Could CO2 be a greater threat to marine life than plastic?

Could CO₂ Be a Bigger Threat to Marine Life Than Plastic?

Rising CO₂ isn’t just a climate talking point—it’s a hidden menace beneath the waves that could eclipse plastic pollution in its devastation of marine ecosystems. While plastic debris litters our beaches and headlines, escalating CO₂ concentrations are stealthily cooking the oceans, triggering mass coral bleaching events that obliterate habitats for a quarter of all marine species . As political will to meet global warming targets wanes, this “invisible threat” is fast becoming the greatest peril to ocean life.

CO₂, Ocean Heat, and the Bleaching Crisis

Burning fossil fuels elevates atmospheric CO₂, which 90% of excess heat absorbs into the oceans, raising sea surface temperatures to lethal levels for corals . When waters exceed typical summer highs by just 1 °C for prolonged periods, corals expel their symbiotic algae, turning bone-white in mass bleaching events that can kill up to 39% of corals on affected reefs and, in extreme cases, more than 95% of sensitive species like Acropora .

The current fourth global bleaching event has already exposed 84% of the world’s reefs to bleaching-level heat—far surpassing the 68% in the 2014–2017 event—and continues to accelerate . In some regions, surveys recorded 72% coral mortality on surveyed reef flats, leaving behind lifeless “graveyards of coral” where vibrant ecosystems once thrived .

The Biodiversity at Stake

Though covering under 1% of the ocean floor, coral reefs support roughly 25% of marine species—over one million species, including 4,000 fish species, countless invertebrates, and endangered sea turtles and sharks . Reef structures provide nursery grounds, feeding areas, and spawning sites essential for fisheries that feed and employ millions globally. When reefs bleach and die, entire food webs collapse, leading to sharp declines in fish biomass and echinoderm populations—a direct threat to food security for coastal communities .

Bleaching-induced habitat loss can reduce fish populations by more than 50% within years, as juveniles lose critical shelter and predators find fewer hiding spots . The decline of herbivorous fish like parrotfish further exacerbates reef degradation, allowing algae to overgrow and smother any surviving corals .

Paradoxically, as scientific urgency peaks, political focus on CO₂ reduction is slipping. Recent calls by influential figures to “reset” net-zero policies reveal growing skepticism toward ambitious climate targets . In some regions, climate denialists have pivoted their messaging to energy costs and security, sidelining emissions cuts in favor of short-term economic narratives . This retreat from decisive climate action undermines commitments under the Paris Agreement to limit warming to 1.5 °C—precisely the threshold beyond which coral recovery becomes nearly impossible.