Reefs in areas currently considered colder havens will be overwhelmed at a 1.5°C warming and only 0.2% of reefs will escape at least one bleaching episode every decade, according to the research, The Guardian reports.

Scientists from the University of Leeds, Texas Tech University and James Cook University used the latest climate model projections to confirm that a 1.5°C global warming "will be catastrophic for coral reefs".

About 84% of the world's corals exist in areas that are expected to turn white less than once a decade and are considered "thermal refugia", the study says. But the analysis suggests that at a global warming of 1.5C, only 0.2% of the area covered by reefs is in water cold enough to avoid bleaching at least once every five years - a frequency considered too short to allow corals to recover.

The only area that might escape, the study says, would be a region in the eastern Indian Ocean, in an area of naturally rising colder water. Even areas with strong currents that can protect corals from the heat, such as those in Panama, Florida and Indonesia's Lesser Sunda Islands, would be overwhelmed by the heat.

Corals bleach when ocean temperatures are too high for too long. The algae that provide corals with much of their food and colour separate from corals during heat stress. Severe bleaching can kill corals, but they can recover from milder outbreaks if there are a few years without another heat wave. The world's oceans are warming mainly because of the burning of fossil fuels.

Professor Peter Mumby, a reef expert at the University of Queensland who studies the effects of climate change on corals, agreed that at 1.5°C, corals around the world would be under greater stress than they are now. "But I disagree that this research provides evidence that corals can no longer be sustained under 1.5°C warming," he said.

Mumby said the heat stress levels used in the study to identify severe bleaching were arguably too low, and the method is unlikely to capture local conditions that could protect some reefs. Even reefs that are affected by bleaching every five years could include areas of coral that would survive, according to Mumby.