“It’s hard to imagine what that would look like” said Prof Peter Mumby, one of the study’s authors.

Even under the most ambitious scenario where heating is kept to 1.5C, coral bleaching strong enough to kill corals would hit somewhere on the reef more than three times a decade, the study predicts.

Allowing global heating to go beyond 2C would bring unprecedented levels of heat stress.

“It’s hard to imagine what that would look like” said Prof Peter Mumby, one of the study’s authors.

Using the latest climate models, the scientists added extra information about the depth, tides and winds around reefs to give a more detailed projection of how much bleaching could occur over different areas.

Lead author of the study, Jen McWhorter, said the modelling suggested warming above 2C would be “very, very bad” for corals along the reef.

But she said keeping temperatures to 1.5C – the most ambitious target in the Paris climate change agreement – meant corals were exposed to far less heat stress.

“The stress we see above 2C under these higher [greenhouse gas] emissions scenarios is three to four times greater than present day conditions,” said McWhorter, who has a combined role at the University of Exeter and the University of Queensland.

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