Understanding Coral Bleaching: FAQs Answered

Coral Reefs at a Tipping Point: FAQs

What is coral bleaching and why does it happen?

Coral bleaching occurs when corals expel the symbiotic algae (zooxanthellae) living in their tissues due to stress caused by high sea temperatures. This loss of algae turns corals white and leaves them vulnerable to disease and starvation. Since these algae provide most of the coral’s nutrients through photosynthesis, prolonged bleaching often results in coral death and large-scale reef decline.

What is the significance of the 1.5°C temperature threshold?

Scientists have identified 1.5°C above pre-industrial levels as the critical limit for warm-water coral ecosystems. Beyond this point, corals face severe, potentially irreversible changes to their environment. In 2024, global average temperatures exceeded 1.5°C for the first time, signaling an unprecedented crisis for coral reefs and marine biodiversity.

Why is this considered a “tipping point”?

A tipping point is a critical threshold beyond which a system undergoes irreversible and self-reinforcing change. For coral reefs, surpassing this threshold could trigger cascading global effects—such as the decline of the Amazon rainforest, accelerated polar ice melt, and the collapse of major ocean circulation systems—all of which may occur at warming levels below 2°C.

What are the economic and ecological consequences of coral reef collapse?

Warm-water coral reefs sustain nearly one-third of all known marine species and provide food security, livelihoods, and coastal protection for almost one billion people globally. The ecosystem services they offer are valued at up to $9.9 trillion annually. Their collapse would not only devastate biodiversity but also pose a significant “human health and security hazard,” for which most governments remain unprepared.

What solutions are proposed to mitigate the risk?

The report emphasizes the urgent need to curtail global greenhouse gas emissions to keep warming below 2°C. Key measures include the rapid expansion of renewable energy, accelerated transition to cleaner technologies, and strong global commitments from world leaders at COP30 to minimize the duration of elevated global temperatures. Immediate and coordinated action is essential to preserve what remains of the world’s coral ecosystems.

What does the latest research reveal about the current state of coral reefs?

According to the Global Tipping Points Report 2025—a study compiled by 160 scientists and coordinated by the University of Exeter and WWF—warm-water coral reefs have become the first major Earth system to cross their tipping point. Researchers from James Cook University, Australia, report that there are now “almost no unbleached reefs left anywhere in the world,” underscoring the urgent need for global restoration and mitigation efforts.