Researchers have added three new levels to a coral bleaching warning system in response to the unprecedented marine heatwaves experienced in 2023. The National Oceanic and Atmospheric Administration’s Coral Reef Watch program revamped its bleaching alert system to provide additional detail for coral reef managers to prepare and take action during extreme heat stress. Coral bleaching occurs when corals expel the algae within their tissues due to stress caused by changes in temperature, light, or nutrients. Increased ocean temperature, caused by climate change, is the leading cause of coral bleaching. The revamped system now ranges from level one to level five, indicating the risk of reef-wide bleaching to near-complete mortality.