Global warming exceeding a modest 2ºC above pre-industrial levels could mean the end of coral reefs as prominent coastal eco-systems, a study suggests.

Warming will have to be kept down to below 1.5ºC to protect at least half of the reefs worldwide, say the researchers, whose study is published in the journal Nature Climate Change.

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 2000 coral reef sites.

Too much heat breaks down the vital symbiotic relationship between coral and the algae that live within them, and on which they rely as an energy source. This causes the coral to turn pale, or "bleach". If the bleaching goes on for too long, the coral dies.

In 1998 an estimated 16% of corals were lost in a single prolonged episode of worldwide warmth.