Jason Momoa isn't just playing a superhero on screen anymore. The actor and United Nations Environment Programme Advocate for Life Below Water is sounding an alarm about a catastrophe unfolding in real time: coral reefs are dying at a scale scientists have never documented before.
On 15 April 2024, the National Oceanic and Atmospheric Administration confirmed the fourth global coral bleaching event. The numbers are staggering. Between 1 January 2023 and 30 September 2025, bleaching-level heat stress affected approximately 84.4% of the world's coral reef area. Mass bleaching was documented in at least 83 countries and territories across the Pacific, Atlantic and Indian oceans. NOAA said the global event likely ended in mid-2025, but the agency also noted something more troubling: identifying when these events begin and end is becoming increasingly difficult because coral reefs are now experiencing heat stress more frequently.
What's at stake
Coral reefs aren't abstract environmental concerns. They feed families. In Hawai'i, Momoa points out, reefs help sustain coastal communities and remain deeply connected to Hawaiian cultural traditions. They protect coastlines from storms and support the marine biodiversity that hundreds of millions of people depend on for food and livelihoods. When reefs disappear, entire ways of life vanish with them.
The science behind bleaching is straightforward but alarming. Corals live in a symbiotic relationship with microscopic algae called zooxanthellae, which provide energy through photosynthesis and give corals their color. When ocean temperatures rise beyond what a coral can tolerate, the coral expels the algae and turns white—bleached. Bleaching doesn't automatically mean death. Some colonies can recover if temperatures return to normal. But prolonged stress causes starvation, disease and death. The damage depends on how long the heat lasts, which coral species we're talking about, and local environmental conditions. Repeated bleaching leaves reefs with insufficient time to recover between heatwaves.
A study published in Coral Reefs in January 2026 examined coral heat stress between 1985 and 2025. Researchers found that an uninterrupted period of global coral heat stress from 2018 to 2025 affected 87% of reef areas worldwide—the highest proportion recorded in the study. Median heat stress accumulation across reef areas was nearly 50% greater than during the previous global bleaching event record. Coral reefs are entering an era of more frequent bleaching, with less time to recover between major disturbances.
The human causes
Climate change is the primary driver, but it's not the only one. Momoa identifies plastic pollution, coastal development, agricultural runoff and overfishing as additional sources of damage. Plastic waste injures coral colonies. Sediment and pollutants from construction and farming reduce water quality. Overfishing disrupts marine food webs and affects species that play important roles in maintaining reef health. These aren't forces of nature—they're choices societies make about how to develop coastlines, manage agriculture and extract resources from the ocean.
The projections are grim. An opinion article published by The Guardian on 17 April 2026 and republished by UNEP said up to 90% of coral reefs could disappear by 2050 under 1.5°C of global warming, while losses could reach 99% at 2°C. The Intergovernmental Panel on Climate Change has warned that reef-building corals face substantial losses even at 1.5°C of global warming above pre-industrial levels.
What's being done
Conservation organisations and scientists are working on coral restoration, reef monitoring and research into heat-tolerant coral species. Projects include coral nurseries, restoration programmes and efforts to identify colonies that may withstand warmer conditions. These efforts matter, but they have limits. Restoration can support damaged reefs in suitable locations, but its success depends on water quality, the level of destruction and future environmental conditions. Protecting healthy reefs remains essential because established ecosystems may be more resilient than severely degraded ones.
Measures such as reducing pollution, protecting coastal habitats and improving fisheries management can help strengthen reef resilience. But here's the crucial constraint: local conservation efforts must be supported by action to reduce global greenhouse gas emissions. No amount of reef restoration can overcome the warming caused by continued fossil fuel burning. The future of coral reefs depends on how effectively governments, organisations and communities address rising temperatures and local environmental pressures simultaneously.
Why This Matters:
Coral reefs support the food security and cultural survival of hundreds of millions of people, particularly in developing nations and island communities with the least responsibility for causing climate change. The fourth global bleaching event represents a failure of international climate action and a stark illustration of how environmental degradation disproportionately harms vulnerable populations. When 84% of the world's coral reefs experience bleaching within a three-year period, and scientists find it increasingly difficult to distinguish between separate bleaching events because they're happening so frequently, we're witnessing the collapse of ecosystems faster than our institutions can respond. The combination of climate change, pollution, overfishing and coastal development shows how environmental destruction isn't inevitable—it's the result of policy choices about energy, agriculture, fishing and development. Reversing this trajectory requires both immediate local action to reduce other stressors and binding global commitments to emissions reductions that have so far proven elusive.