The Great Barrier Reef may not outlast this generation, if conditions don’t improve.

A UN climate report released on Monday identified 127 major consequences of rising global temperatures, some of them already happening, some of them irreversible. One particularly grim one, mentioned alongside wildfires and sea-level rise, is the fate of Australia’s Great Barrier Reef, one of the most biodiverse ecosystems on Earth.

The reef is already in crisis and has been for years, damaged by the coral trade, by overfishing, by channels blasted through it with explosives, by rising temperatures and acid levels in the ocean. One of the most obvious injuries it suffers regularly are mass bleaching events, when warm temperatures cause coral to expel all of their symbiotic algae colonies living in their tissues. The process turns formerly colorful coral white, causing it to reflect light instead of absorb it, a cooling mechanism. While bleaching itself doesn’t kill the coral, it leaves it weak, starving, and subject to many things that will kill it. Expanses of reef that bleach usually lose between half and seventy-percent of their live coral in the months after. Coral can also bleach when pollutant levels rise, or in unseasonable bouts of cold water, though we don’t yet know why.

In 2016, at the time the warmest year on record, a catastrophic bleaching event affected nearly the entire Great Barrier Reef, over 90%. Since then, the events have been non-stop – some part of the reef is always undergoing bleaching. The northern and middle parts of the 1400-mile-long reef system are highly degraded and dozens of coral species found only there are believed to have gone extinct.

Divers who see bleaching go through waters familiar to them compare it to a wildfire. In only weeks, it turns vibrant, living expanses of reef ecosystem into gray moonscapes with water so full of dead coral and algae that it’s slimy and milky white.

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