World’s Largest Coral Bleaching Event Unfolds Amid Climate Crisis

By William J. Furney

A global coral bleaching event, the largest ever recorded, has been unfolding since the beginning of 2023, driven by unprecedented ocean temperatures.

According to data from the US National Oceanic and Atmospheric Administration (NOAA), 77% of the world’s coral reefs have been exposed to severe bleaching, surpassing the previous record of 65.7% within half the time. This widespread bleaching, occurring across the Atlantic, Pacific and Indian Oceans, threatens not only marine ecosystems but also the livelihoods of communities reliant on reefs for food and economic activity.

Coral bleaching occurs when ocean temperatures rise beyond the tolerance of corals, causing them to expel the algae living within their tissues. These algae provide corals with food and give them their vibrant colours. Without the algae, corals turn white, losing their ability to sustain themselves. As a result, they become vulnerable to disease and can die off if the heat stress continues for too long.

The current bleaching event is the fourth major one since 1998 and has been exacerbated by marine heatwaves. The NOAA’s Derek Manzello told the AFP news agency that “roughly 77 percent of the world’s reef area has experienced bleaching-level heat stress” between January 2023 and October 2024. It has surpassed the previous global bleaching event, which lasted from 2014 to 2017, in less than half the time.

The impacts of such mass bleaching are devastating, say researchers. Corals play a crucial role in maintaining the health of the oceans by providing shelter and food for marine species. They also protect coastlines from storms and support industries like fishing and tourism, which are vital for millions of people worldwide. Without healthy reefs, marine ecosystems face collapse, threatening biodiversity and human livelihoods alike.

NOAA’s satellite data reveals that the extent and intensity of the current coral bleaching are directly linked to rising ocean temperatures. This year’s global heatwaves have affected vast areas, including Florida and Australia’s Great Barrier Reef, which has experienced five mass bleaching events in just eight years.

Climate change has accelerated ocean warming, with NOAA and other climate monitors reporting that the pace of ocean heating has almost doubled since 2005. In 2023, 20% of the world’s oceans experienced severe to extreme marine heatwaves, further compounding the stress on coral reefs.

While coral bleaching doesn’t always result in immediate death, recovery becomes increasingly difficult as these events become more frequent and prolonged, and efforts are underway to protect and restore coral reefs. Governments and environmental organisations are focusing on reducing other stressors, such as overfishing and pollution, that can further weaken coral ecosystems. Marine protected areas offer some respite, although enforcement can be weak, especially in developing regions.

In addition to localised efforts, international cooperation will be critical in addressing the broader climate crisis. A UN biodiversity summit in Colombia next week will hold an emergency session dedicated to the mass coral bleaching event. Experts will present the latest scientific data and discuss strategies to prevent the functional extinction of coral reefs.

The ongoing global coral bleaching event is a stark reminder of the urgent need to address climate change. The survival of coral reefs, which support one-quarter of all marine species, hangs in the balance. As global temperatures continue to rise, the likelihood of future bleaching events will only increase, pushing coral ecosystems to the brink of collapse.

Immediate and aggressive action to curb greenhouse gas emissions is essential to protect the remaining coral reefs. Experts agree that limiting global warming to 1.5°C, as outlined in the Paris Agreement, is crucial. Beyond this threshold, the chances of saving coral reefs diminish drastically.

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