The Great Barrier Reef is not a single reef but 2,900 individual reefs and 900 islands stretching 1,400 miles along Queensland's coast. The reef system covers 134,000 square miles - larger than Italy. It's built entirely by coral polyps: tiny animals related to jellyfish that secrete calcium carbonate skeletons.

The current reef is about 8,000 years old, built on the foundations of older reefs killed by sea level changes. The polyps build slowly - a few centimeters per year - but over millennia, they created a structure visible from orbit. It's the only living thing that can be seen from space.

The reef supports extraordinary biodiversity: over 1,500 fish species, 400 coral species, 4,000 mollusk species, and 240 bird species. Six of the world's seven sea turtle species breed here. Dugongs graze on seagrass beds. Humpback whales migrate through annually.

The diversity exists because coral reefs are the rainforests of the sea - complex three-dimensional structures that create countless niches for life. Remove the coral, and the entire ecosystem collapses. Fish lose shelter. Predators lose prey. The web unravels.

Coral bleaching occurs when water temperatures rise. The coral expels the symbiotic algae that give it color and provide 90% of its nutrition. The coral turns white - 'bleached.' If temperatures return to normal quickly, the coral can recover. If not, it starves and dies.

Mass bleaching events occurred in 1998, 2002, 2016, 2017, 2020, 2022, and 2024. Each event kills more coral. The 2016-2017 events killed half the coral in the northern third of the reef. The bleaching is caused by climate change - ocean temperatures are rising as the planet warms. There is no solution except reducing greenhouse gas emissions globally.

Australia has invested billions in reef protection: controlling agricultural runoff, limiting fishing, monitoring water quality. Scientists are experimenting with heat-resistant coral strains, coral gardening, and cloud brightening to reduce temperatures.

But the fundamental problem - global ocean warming - is beyond Australia's control. The reef's survival depends on global climate action. UNESCO has repeatedly considered listing the reef as 'in danger.' Australia has resisted, fearing the economic and political implications. The reef contributes $9 billion annually to Australia's economy and supports 77,000 jobs.

Without dramatic reduction in global emissions, the Great Barrier Reef may be largely dead by 2050. Some scientists say it's already too late - the warming already locked in will bleach the remaining coral. Others hold hope that heat-resistant coral species might survive and rebuild.

What's certain is that the reef your grandchildren may visit will not be the reef you visit today. The colors will be muted. The diversity diminished. The largest living structure on Earth is dying in real time, one bleaching event at a time. The coral that took 8,000 years to build may take just decades to destroy.