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The Impact of Climate Change on the Coral Reefs

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Scientists warn that coral reefs worldwide are experiencing mass bleaching due to climate change, with many reefs not expected to recover from the intense, prolonged heat stress. At least 54 countries and territories have experienced mass bleaching along their reefs since February 2023, according to the US National Oceanic Atmospheric Administration’s (NOAA) Coral Reef Watch. Corals are invertebrates that live in colonies, and their calcium carbonate secretions form a protective scaffolding that serves as a home to many colourful species of single-celled algae. Coral bleaching is triggered by water temperature anomalies that cause corals to expel the colourful algae living in their tissues, which prevents corals from receiving the nutrients they need to survive.

Over the past year, sea surface temperatures have smashed records that have been kept since 1979, as the effects of El Nino are compounded by climate change. Like this year’s bleaching event, the last three (1998, 2010, and 2014-2017) also coincided with an El Nino climate pattern, typically ushering in warmer sea temperatures. The Great Barrier Reef, the most extensive coral reef system in the world and the only one visible from space has been severely impacted, as it has vast swathes of the South Pacific, the Red Sea, and the Gulf. Recurring bleaching events are also upending earlier scientific models that forecast that between 70% and 90% of the world’s coral reefs could be lost when global warming reaches 1.5 degrees Celsius (2.7 F) above pre-industrial temperatures, with most available evidence suggesting that coral-dominated ecosystems will be non-existent at this temperature.

Scientists have warned that many of the world’s reefs may not recover from the intense, prolonged heat stress and that the situation is new for them and science. Even if corals survive immediate heat stress, scientists cannot predict how severely stressed corals will do. This year’s global bleaching event adds further weight to concerns among scientists that corals are in grave danger. Ecologist David Obura, who heads Coastal Oceans Research and Development Indian Ocean East Africa from Mombasa, Kenya, said that a realistic interpretation is that coral reefs have crossed the tipping point and are going into a decline that cannot be stopped unless carbon dioxide emissions that are driving climate change are stopped.

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