By Marco Lopez – Climate Spotlight Editor
Unprecedented heat stress has impacted 83.7% of the world’s coral reefs from January 2023, when the 4th global coral bleaching event commenced, to April 20, 2025. At least 83 countries and territories have been documented in this mass coral bleaching event.
The latest data from the US government’s Coral Reef Watch shows this global coral bleaching event is the biggest to date. The 3rd event, which took place from 2014 – 2017, affected 68.2% of the world’s reefs. The second, in 2010, affected 37%, while the first global bleaching event recorded in 1998 affected 21% of global coral reefs.
Never-before-seen heat stress driven by the continued proliferation of fossil fuels is worsening climate change and pushing these rainforests of the sea to their brink. Putting at risk the biodiversity fostered by a healthy reef system that supports a billion human beings and a third of all marine species.
Despite this, as the proverbial underwater wildfires continue to spread, making ashy graveyards of once vibrant, life-filled reefscapes – the political will of world leaders to ramp up the use of renewable energy and eventually phase out of fossil fuels remains lacking, if not nonexistent.
Back-to-back years of heat stress, like we are experiencing with this bleaching event give impacted coral no time to recover and drive up rates of mortality. This is now being seen in reefs across once thought to be resistant to heat stress. Experts believe that the fact that this bleaching event is still ongoing puts the world’s reefs in uncharted waters.
Following the extreme heat in 2023, Coral Reef Watch had to add three new threat levels to its global bleaching alert system.
The ongoing heat stress also puts a pause on coral restoration efforts and drastically limits those people who do pivotal monitoring.
For those who do restoration and monitoring, spending their lives at sea, seeing how corals are currently suffering is nothing short of devastating.
Besides bleaching, other stressors like Stony Coral Tissue Loss, White band, and Black band disease add to coral stress and mortality.
Ecological grief is real – for the people seeing these changes who have been working with coral for years, the urgency to materialize the solutions needed to address the root causes of climate change needs to increase tenfold.
