Ocean heat records have been breaking for months. This is the first global evidence of the impacts...
It has triggered the fourth global mass coral bleaching event, according to the US National Oceanic and Atmospheric Administration.
Bleaching happens when coral gets stressed and turns white because the water it lives in is too hot.
The bleached coral can look beautiful in pictures but scientists that dive to examine the reefs say that up close the coral is clearly ill and decaying.
Like many researchers, she was shocked when she saw coral turning white in the first mass bleaching in 1998.
Coral can recover from heat stress but it needs time - ideally several years.
"If given a chance, coral are actually resilient and can recover. But as bleaching becomes more frequent and stronger in intensity, we're really narrowing that window," says Dr Emma Camp at the University of Technology Sydney, Australia.
Research published last week gave some hope that coral that living in cooler, deeper water - at between 30-50m depth - in the Great Barrier Reef can survive for longer than shallow corals as the planet warms.
The research shows that deeper water coral could survive global warming of up to 3C compared to pre-industrial times, says Jennifer McWhorter at NOAA who authored the research with the university of Exeter.
All the coral scientists BBC News spoke to said that we must accept that reefs as we know them will permanently change and small-scale restoration work cannot save coral globally.
Only a rapid and global reduction in greenhouse gas emissions that limits ocean warming will guarantee we have at least some coral left, they say.