Most of the world's coral could be wiped out if greenhouse gas emissions are not reined in over the next 10 years, scientists have warned.
Global warming that exceeds a modest 2C above pre-industrial levels could mean the end of coral reefs as prominent coastal ecosystems, a study suggests.
Warming will have to be kept down to below 1.5C to protect at least half of the reefs worldwide, say the researchers.
Dr Malte Meinshausen, one of the scientists from the Potsdam Institute for Climate Research in Germany, said: "The window of opportunity to preserve the majority of coral reefs, part of the world's natural heritage, is small. We close this window if we follow another decade of ballooning global greenhouse gas emissions."
The scientists used a set of 19 global climate simulations to predict the cumulative heat stress on more than 2,000 coral reef sites worldwide.
Too much heat breaks down the vital symbiotic relationship between coral and the algae that live within them, and which they rely on as an energy source. This causes the coral to turn pale, or "bleach". If the bleaching goes on for too long the coral die.
In 1998 an estimated 16% of corals were lost in a single prolonged episode of worldwide warmth.
The new study, published in the journal Nature Climate Change, took into account the effects of greater ocean acidity caused by carbon absorption, which makes corals less able to withstand warm temperatures.
Professor Ove Hoegh-Guldberg, another member of the team from the University of Queensland in Australia, pointed out that corals were not equipped to evolve heat resistance quickly enough.
"They have long lifecycles of five to 100 years and they show low levels of diversity due to the fact that corals can reproduce by cloning themselves," he said. "They are not like fruit flies which can evolve much faster."