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 coral bleaching in coral reefs around the world, in every tropical ocean from the Caribbean to the South Pacific. This is now considered to be the biggest threat that coral reefs face, and they face many, including overfishing, pollution, storm damage, and invasive species.