Study: climate change, not El Nino, caused all major coral bleaching events

Human-caused climate change — not El Niño — has been the primary force behind every global coral bleaching event over the past four decades, according to new research published Wednesday in the journal Oceanography.morningstar+1

The study, led by Climate Central, found that none of the major bleaching episodes since 1985 would have reached global scale without the ocean warming driven by fossil fuel emissions. El Niño, long viewed as the catalyst for mass coral die-offs, acts merely as a trigger atop a baseline of human-caused heat that has already pushed reefs to their limits.globalissues+1

Every Global Event Required Human Warming

The researchers analyzed bleaching events in 1998, 2010, 2014–2017, and the ongoing event that began in 2023. For each, climate change was necessary to push ocean temperatures beyond bleaching-risk thresholds. During the 2018–2025 event, the analysis found there would have been "essentially no coral bleaching and certainly not a global-scale event" without human-caused warming. Of the 71 regions where bleaching was observed in that period, only one would have faced even moderate bleaching risk in a world without climate change.morningstar

Andrew Pershing, who leads Climate Central's climate science work and served as lead author, has said the research demonstrates that without climate change, coral bleaching would be rare and isolated.climatecentral+1

A Grim Projection

The study projects that by 2028, human-caused warming will outweigh El Niño's influence in every coral reef region worldwide. The finding underscores the accelerating nature of the threat: reefs are no longer merely vulnerable during El Niño years but face chronic heat stress regardless of natural climate cycles.globalissues

The research arrives amid the fourth global coral bleaching event on record. Since January 2023, bleaching-level heat stress has affected roughly 84 percent of the world's coral reef area, with mass bleaching documented in at least 83 countries and territories, according to NOAA's Coral Reef Watch.coralreefwatch.noaa

Reefs at a Crossroads

The study adds to growing evidence that coral reef ecosystems face an existential crisis without immediate emissions reductions. Scientists have estimated that 30 to 50 percent of coral reefs have already been lost in recent decades, and the current prolonged bleaching event has raised concerns about whether many reefs can recover before the next wave of heat arrives.theconversation

"This research adds to the evidence that coral reefs worldwide are at increasing risk despite their ability to adapt to warming conditions," the researchers noted.morningstar