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How dead is the Great Barrier Reef?

A video explainer on coral bleaching, the No. 1 threat to coral reefs around the world.

Australia's Great Barrier Reef is the largest coral reef system in the world and the only living structure visible from space. Although ecosystem managers in Australia have worked hard to preserve the reefs, the past couple of decades have brought a new threat that can't be solved by any one country alone: human-induced global warming.

Rising ocean temperatures have caused mass bleaching in coral reefs around the world, from the Caribbean to the South Pacific. The Great Barrier Reef suffered back-to-back mass bleaching in the summers of 2016 and 2017, highlighting the fact that the increasing frequency of bleaching will leave little time for the reefs to recover. Scientists now consider bleaching to be the biggest threat that coral reefs face — and they face many, including overfishing, pollution, storm damage, and invasive species.

To learn how coral reefs work, and why rising temperatures are such a threat to this ecosystem, check out the video above, and subscribe to our YouTube channel for more explainer videos.