Coral in some parts of the world will be wiped out within 20 years, according to new research by scientists in the UK.
By Richard Black
BBC science correspondent
Writing in the journal Nature, they say that coral in the Indian Ocean and south-east Asia is especially vulnerable to rising sea temperatures.
Could all this be gone in 20 years?
In 1998 a particularly strong El Nino phenomenon warmed the waters of the Indian Ocean and south-east Asia by several degrees Celsius.
That killed around 90% of the coral in the region.
Though some is slowly growing back, computer models of global warming predict that similarly high temperatures will occur regularly in the future.
If it happens frequently enough, the coral will be killed off completely.
Charles Sheppard from Warwick University has been calculating when the date of this extinction may arrive.
Warm water belt
"There's a belt of the Indian Ocean between the Equator to about 15 or so degrees to the south where this extinction date is going to happen by about 2020, maybe 2025, which is bad news.
"That also includes the area of the Indian Ocean which contains a lot of the poorest countries," he said.
Although Dr Sheppard hasn't done the calculations, he thinks the same will hold true for south-east Asia, where reefs already face a number of other threats, including pollution and brutal fishing methods.
"You can only give probabilities of each year being hot, you cannot say definitely.
"So I calculated how long it will be until you can expect one year in every five to be hot enough to kill off the coral, and I believe that is ecologically sound because it takes coral about five years to mature enough that it can reproduce," he told the BBC.
According to some estimates, coral reefs are the main source of protein for around ten million people worldwide.
They also attract wealthy western tourists and provide a natural breakwater against the worst ravages of ocean storms.
Unfortunately very little is being done to protect them.
If the realisation that some reefs may die permanently within two decades does not act as a spur to action, it is difficult to see what will.