Human-caused climate change, not El Niño, is the driving force behind all global coral bleaching events, new research finds

Climate Central-led paper finds human-caused climate change has been the main driver of coral bleaching risk over the past 40 years.

PRINCETON, N.J., July 23, 2026 /PRNewswire/ -- Nearly every global coral bleaching event over the past 40 years would not have occurred without human-caused climate change, according to new research published in Oceanography.

While El Niño is often mistakenly viewed as the cause of widespread coral bleaching events — in 1998, 2010, 2014-2017, and 2018-2025 — fossil fuel-driven ocean heat is the fundamental force behind bleaching and coral mortality. Scientists used a multi-model extreme event attribution method to assess the influence of climate change on sea surface temperatures. They then applied those results to the bleaching risk model developed by NOAA's Coral Reef Watch and found a clear climate change influence on coral bleaching risk.

During the 2018-2025 event, the analysis indicates there would have been essentially no coral bleaching and certainly not a global-scale event without human-caused climate change. Of the 71 regions where coral bleaching was observed, only one region would have had a moderate risk of bleaching in a world without climate change. Similar results were found for all other global events. For each, climate change was necessary to push temperatures over the bleaching risk threshold.

"Our study shows that without climate change, coral bleaching would be a rare and isolated event, and global mass coral bleaching simply would not occur," said Andrew Pershing, Chief Program Officer at Climate Central and lead author of the study. "Millions of people and entire countries rely on healthy coral reefs for livelihoods and food security. But our emissions of carbon pollution are causing increasingly widespread damage and death to these vital and vibrant ecosystems. Without immediate emissions reduction, coral reefs as we know them will disappear."

Using the same methodology, scientists projected the risk of coral bleaching during the 2026-2027 El Niño event now underway. While natural El Niño-driven warming may lead to low levels of bleaching risk in a few regions, human-caused climate change is likely to drive coral bleaching across the globe, particularly in the southern Caribbean, the Central and South American coasts, and the coasts of eastern Asia.

Discussions of global coral bleaching events are tied more to El Niño than climate-fueled ocean warming. However, researchers found that, under current warming rates, the effect of rising temperatures due to human-caused climate change will outweigh the impact from El Niño in all coral-containing regions by 2028.

This research adds to the evidence that coral reefs worldwide are at increasing risk despite their ability to adapt to warming conditions. Without intervention and a reduction in carbon-polluting emissions, additional warming increases the likelihood that coral reef ecosystems as we know them could disappear for good.

SOURCE Climate Central