No one would challenge the majesty of Australia's Great Barrier Reef.
Nearly 1,500 miles long, the reef is alight with a kaleidoscope of vivid colours. It's home to roughly 9,000 species of fish, molluscs, whales and other creatures. In 1981, the reef was designated a UNESCO World Heritage Site, a status that helps it draw 2 million visitors a year.
It's also dying. At our own hands.
Two major bleaching events have wracked the Great Barrier Reef over the last two years, leaving chunks of it dead. Bleachings happen when the coral expels tiny algae, called zooxanthellae, that live inside it and provide its food and create its rainbow hues. Without zooxanthellae, the reef's tissue turns transparent and the coral starves.