeletons.
A recent marine heat wave off Florida’s coast caused significant bleaching, prompting NOAA to introduce a new bleaching alert scale with three categories for higher coral mortality rates. Coral bleaching begins at four degree-heating weeks and can lead to ecosystem degradation and flooding hazards.
Coral reefs support 30% of all marine biodiversity and provide essential ecosystem services worth billions to the US economy each year. While corals’ resilience offers some hope, scientists stress that addressing climate change is crucial for their survival.
Source: https://www.washingtonpost.com/climate-environment/2025/04/23/coral-reef-bleaching-record-heat-stress