Since 1982, just after mass bleachings were seen for the first time, the data shows that the average proportion of the Great Barrier Reef exposed to temperatures where bleaching or death is likely has increased from about 11% a year to about 27% a year.

Eakin says looking at that data revealed a clear trend that hadn’t been quantified before. “In seeing that what it immediately showed was that there was a real background pattern of increasing levels of thermal stress.”

Combined with other stressors hitting the reef, this is having a devastating impact. Over that period, half the coral cover on the Great Barrier Reef has been lost – and that’s before the mass bleaching this year is taken into account.

That data has limitations – it’s not direct bleaching, but stress inferred from temperature readings. And it lumps extreme levels of stress – like what is being seen around Lizard Island now – with anything that is expected to cause mortality.

Despite that, it reveals the way global warming is leading to more regular bleaching and mortality.

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The Great Barrier Reef: A Catastrophe Laid Bare

By Michael Slezak

7 June 2016

https://www.theguardian.com/environment/2016/jun/07/the-great-barrier-reef-a-catastrophe-laid-bare